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一、mybatis-config.xml转为Document对象
配置文件的入口：
private static final String NAME_SPACE = "UserMapper.";
private static SqlSessionFactory ssf;
private static Reader reader;
static {
try {
// 作用：相当读取配置文件，并将其转换成流的形式返回。
reader = Resources.getResourceAsReader("mybatis-config.xml");
ssf = new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
}
}
Resources.getResourceAsReader(“mybatis-config.xml”)的代码实现如下：
public static Reader getResourceAsReader(String resource) throws IOException {
Reader reader;
if (charset == null) {
reader = new InputStreamReader(getResourceAsStream(resource));
} else {
reader = new InputStreamReader(getResourceAsStream(resource), charset);
}
return reader;
}
SqlSessionFactory是通过SqlSessionFactoryBuilder工厂类的build方法创建的， 不是通过构造方法直接new出来的。
此外，我们还可以知道，SqlSessionFactory提供了字节流和字符流以及直接的org.apache.ibatis.session.Configuration配置类的三种方式来读取配置文件信息。但是无论是字符流还是字节流，然后将Configuration设置到SqlSessionFactory（默认的实现类是org.apache.ibatis.session.defaults.DefaultSqlSessionFactory）中的configuraion字段并且返回。所以其本身也是很简单的，解析xml配置文件的操作都委托给了XMLConfigBuilder类。
public class SqlSessionFactoryBuilder {
// ···省略其他无关代码
public SqlSessionFactory build(Reader reader) {
return build(reader, null, null);
}
// 最终调用的是此方法
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
// ···省略其他无关代码
}
XMLConfigBuilder类的主要代码如下：
XMLConfigBuilder以及解析Mapper.xml文件的XMLMapperBuilder都继承自BaseBuilder。他们对xml文件的加载和解析都交给了XPathParser，从而最终使用JDK自带的xml解析器而非dom4j、jdom第三方jar包，底层使用xPath进行节点解析（不了解xPath的可以去学习下）。new XPathParser(reader, true, props, new XMLMapperEntityResolver()) 四个参数的含义分别是：配置文件流、是否进行DTD校验、属性配置、xml实体节点解析器。EntityResolver比较好理解，跟Spring的XML标签解析器一样，有默认的解析器，也有自定义的比如tx，dubbo等，主要使用了策略模式，在这里mybatis硬编码为了XMLMapperEntityResolver
public class XMLConfigBuilder extends BaseBuilder {
private boolean parsed;
private final XPathParser parser;
private String environment;
private final ReflectorFactory localReflectorFactory = new DefaultReflectorFactory();
//1.先走这里
public XMLConfigBuilder(Reader reader) {
this(reader, null, null);
}
// 2.进入这里，创建XPathParser器
public XMLConfigBuilder(Reader reader, String environment, Properties props) {
this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
}
public XMLConfigBuilder(InputStream inputStream) {
this(inputStream, null, null);
}
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
}
// 3.最终都会调用此方法，再次之前会进入XPathParser类中进行一系列初始化操作，见下。
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
// 省略其他无关代码
}
XPathParser类代码如下：
补充一下：EntityResolver的作用：EntityResolver的实现类XMLEntityResolver类中引用了本地的DTD文件，和本类在同一个package下，其中的ibatis-3-config.dtd应该主要是用于兼容用途。
其次就是XPathParser做了以下几件事：1.将是否验证dtd,节点解析器进行设置，并且初始化xPath,便于xml文件解析和加载。2.可知，commonConstructor并没有做什么。回过头到createDocument上，其使用了org.xml.sax.InputSource作为参数。代码实现如下：
public class XPathParser {
private final Document document;
private boolean validation;
private EntityResolver entityResolver;
private Properties variables;
private XPath xpath;
public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {
// 1.将是否验证dtd,节点解析器进行设置，并且初始化xPath,便于xml文件解析和加载
commonConstructor(validation, variables, entityResolver);
// 2.可知，commonConstructor并没有做什么。回过头到createDocument上，其使用了org.xml.sax.InputSource作为参数，createDocument的关键代码如下：
this.document = createDocument(new InputSource(inputStream));
}
// 创建document文档
private Document createDocument(InputSource inputSource) {
// important: this must only be called AFTER common constructor
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(validation);
// 设置有本工厂创建的解析器文件是否支持xml命名空间
factory.setNamespaceAware(false);
factory.setIgnoringComments(true);
// 是否忽略元素配置中的空格
factory.setIgnoringElementContentWhitespace(false);
// 设置是否将CDATA节点转换为Text节点
factory.setCoalescing(false);
// 设置是否展开实体节点，关系到sql片段的相关配置
factory.setExpandEntityReferences(true);
DocumentBuilder builder = factory.newDocumentBuilder();
// 设置解析mybatis-config.xml文档节点的解析器，也就是上面的XmlMapperEntityResolver
builder.setEntityResolver(entityResolver);
builder.setErrorHandler(new ErrorHandler() {
@Override
public void error(SAXParseException exception) throws SAXException {
throw exception;
}
@Override
public void fatalError(SAXParseException exception) throws SAXException {
throw exception;
}
@Override
public void warning(SAXParseException exception) throws SAXException {
}
});
return builder.parse(inputSource);
} catch (Exception e) {
throw new BuilderException("Error creating document instance. Cause: " + e, e);
}
}
//主要进行一些配置
private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) {
this.validation = validation;
this.entityResolver = entityResolver;
this.variables = variables;
XPathFactory factory = XPathFactory.newInstance();
this.xpath = factory.newXPath();
}
// ···省略其他无关代码···
}
主要是根据mybatis自身需要创建一个=文档解析器，调用parse方法（inputstream int）.将解析后的xml以document对象的形式返回。如下：
public class XMLConfigBuilder extends BaseBuilder {
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
}
可以看出：主要调用了父类BaseBuilder的构造方法（作用：进行类型别名处理器注册、类型处理器注册）
public abstract class BaseBuilder {
protected final Configuration configuration;
protected final TypeAliasRegistry typeAliasRegistry;
protected final TypeHandlerRegistry typeHandlerRegistry;
public BaseBuilder(Configuration configuration) {
// 出入的新new出来的Configuration对象，Configuration类的初始化的做了一些事情，后面讲具体是什么事。
this.configuration = configuration;
// 别名处理器
this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
// 类型处理器
this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
}
}
之后，设置environment及props等核心配置信息，（Configuration类是MyBatis的核心配置类，十分重要）。XmlConfigBuilder创建完毕之后，代码会回到SqlSessionFactoryBuilder类build(Reader reader, String environment, Properties properties)方法中，然后调用parser.parse()方法。至此，第一阶段：加载xml配置文件并转为Document对象完毕，而所有的配置过程都在parse()这个方法中（也是对Configuration类的配置）。
二、Document对象转为Configuration对象
之前的步骤将mybatis-config.xml转为了Document对象，下一步就是将Document转换为MyBatis中的Configuration类对象。其主要步骤在XMLConfigBuilder类中的parseConfiguration(XNode root)方法进行。如下：
public class SqlSessionFactoryBuilder {
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
}
XMLConfigBuilder类：
通过parseConfiguration(parser.evalNode("/configuration"))得知，xml文件中的configuration中的内容已经全部加载到XNode中了，后续的相关配置数据的获取都是通过这个XNode来获取的。
public class XMLConfigBuilder extends BaseBuilder {
private boolean parsed;
private final XPathParser parser;
private String environment;
private final ReflectorFactory localReflectorFactory = new DefaultReflectorFactory();
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
// 解析的主要流程都在这：后面会详细介绍。
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
}
2.1 MyBatis dtd和Configuration类
先来看看MyBatis dtd的约束文件：
位置在：
<?xml version="1.0" encoding="UTF-8" ?>
<!--
Copyright 2009-2016 the original author or authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<!ELEMENT configuration (properties?, settings?, typeAliases?, typeHandlers?, objectFactory?, objectWrapperFactory?, reflectorFactory?, plugins?, environments?, databaseIdProvider?, mappers?)>
<!ELEMENT databaseIdProvider (property*)>
<!ATTLIST databaseIdProvider
type CDATA #REQUIRED
>
<!ELEMENT properties (property*)>
<!ATTLIST properties
resource CDATA #IMPLIED
url CDATA #IMPLIED
>
<!ELEMENT property EMPTY>
<!ATTLIST property
name CDATA #REQUIRED
value CDATA #REQUIRED
>
<!ELEMENT settings (setting+)>
<!ELEMENT setting EMPTY>
<!ATTLIST setting
name CDATA #REQUIRED
value CDATA #REQUIRED
>
<!ELEMENT typeAliases (typeAlias*,package*)>
<!ELEMENT typeAlias EMPTY>
<!ATTLIST typeAlias
type CDATA #REQUIRED
alias CDATA #IMPLIED
>
<!ELEMENT typeHandlers (typeHandler*,package*)>
<!ELEMENT typeHandler EMPTY>
<!ATTLIST typeHandler
javaType CDATA #IMPLIED
jdbcType CDATA #IMPLIED
handler CDATA #REQUIRED
>
<!ELEMENT objectFactory (property*)>
<!ATTLIST objectFactory
type CDATA #REQUIRED
>
<!ELEMENT objectWrapperFactory EMPTY>
<!ATTLIST objectWrapperFactory
type CDATA #REQUIRED
>
<!ELEMENT reflectorFactory EMPTY>
<!ATTLIST reflectorFactory
type CDATA #REQUIRED
>
<!ELEMENT plugins (plugin+)>
<!ELEMENT plugin (property*)>
<!ATTLIST plugin
interceptor CDATA #REQUIRED
>
<!ELEMENT environments (environment+)>
<!ATTLIST environments
default CDATA #REQUIRED
>
<!ELEMENT environment (transactionManager,dataSource)>
<!ATTLIST environment
id CDATA #REQUIRED
>
<!ELEMENT transactionManager (property*)>
<!ATTLIST transactionManager
type CDATA #REQUIRED
>
<!ELEMENT dataSource (property*)>
<!ATTLIST dataSource
type CDATA #REQUIRED
>
<!ELEMENT mappers (mapper*,package*)>
<!ELEMENT mapper EMPTY>
<!ATTLIST mapper
resource CDATA #IMPLIED
url CDATA #IMPLIED
class CDATA #IMPLIED
>
<!ELEMENT package EMPTY>
<!ATTLIST package
name CDATA #REQUIRED
>
从dtd文件可以看出：mybatis-config.xml文件中最多有11个配置项，分别是properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,reflectorFactory?,plugins?,environments?,databaseIdProvider?,mapper?,但是所有的配置都是可选的，这意味着mybatis-config配置文件本身可以什么都不包含。因为所有的配置最后保存到org.apache.ibatis.session.Configuration中，所以在详细查看每块配置的解析前，我们来看下Configuration的内部完整结构：
public class Configuration {
protected Environment environment;
// 允许在嵌套语句中使用分页（RowBounds),如果允许使用则设置成false。默认为false.
protected boolean safeRowBoundsEnabled;
// 允许在嵌套语句中使用分页。如果允许设置为false.
protected boolean safeResultHandlerEnabled = true;
// 是否开启自动驼峰命名规则（camel case)映射。如user_name ---> userName，默认false
protected boolean mapUnderscoreToCamelCase;
// 当开启时，任何方法的调用都会加载该对象的所有属性。否则，每个属性则按需加载。默认是false.
protected boolean aggressiveLazyLoading;
// 是否允许单一语句返回多结果集（需要兼容驱动）
protected boolean multipleResultSetsEnabled = true;
// 允许JDBC自动生成主键，需要驱动兼容。这就是insert时获取mysql自增或oralce sequence的开关。开发中，一般希望插入后获取主键，所以设置成true.
protected boolean useGeneratedKeys；
// 使用列标签代替列名，开发中一半进行配置。
protected boolean useColumnLabel = true;
// 是否开启缓存
protected boolean cacheEnabled = true;
// 指定当结果集中值为 null 的时候是否调用映射对象的 setter（map 对象时为 put）方法，这对于有 Map.keySet() 依赖或 null 值初始化的时候是有用的
protected boolean callSettersOnNulls;
// 允许使用方法签名中的名称作为语句参数名称。 为了使用该特性，你的工程必须采用Java 8编译，并且加上-parameters选项。（从3.4.1开始）
protected boolean useActualParamName = true;
// 当返回行的所有列都是空时，MyBatis默认返回null。 当开启这个设置时，MyBatis会返回一个空实例。 请注意，它也适用于嵌套的结果集 (i.e. collectioin and association)。（从3.4.2开始） 注：这里应该拆分为两个参数比较合适, 一个用于结果集，一个用于单记录。通常来说，我们会希望结果集不是null，单记录仍然是null
protected boolean returnInstanceForEmptyRow;
// 指定 MyBatis 增加到日志名称的前缀。
protected String logPrefix;
// 指定 MyBatis 所用日志的具体实现，未指定时将自动查找。一般建议指定为slf4j或log4j
protected Class <? extends Log> logImpl;
// 指定VFS的实现, VFS是mybatis提供的用于访问AS内资源的一个简便接口
protected Class <? extends VFS> vfsImpl;
// MyBatis 利用本地缓存机制（Local Cache）防止循环引用（circular references）和加速重复嵌套查询。 默认值为 SESSION，这种情况下会缓存一个会话中执行的所有查询。 若设置值为 STATEMENT，本地会话仅用在语句执行上，对相同 SqlSession 的不同调用将不会共享数据
protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
// 当没有为参数提供特定的 JDBC 类型时，为空值指定 JDBC 类型。 某些驱动需要指定列的 JDBC 类型，多数情况直接用一般类型即可，比如 NULL、VARCHAR 或 OTHER
protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
// 指定对象的哪个方法触发一次延迟加载
protected Set<String> lazyLoadTriggerMethods = new HashSet<String>(Arrays.asList(new String[] { "equals", "clone", "hashCode", "toString" }));
// 设置超时时间，它决定驱动等待数据库响应的秒数。默认不超时
protected Integer defaultStatementTimeout;
// 为驱动的结果集设置默认获取数量
protected Integer defaultFetchSize;
// SIMPLE 就是普通的执行器；REUSE 执行器会重用预处理语句（prepared statements）； BATCH 执行器将重用语句并执行批量更新
protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
// 指定 MyBatis 应如何自动映射列到字段或属性。 NONE 表示取消自动映射；PARTIAL 只会自动映射没有定义嵌套结果集映射的结果集。 FULL 会自动映射任意复杂的结果集（无论是否嵌套）
protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;
// 指定发现自动映射目标未知列（或者未知属性类型）的行为。这个值应该设置为WARNING比较合适
protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
// settings下的properties属性
protected Properties variables = new Properties();
// 默认的反射器工厂,用于操作属性、构造器方便
protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
// 对象工厂, 所有的类resultMap类都需要依赖于对象工厂来实例化
protected ObjectFactory objectFactory = new DefaultObjectFactory();
// 对象包装器工厂,主要用来在创建非原生对象,比如增加了某些监控或者特殊属性的代理类
protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
// 延迟加载的全局开关。当开启时，所有关联对象都会延迟加载。特定关联关系中可通过设置fetchType属性来覆盖该项的开关状态
protected boolean lazyLoadingEnabled = false;
// 指定 Mybatis 创建具有延迟加载能力的对象所用到的代理工具。MyBatis 3.3+使用JAVASSIST
protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
// MyBatis 可以根据不同的数据库厂商执行不同的语句，这种多厂商的支持是基于映射语句中的 databaseId 属性。
protected String databaseId;
/**
* Configuration factory class.
* Used to create Configuration for loading deserialized unread properties.
*
* @see <a href='https://code.google.com/p/mybatis/issues/detail?id=300'>Issue 300 (google code)</a>
*/
protected Class<?> configurationFactory;
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
// mybatis插件列表
protected final InterceptorChain interceptorChain = new InterceptorChain();
// 类型注册器, 用于在执行sql语句的出入参映射以及mybatis-config文件里的各种配置比如<transactionManager type="JDBC"/><dataSource type="POOLED">时使用简写, 后面会详细解释
protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection");
protected final Map<String, Cache> caches = new StrictMap<Cache>("Caches collection");
protected final Map<String, ResultMap> resultMaps = new StrictMap<ResultMap>("Result Maps collection");
protected final Map<String, ParameterMap> parameterMaps = new StrictMap<ParameterMap>("Parameter Maps collection");
protected final Map<String, KeyGenerator> keyGenerators = new StrictMap<KeyGenerator>("Key Generators collection");
protected final Set<String> loadedResources = new HashSet<String>();
protected final Map<String, XNode> sqlFragments = new StrictMap<XNode>("XML fragments parsed from previous mappers");
protected final Collection<XMLStatementBuilder> incompleteStatements = new LinkedList<XMLStatementBuilder>();
protected final Collection<CacheRefResolver> incompleteCacheRefs = new LinkedList<CacheRefResolver>();
protected final Collection<ResultMapResolver> incompleteResultMaps = new LinkedList<ResultMapResolver>();
protected final Collection<MethodResolver> incompleteMethods = new LinkedList<MethodResolver>();
/*
* A map holds cache-ref relationship. The key is the namespace that
* references a cache bound to another namespace and the value is the
* namespace which the actual cache is bound to.
*/
protected final Map<String, String> cacheRefMap = new HashMap<String, String>();
public Configuration(Environment environment) {
this();
this.environment = environment;
}
public Configuration() {
// 内置别名注册
typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
typeAliasRegistry.registerAlias("LRU", LruCache.class);
typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
languageRegistry.register(RawLanguageDriver.class);
}
// 省略部分无关代码
/** @deprecated Use {@link #getDefaultScriptingLanguageInstance()} */
@Deprecated
public LanguageDriver getDefaultScriptingLanuageInstance() {
return getDefaultScriptingLanguageInstance();
}
public MetaObject newMetaObject(Object object) {
return MetaObject.forObject(object, objectFactory, objectWrapperFactory, reflectorFactory);
}
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
return parameterHandler;
}
public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,
ResultHandler resultHandler, BoundSql boundSql) {
ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
return resultSetHandler;
}
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
public Executor newExecutor(Transaction transaction) {
return newExecutor(transaction, defaultExecutorType);
}
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor;
if (ExecutorType.BATCH == executorType) {
executor = new BatchExecutor(this, transaction);
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
executor = new SimpleExecutor(this, transaction);
}
if (cacheEnabled) {
executor = new CachingExecutor(executor);
}
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
public void addKeyGenerator(String id, KeyGenerator keyGenerator) {
keyGenerators.put(id, keyGenerator);
}
public Collection<String> getKeyGeneratorNames() {
return keyGenerators.keySet();
}
public Collection<KeyGenerator> getKeyGenerators() {
return keyGenerators.values();
}
public KeyGenerator getKeyGenerator(String id) {
return keyGenerators.get(id);
}
public boolean hasKeyGenerator(String id) {
return keyGenerators.containsKey(id);
}
public void addCache(Cache cache) {
caches.put(cache.getId(), cache);
}
public Collection<String> getCacheNames() {
return caches.keySet();
}
public Collection<Cache> getCaches() {
return caches.values();
}
public Cache getCache(String id) {
return caches.get(id);
}
public boolean hasCache(String id) {
return caches.containsKey(id);
}
public void addResultMap(ResultMap rm) {
resultMaps.put(rm.getId(), rm);
checkLocallyForDiscriminatedNestedResultMaps(rm);
checkGloballyForDiscriminatedNestedResultMaps(rm);
}
public Collection<String> getResultMapNames() {
return resultMaps.keySet();
}
public Collection<ResultMap> getResultMaps() {
return resultMaps.values();
}
public ResultMap getResultMap(String id) {
return resultMaps.get(id);
}
public boolean hasResultMap(String id) {
return resultMaps.containsKey(id);
}
public void addParameterMap(ParameterMap pm) {
parameterMaps.put(pm.getId(), pm);
}
public Collection<String> getParameterMapNames() {
return parameterMaps.keySet();
}
public Collection<ParameterMap> getParameterMaps() {
return parameterMaps.values();
}
public ParameterMap getParameterMap(String id) {
return parameterMaps.get(id);
}
public boolean hasParameterMap(String id) {
return parameterMaps.containsKey(id);
}
public void addMappedStatement(MappedStatement ms) {
mappedStatements.put(ms.getId(), ms);
}
public Collection<String> getMappedStatementNames() {
buildAllStatements();
return mappedStatements.keySet();
}
public Collection<MappedStatement> getMappedStatements() {
buildAllStatements();
return mappedStatements.values();
}
public Collection<XMLStatementBuilder> getIncompleteStatements() {
return incompleteStatements;
}
public void addIncompleteStatement(XMLStatementBuilder incompleteStatement) {
incompleteStatements.add(incompleteStatement);
}
public Collection<CacheRefResolver> getIncompleteCacheRefs() {
return incompleteCacheRefs;
}
public void addIncompleteCacheRef(CacheRefResolver incompleteCacheRef) {
incompleteCacheRefs.add(incompleteCacheRef);
}
public Collection<ResultMapResolver> getIncompleteResultMaps() {
return incompleteResultMaps;
}
public void addIncompleteResultMap(ResultMapResolver resultMapResolver) {
incompleteResultMaps.add(resultMapResolver);
}
public void addIncompleteMethod(MethodResolver builder) {
incompleteMethods.add(builder);
}
public Collection<MethodResolver> getIncompleteMethods() {
return incompleteMethods;
}
public MappedStatement getMappedStatement(String id) {
return this.getMappedStatement(id, true);
}
public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
if (validateIncompleteStatements) {
buildAllStatements();
}
return mappedStatements.get(id);
}
public Map<String, XNode> getSqlFragments() {
return sqlFragments;
}
public void addInterceptor(Interceptor interceptor) {
interceptorChain.addInterceptor(interceptor);
}
public void addMappers(String packageName, Class<?> superType) {
mapperRegistry.addMappers(packageName, superType);
}
public void addMappers(String packageName) {
mapperRegistry.addMappers(packageName);
}
public <T> void addMapper(Class<T> type) {
mapperRegistry.addMapper(type);
}
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
public boolean hasMapper(Class<?> type) {
return mapperRegistry.hasMapper(type);
}
public boolean hasStatement(String statementName) {
return hasStatement(statementName, true);
}
public boolean hasStatement(String statementName, boolean validateIncompleteStatements) {
if (validateIncompleteStatements) {
buildAllStatements();
}
return mappedStatements.containsKey(statementName);
}
public void addCacheRef(String namespace, String referencedNamespace) {
cacheRefMap.put(namespace, referencedNamespace);
}
/*
* Parses all the unprocessed statement nodes in the cache. It is recommended
* to call this method once all the mappers are added as it provides fail-fast
* statement validation.
*/
protected void buildAllStatements() {
if (!incompleteResultMaps.isEmpty()) {
synchronized (incompleteResultMaps) {
// This always throws a BuilderException.
incompleteResultMaps.iterator().next().resolve();
}
}
if (!incompleteCacheRefs.isEmpty()) {
synchronized (incompleteCacheRefs) {
// This always throws a BuilderException.
incompleteCacheRefs.iterator().next().resolveCacheRef();
}
}
if (!incompleteStatements.isEmpty()) {
synchronized (incompleteStatements) {
// This always throws a BuilderException.
incompleteStatements.iterator().next().parseStatementNode();
}
}
if (!incompleteMethods.isEmpty()) {
synchronized (incompleteMethods) {
// This always throws a BuilderException.
incompleteMethods.iterator().next().resolve();
}
}
}
/*
* Extracts namespace from fully qualified statement id.
*
* @param statementId
* @return namespace or null when id does not contain period.
*/
protected String extractNamespace(String statementId) {
int lastPeriod = statementId.lastIndexOf('.');
return lastPeriod > 0 ? statementId.substring(0, lastPeriod) : null;
}
// Slow but a one time cost. A better solution is welcome.
protected void checkGloballyForDiscriminatedNestedResultMaps(ResultMap rm) {
if (rm.hasNestedResultMaps()) {
for (Map.Entry<String, ResultMap> entry : resultMaps.entrySet()) {
Object value = entry.getValue();
if (value instanceof ResultMap) {
ResultMap entryResultMap = (ResultMap) value;
if (!entryResultMap.hasNestedResultMaps() && entryResultMap.getDiscriminator() != null) {
Collection<String> discriminatedResultMapNames = entryResultMap.getDiscriminator().getDiscriminatorMap().values();
if (discriminatedResultMapNames.contains(rm.getId())) {
entryResultMap.forceNestedResultMaps();
}
}
}
}
}
}
// Slow but a one time cost. A better solution is welcome.
protected void checkLocallyForDiscriminatedNestedResultMaps(ResultMap rm) {
if (!rm.hasNestedResultMaps() && rm.getDiscriminator() != null) {
for (Map.Entry<String, String> entry : rm.getDiscriminator().getDiscriminatorMap().entrySet()) {
String discriminatedResultMapName = entry.getValue();
if (hasResultMap(discriminatedResultMapName)) {
ResultMap discriminatedResultMap = resultMaps.get(discriminatedResultMapName);
if (discriminatedResultMap.hasNestedResultMaps()) {
rm.forceNestedResultMaps();
break;
}
}
}
}
}
protected static class StrictMap<V> extends HashMap<String, V> {
private static final long serialVersionUID = -4950446264854982944L;
private final String name;
public StrictMap(String name, int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor);
this.name = name;
}
public StrictMap(String name, int initialCapacity) {
super(initialCapacity);
this.name = name;
}
public StrictMap(String name) {
super();
this.name = name;
}
public StrictMap(String name, Map<String, ? extends V> m) {
super(m);
this.name = name;
}
@SuppressWarnings("unchecked")
public V put(String key, V value) {
if (containsKey(key)) {
throw new IllegalArgumentException(name + " already contains value for " + key);
}
if (key.contains(".")) {
final String shortKey = getShortName(key);
if (super.get(shortKey) == null) {
super.put(shortKey, value);
} else {
super.put(shortKey, (V) new Ambiguity(shortKey));
}
}
return super.put(key, value);
}
public V get(Object key) {
V value = super.get(key);
if (value == null) {
throw new IllegalArgumentException(name + " does not contain value for " + key);
}
if (value instanceof Ambiguity) {
throw new IllegalArgumentException(((Ambiguity) value).getSubject() + " is ambiguous in " + name
+ " (try using the full name including the namespace, or rename one of the entries)");
}
return value;
}
private String getShortName(String key) {
final String[] keyParts = key.split("\\.");
return keyParts[keyParts.length - 1];
}
protected static class Ambiguity {
final private String subject;
public Ambiguity(String subject) {
this.subject = subject;
}
public String getSubject() {
return subject;
}
}
}
}
mybatis中所有环境配置、resultMap集合、sql语句集合、插件列表、缓存、加载的xml列表、类型别名、类型处理器等全部都维护在Configuration中。Configuration中包含了一个内部静态类StrictMap，它继承于HashMap，对HashMap的装饰在于增加了put时防重复的处理，get时取不到值时候的异常处理，这样核心应用层就不需要额外关心各种对象异常处理,简化应用层逻辑。
从设计上来说，我们可以说Configuration并不是一个thin类(也就是仅包含了属性以及getter/setter)，而是一个rich类，它对部分逻辑进行了封装便于用户直接使用,而不是让用户各自散落处理，比如addResultMap方法和getMappedStatement方法等等
mybatis每个配置属性含义可参考:官方：配置文件
可以看出官方文档的配置项其实Configuration类的字段。
从Configuration构造器和protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();可以看出，所有我们在mybatis-config和mapper文件中使用的类似int/string/JDBC/POOLED等字面常量最终解析为具体的java类型都是在typeAliasRegistry构造器和Configuration构造器执行期间初始化的。
接下里我们将分块进行分析：
2.2 propertiesElement解析
XMLConfigBuilder类中的解析代码：
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
mybatis-config.xml文件中的配置：
<properties resource="org/mybatis/internal/example/config.properties">
<property name="username" value="dev_user"/>
<property name="password" value="F2Fa3!33TYyg"/>
</properties>
代码如下
private void propertiesElement(XNode context) throws Exception {
if (context != null) {
// 加载properties结点为default
Properties defaults = context.getChildrenAsProperties();
String resource = context.getStringAttribute("resource");
String url = context.getStringAttribute("url");
// resource和url只能二选一
if (resource != null && url != null) {
throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");
}
// 合并properties
if (resource != null) {
defaults.putAll(Resources.getResourceAsProperties(resource));
} else if (url != null) {
defaults.putAll(Resources.getUrlAsProperties(url));
}
Properties vars = configuration.getVariables();
if (vars != null) {
defaults.putAll(vars);
}
// 设置到parser和configuration中去
parser.setVariables(defaults);
configuration.setVariables(defaults);
}
}
解析代码如下：
思路：先解析mybatis-config.xml配置文件中的properties资源并解析成Properties对象，然后再从resouce或url中加载配置资源也解析为Properties类对象，最后将两者的内容合并到defaults中。最后设置到XPathParser类和Configuration类的variables字段中，这样就可以在整个配置文件使用这些东西。
2.3 settingsAsProperties设置
mybatis-config.xml文件中的配置：
<settings>
<setting name="cacheEnabled" value="true" />
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="useGeneratedKeys" value="true"/>
</settings>
代码如下：
private Properties settingsAsProperties(XNode context) {
if (context == null) {
return new Properties();
}
// 1.加载setting标签下的对象为Properties对象
Properties props = context.getChildrenAsProperties();
// Check that all settings are known to the configuration class
MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
for (Object key : props.keySet()) {
if (!metaConfig.hasSetter(String.valueOf(key))) {
throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive).");
}
}
return props;
}
settingsElement(settings)实现：
private void settingsElement(Properties props) throws Exception {
configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), false));
configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
configuration.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null));
configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
@SuppressWarnings("unchecked")
Class<? extends TypeHandler> typeHandler = (Class<? extends TypeHandler>)resolveClass(props.getProperty("defaultEnumTypeHandler"));
configuration.setDefaultEnumTypeHandler(typeHandler);
configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));
configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));
configuration.setLogPrefix(props.getProperty("logPrefix"));
@SuppressWarnings("unchecked")
Class<? extends Log> logImpl = (Class<? extends Log>)resolveClass(props.getProperty("logImpl"));
configuration.setLogImpl(logImpl);
configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
}
思路：
一、先把settings结点解析成Properties对象；然后加载MetaClass类对props中的key的合法性进行校验（可以不能乱写，必须是框架支持的定义过的）；最后如果全部校验通过，就会返回合法的settings对象，否则有一个不通过就会抛出异常。
二、其后在调用settingsElement(settings)方法，把解析到的配置文件信息注入Configuration类的属性中去。
关于MetaClass作用补充：
public static MetaClass forClass(Class<?> type, ReflectorFactory reflectorFactory) {
// new 出来
return new MetaClass(type, reflectorFactory);
}
MetaClass 类构造器：
public class MetaClass {
private final ReflectorFactory reflectorFactory;
private final Reflector reflector;
// 调用的构造器
private MetaClass(Class<?> type, ReflectorFactory reflectorFactory) {
this.reflectorFactory = reflectorFactory;
this.reflector = reflectorFactory.findForClass(type);
}
}
默认的DefaultReflectorFactory类：
public class DefaultReflectorFactory implements ReflectorFactory {
@Override
public Reflector findForClass(Class<?> type) {
if (classCacheEnabled) {
// synchronized (type) removed see issue #461
Reflector cached = reflectorMap.get(type);
if (cached == null) {
cached = new Reflector(type);
reflectorMap.put(type, cached);
}
return cached;
} else {
// 最终会new Reflector(class)，实际注入的参数是Configuration类type
return new Reflector(type);
}
}
}
Reflector类及构造器：
作用：把configuration类相关的类元信息进行解析装载到reflector中去。
public class Reflector {
private final Class<?> type;
private final String[] readablePropertyNames;
private final String[] writeablePropertyNames;
private final Map<String, Invoker> setMethods = new HashMap<String, Invoker>();
private final Map<String, Invoker> getMethods = new HashMap<String, Invoker>();
private final Map<String, Class<?>> setTypes = new HashMap<String, Class<?>>();
private final Map<String, Class<?>> getTypes = new HashMap<String, Class<?>>();
private Constructor<?> defaultConstructor;
private Map<String, String> caseInsensitivePropertyMap = new HashMap<String, String>();
public Reflector(Class<?> clazz) {
type = clazz;
addDefaultConstructor(clazz);
addGetMethods(clazz);
addSetMethods(clazz);
addFields(clazz);
readablePropertyNames = getMethods.keySet().toArray(new String[getMethods.keySet().size()]);
writeablePropertyNames = setMethods.keySet().toArray(new String[setMethods.keySet().size()]);
for (String propName : readablePropertyNames) {
caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
}
for (String propName : writeablePropertyNames) {
caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
}
}
到此可以看出：最后通过 !metaConfig.hasSetter(String.valueOf(key)代码看出：通过判断configuration类中是否有settings文件中的配置key的setter方法，才算校验通过。
2.4 加载自定义VFS：loadCustomVfs(settings)
思路：
VFS主要用来加载容器内的各种资源，比如jar或者class文件。mybatis提供了2个实现 JBoss6VFS 和 DefaultVFS，并提供了用户扩展点，用于自定义VFS实现，加载顺序是自定义VFS实现 > 默认VFS实现 取第一个加载成功的，默认情况下会先加载JBoss6VFS，如果classpath下找不到jboss的vfs实现才会加载默认VFS实现，启动打印的日志如下：
org.apache.ibatis.io.VFS.getClass(VFS.java:111) Class not found: org.jboss.vfs.VFS
org.apache.ibatis.io.JBoss6VFS.setInvalid(JBoss6VFS.java:142) JBoss 6 VFS API is not available in this environment.
org.apache.ibatis.io.VFS.getClass(VFS.java:111) Class not found: org.jboss.vfs.VirtualFile
org.apache.ibatis.io.VFS$VFSHolder.createVFS(VFS.java:63) VFS implementation org.apache.ibatis.io.JBoss6VFS is not valid in this environment.
org.apache.ibatis.io.VFS$VFSHolder.createVFS(VFS.java:77) Using VFS adapter org.apache.ibatis.io.DefaultVFS
jboss vfs的maven仓库坐标为：
<dependency>
<groupId>org.jboss</groupId>
<artifactId>jboss-vfs</artifactId>
<version>3.2.12.Final</version>
</dependency>
找到jboss vfs实现后，输出的日志如下：
org.apache.ibatis.io.VFS$VFSHolder.createVFS(VFS.java:77) Using VFS adapter org.apache.ibatis.io.JBoss6VFS
具体代码实现如下：
private void loadCustomVfs(Properties props) throws ClassNotFoundException {
String value = props.getProperty("vfsImpl");
if (value != null) {
String[] clazzes = value.split(",");
for (String clazz : clazzes) {
if (!clazz.isEmpty()) {
@SuppressWarnings("unchecked")
Class<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz);
configuration.setVfsImpl(vfsImpl);
}
}
}
}
2.5 类型别名解析：typeAliasesElement(root.evalNode(“typeAliases”))
mybatis-config.xml中的如下配置：
<typeAliases>
<typeAlias type="com.gyoomi.entity.User" alias="User"/>
<package name="com.gyoomi"/>
</typeAliases>
代码如下：
private void typeAliasesElement(XNode parent) {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 1-1.package标签配置方式
if ("package".equals(child.getName())) {
String typeAliasPackage = child.getStringAttribute("name");
// 1-2.调用TypeAliasRegistry类的方法进行类的别名注册
configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
} else {
// 2-1typeAlias标签配置形式
String alias = child.getStringAttribute("alias");
String type = child.getStringAttribute("type");
try {
Class<?> clazz = Resources.classForName(type);
if (alias == null) {
// 2-2.如果没有配置别名，默认取类名作为别名
typeAliasRegistry.registerAlias(clazz);
} else {
// 2-3 如果配置了别名和对应的class,直接注册别名即可
typeAliasRegistry.registerAlias(alias, clazz);
}
} catch (ClassNotFoundException e) {
throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
}
}
}
}
}
public class TypeAliasRegistry {
public void registerAliases(String packageName){
// 1-3.调用本类的其他方法
registerAliases(packageName, Object.class);
}
// 1-4.扫描包下的class文件，将符合条件的类进行别名注册，否则不予注册
public void registerAliases(String packageName, Class<?> superType){
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();
for(Class<?> type : typeSet){
// Ignore inner classes and interfaces (including package-info.java)
// Skip also inner classes. See issue #6
if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {
registerAlias(type);
}
}
}
// 1-5. 别名注册
public void registerAlias(Class<?> type) {
String alias = type.getSimpleName();
Alias aliasAnnotation = type.getAnnotation(Alias.class);
if (aliasAnnotation != null) {
alias = aliasAnnotation.value();
}
// --->真正的方法
registerAlias(alias, type);
}
// 1-6.真正的别名注册（也就是往map中添加一个元素）
public void registerAlias(String alias, Class<?> value) {
if (alias == null) {
throw new TypeException("The parameter alias cannot be null");
}
// issue #748
String key = alias.toLowerCase(Locale.ENGLISH);
if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) {
throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + TYPE_ALIASES.get(key).getName() + "'.");
}
TYPE_ALIASES.put(key, value);
}
}
思路：
我们知道typeAliases标签下有两种标签，所以其在解析的时候也是分为两种情况的：package和typeAlias。
第一种如果是包的形式的话：下方标注的 “1-？”是执行的程序。
首先会把配置的包路径名作为参数，调用TypeAliasRegistry类的registerAliases（）方法。
其次在registerAliases(String packageName, Class superType)方法中会根据packageName名称拿到其下的.class文件，并加载到matches集合中去。
再次，遍历mathes中类元素结合，这些类不能是匿名类、接口、内部类才会进行注册；符合条件后调用registerAlias(type)方法，注册别名（本质就是Configuration中的TYPE_ALIASES字段就是一个HashMap添加元素）。
第二种如果是typeAlias的形式的话：下方标注的 “2-？”是执行的程序。
首先取到alias和type。
其次根据是否配置别名（没有配置，默认取小写类名），然后调用registerAlias（）方法进行级完成注册。
补充：
除了上述的这个地方之外，还有两处也进行了系统默认的类名注册。
- Configuration类的构造器中：
public Configuration() {
typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
typeAliasRegistry.registerAlias("LRU", LruCache.class);
typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
languageRegistry.register(RawLanguageDriver.class);
}
- TypeAliasRegistry类的构造器中：
public TypeAliasRegistry() {
registerAlias("string", String.class);
registerAlias("byte", Byte.class);
registerAlias("long", Long.class);
registerAlias("short", Short.class);
registerAlias("int", Integer.class);
registerAlias("integer", Integer.class);
registerAlias("double", Double.class);
registerAlias("float", Float.class);
registerAlias("boolean", Boolean.class);
registerAlias("byte[]", Byte[].class);
registerAlias("long[]", Long[].class);
registerAlias("short[]", Short[].class);
registerAlias("int[]", Integer[].class);
registerAlias("integer[]", Integer[].class);
registerAlias("double[]", Double[].class);
registerAlias("float[]", Float[].class);
registerAlias("boolean[]", Boolean[].class);
registerAlias("_byte", byte.class);
registerAlias("_long", long.class);
registerAlias("_short", short.class);
registerAlias("_int", int.class);
registerAlias("_integer", int.class);
registerAlias("_double", double.class);
registerAlias("_float", float.class);
registerAlias("_boolean", boolean.class);
registerAlias("_byte[]", byte[].class);
registerAlias("_long[]", long[].class);
registerAlias("_short[]", short[].class);
registerAlias("_int[]", int[].class);
registerAlias("_integer[]", int[].class);
registerAlias("_double[]", double[].class);
registerAlias("_float[]", float[].class);
registerAlias("_boolean[]", boolean[].class);
registerAlias("date", Date.class);
registerAlias("decimal", BigDecimal.class);
registerAlias("bigdecimal", BigDecimal.class);
registerAlias("biginteger", BigInteger.class);
registerAlias("object", Object.class);
registerAlias("date[]", Date[].class);
registerAlias("decimal[]", BigDecimal[].class);
registerAlias("bigdecimal[]", BigDecimal[].class);
registerAlias("biginteger[]", BigInteger[].class);
registerAlias("object[]", Object[].class);
registerAlias("map", Map.class);
registerAlias("hashmap", HashMap.class);
registerAlias("list", List.class);
registerAlias("arraylist", ArrayList.class);
registerAlias("collection", Collection.class);
registerAlias("iterator", Iterator.class);
registerAlias("ResultSet", ResultSet.class);
}
对于上述这些类的别名，我们可以直接使用。
2.6 加载插件:pluginElement(root.evalNode(“plugins”))
几乎所有优秀的框架都会预留插件体系以便扩展，mybatis调用pluginElement(root.evalNode(“plugins”));加载mybatis插件，最常用的插件应该算是分页插件PageHelper了，再比如druid连接池提供的各种监控、拦截、预发检查功能，在使用其它连接池比如dbcp的时候，在不修改连接池源码的情况下，就可以借助mybatis的插件体系实现。加载插件的实现如下:
private void pluginElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
String interceptor = child.getStringAttribute("interceptor");
Properties properties = child.getChildrenAsProperties();
Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
interceptorInstance.setProperties(properties);
configuration.addInterceptor(interceptorInstance);
}
}
}
插件在具体实现的时候，采用的是拦截器模式，要注册为mybatis插件，必须实现org.apache.ibatis.plugin.Interceptor接口，每个插件可以有自己的属性。interceptor属性值既可以完整的类名，也可以是别名，只要别名在typealias中存在即可，如果启动时无法解析，会抛出ClassNotFound异常。实例化插件后，将设置插件的属性赋值给插件实现类的属性字段。后面会专门有一篇文章介绍。
2.7 加载对象工厂、创建对象包装器工厂、加载反射工厂
这些都属于比较高级的部分，平时基本用不到。后面会专门介绍这些。
2.8 加载环境配置environmentsElement
mybatis-config.xml文件中配置如下：
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/test"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
实现代码如下：
private void environmentsElement(XNode context) throws Exception {
if (context != null) {
if (environment == null) {
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()) {
String id = child.getStringAttribute("id");
// 查找匹配的env环境
if (isSpecifiedEnvironment(id)) {
// 事务管理器的配置
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
// 数据源的配置
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
DataSource dataSource = dsFactory.getDataSource();
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
事务管理器配置的代码实现：
private TransactionFactory transactionManagerElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
// 根据之前配置别名进行加载实例
TransactionFactory factory = (TransactionFactory) resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
}
throw new BuilderException("Environment declaration requires a TransactionFactory.");
}
数据源进行配置（DataSource）代码如下：
private DataSourceFactory dataSourceElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
}
throw new BuilderException("Environment declaration requires a DataSourceFactory.");
}
思路：
环境是MyBatis配置文件中最重要的部分之一，类似spring和maven的profile文件。同时给开发和生产环境配置不同的env环境，并根据不同的环境加载不同的配置，但是无论如果mybatis只能加载其中的一个配置。默认会使用default的环境。事务管理器和数据源类型在这里有JDBC和POOLED。前者主要用于简单JDBC模式，后者主要用于容器管理事务，一般使用JDBC事务管理方式。mybatis内置提供JNDI、POOLED、UNPOOLED三种数据源工厂，一般情况下使用POOLED数据源。
1.先是进行事务管理器配置（TransactionFactory ）。主要流程是根据配置的type类型，到类型别名中取到相应的class并进行实例化，即完成TransactionFactory的创建。需要说明的是：MyBatis中TransactionFactory的默认的类型有2种（JdbcTransactionFactory和ManagedTransactionFactory），并且这种类型在别名加载时就已经初始化进去了。
2.然后是对数据源进行配置（DataSource）。根据配置的连接池类型加载对应的dataSourceFactory工厂，然后获取相应的dataSource。然后调用Environment.Builder把factory和dataSource配置到Configuration中的env字段中去。
2.9 解析＜databaseldProvider＞节点
形如如下配置
<databaseIdProvider type="DB_VENDOR">
<property name="MySQL" value="mysql" />
<property name="Oracle" value="oracle" />
</databaseIdProvider>
对应实现代码如下:
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
private void databaseIdProviderElement(XNode context) throws Exception {
DatabaseIdProvider databaseIdProvider = null;
if (context != null) {
String type = context.getStringAttribute("type");
// awful patch to keep backward compatibility
if ("VENDOR".equals(type)) {
type = "DB_VENDOR";
}
Properties properties = context.getChildrenAsProperties();
databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
databaseIdProvider.setProperties(properties);
}
Environment environment = configuration.getEnvironment();
if (environment != null && databaseIdProvider != null) {
String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
configuration.setDatabaseId(databaseId);
}
}
思路：
根据配置的DB_VENDOR找到DatabaseIdProvider的DatabaseIdProvider的实现类（VendorDatabaseIdProvider），与此同时将property标签的集合进行注入工作。其次在根据已加载DataSource连接信息，调用VendorDatabaseIdProvider.getDatabaseId()获取数据库连接类型。
DatabaseIdProvider的补充
- 结构图
- 源码
补充：DatabaseIdProvider接口
public interface DatabaseIdProvider {
// 存储用户自定义的数据库配置
void setProperties(Properties p);
// 根据数据连接获得数据库产品的id标识
String getDatabaseId(DataSource dataSource) throws SQLException;
}
VendorDatabaseIdProvider实现类
public class VendorDatabaseIdProvider implements DatabaseIdProvider {
private static final Log log = LogFactory.getLog(VendorDatabaseIdProvider.class);
private Properties properties;
@Override
public String getDatabaseId(DataSource dataSource) {
if (dataSource == null) {
throw new NullPointerException("dataSource cannot be null");
}
try {
return getDatabaseName(dataSource);
} catch (Exception e) {
log.error("Could not get a databaseId from dataSource", e);
}
return null;
}
@Override
public void setProperties(Properties p) {
this.properties = p;
}
private String getDatabaseName(DataSource dataSource) throws SQLException {
// 解析DataSource连接的数据库产品名称
String productName = getDatabaseProductName(dataSource);
if (this.properties != null) {
// 根据databaseIdProvider标签下的子节点配置的数据库产品和databaseId之间的关系，确定最终的使用的databaseId
for (Map.Entry<Object, Object> property : properties.entrySet()) {
if (productName.contains((String) property.getKey())) {
return (String) property.getValue();
}
}
// no match, return null
// 找不到合适的database Id ，则返回null
return null;
}
return productName;
}
private String getDatabaseProductName(DataSource dataSource) throws SQLException {
Connection con = null;
try {
con = dataSource.getConnection();
DatabaseMetaData metaData = con.getMetaData();
return metaData.getDatabaseProductName();
} finally {
if (con != null) {
try {
con.close();
} catch (SQLException e) {
// ignored
}
}
}
}
}
DefaultDatabaseIdProvider 实现类（已过时，在这里不分析）
@Deprecated
public class DefaultDatabaseIdProvider extends VendorDatabaseIdProvider {
}
2.10 加载mapper文件mapperElement
形如如下的配置
<!-- 通过resource指定 -->
<mappers>
<mapper resource="UserMapper.xml"/>
</mappers>
<!-- 通过class指定接口，进而将接口对应的xml文件形成映射关系。不过使用这种方式必须保证:接口与mapper文件同名，不区分大小写。如UserMapper接口对应的xml文件名必须为UserMapper.xml -->
<mappers>
<mapper class="com.gyoomi.mapper.UserMapper"></mapper>
</mappers>
<!-- 通过直接url指定mapper文件位置 -->
<mappers>
<mapper url="file://"></mapper>
</mappers>
<!-- 通过直接指定包，自动扫描 -->
<mappers>
<package name="com.gyoomi"/>
</mappers>
对应代码如下
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) { // 处理mappers结点
if ("package".equals(child.getName())) { // 处理package结点得配置
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
// resource、url、class三者之间互斥
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
// 如果mapper节点指定了resouce或url。则创建XmlMapperBuilder对象，进行解析文件
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
// 如果mapper节点指定了resouce或url。则创建XmlMapperBuilder对象，进行解析文件
ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url == null && mapperClass != null) {
// 如果mapper指定了class，则直接加载类，向MapperRegister中进行注册
Class<?> mapperInterface = Resources.classForName(mapperClass);
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}
思路
分别package和mapper结点两种情况进行处理，最终都是调用MapperRegister中进行注册。