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整体加载过程
- mybatis-config.xml中可以在包(package)和class的方法让Mybatis加载一个Mapper
- 通过包的方式是从包加载所有的class,最条还是通过class方法来实现加载
- 加载过程中主要通过读取方法中的注解来生成MappedStatement对象，再加入到Configuration中。这个过程跟解析mapper.xml配置文件中的select/insert/update/delete节点的过程差不多。一个是从xml里读取信息，一个是从注解里读取信息。
- 通过注解生成的MappedStatement的Id生成规则为接口全限定名名加方法的名字，所以在定义Mapper接口类时千万不要重载方法，否则会发生预想不到的问题。
- Mapper接口中的只有包含如下八种注解中的一种才会被Mybatis解析成一个MappedStatement对象。
- Select/Insert/Update/Delete
- SelectProvider/InsertProvider/UpdateProvider/DeleteProvider
- Mybatis加载一个Mapper接口时会为其生成一个MapperProxyFactory对象，由这个对象来创建Mapper接口的实例。MapperProxyFactory这个类的实现在下一节详细分析。
Mapper的配置加载是从XmlConfigBuilder.mapperElement()方法中触发的
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
//通过package的方法
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
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) {
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) {
Class<?> mapperInterface = Resources.classForName(mapperClass);
//指定class的方式
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}通过package方式加载，最终也是找出所有符合条件的mapper类，再通过class的方法加载。
先来看configuration.addMaper()方法
public <T> void addMapper(Class<T> type) {
//最终是由MapperRegistry对象来完成加载的
mapperRegistry.addMapper(type);
} public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
//这里为一个Mapper生成一个代理工厂，这个代理工厂通过JDK动态代理生成一个对象，稍后再详细分析。
knownMappers.put(type, new MapperProxyFactory<T>(type));
// It's important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won't try.
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
//Mapper.xml是交由XMLMapperBuilder来解析的
//同样这里使用了MapperAnnotationBuilder来解析注解
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}MapperAnnotationBuilder.parse()方法
public void parse() {
String resource = type.toString();
if (!configuration.isResourceLoaded(resource)) {
//这里会先去加载相对应的mapper.xml配置文件
//也就是说解析UserDao注解时，如果发现有UserDao.xml配置文件会先加载UesrDao.xml配置文件
loadXmlResource();
configuration.addLoadedResource(resource);
assistant.setCurrentNamespace(type.getName());
parseCache();
parseCacheRef();
//获取class中所有的方法
Method[] methods = type.getMethods();
for (Method method : methods) {
try {
//解析方法
parseStatement(method);
} catch (IncompleteElementException e) {
configuration.addIncompleteMethod(new MethodResolver(this, method));
}
}
}
parsePendingMethods();
} //这个方法的功能就是读取方法的注解，生成一个MappedStatement对象，然后加入到Configuration中
void parseStatement(Method method) {
Class<?> parameterTypeClass = getParameterType(method);
LanguageDriver languageDriver = getLanguageDriver(method);
//从注解中获取一个SqlSource,之前已经分析过MappedStatement对应一个SqlSource对象，表示配置的Sql
SqlSource sqlSource = getSqlSourceFromAnnotations(method, parameterTypeClass, languageDriver);
//如果sqlSource为空，这个方法将直接返回
if (sqlSource != null) {
//读取方法中的Options注解
Options options = method.getAnnotation(Options.class);
//注意这个mappedStatementId的生成规则，Mybatis生成的Mapper代理对象也是根据这个规则来生成一个mappedStatementId，再去Configuration中加载MappedStatement的
final String mappedStatementId = type.getName() + "." + method.getName();
Integer fetchSize = null;
Integer timeout = null;
StatementType statementType = StatementType.PREPARED;
ResultSetType resultSetType = ResultSetType.FORWARD_ONLY;
SqlCommandType sqlCommandType = getSqlCommandType(method);
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
//注意这个
//这两个是设置二级缓存的，如果没有设置options注解，将使用如下默认值
//如果是update/insert/delete语句，就行里就会刷新缓存,select语句则不刷新
//如果是select语句是默认使用缓存的
boolean flushCache = !isSelect;
boolean useCache = isSelect;
KeyGenerator keyGenerator;
String keyProperty = "id";
String keyColumn = null;
//自动生成主键，一般在应用中比较少用
if (SqlCommandType.INSERT.equals(sqlCommandType) || SqlCommandType.UPDATE.equals(sqlCommandType)) {
// first check for SelectKey annotation - that overrides everything else
SelectKey selectKey = method.getAnnotation(SelectKey.class);
if (selectKey != null) {
keyGenerator = handleSelectKeyAnnotation(selectKey, mappedStatementId, getParameterType(method), languageDriver);
keyProperty = selectKey.keyProperty();
} else {
if (options == null) {
keyGenerator = configuration.isUseGeneratedKeys() ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
} else {
keyGenerator = options.useGeneratedKeys() ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
keyProperty = options.keyProperty();
keyColumn = options.keyColumn();
}
}
} else {
keyGenerator = new NoKeyGenerator();
}
if (options != null) {
flushCache = options.flushCache();
useCache = options.useCache();
fetchSize = options.fetchSize() > -1 || options.fetchSize() == Integer.MIN_VALUE ? options.fetchSize() : null; //issue #348
timeout = options.timeout() > -1 ? options.timeout() : null;
statementType = options.statementType();
resultSetType = options.resultSetType();
}
//获取对应的resultMap,还可以配置多个，用","分隔
String resultMapId = null;
ResultMap resultMapAnnotation = method.getAnnotation(ResultMap.class);
if (resultMapAnnotation != null) {
String[] resultMaps = resultMapAnnotation.value();
StringBuilder sb = new StringBuilder();
for (String resultMap : resultMaps) {
if (sb.length() > 0) sb.append(",");
sb.append(resultMap);
}
resultMapId = sb.toString();
} else if (isSelect) {
//如果没有配置resultMap，自动生成一个加入到Configuration中，就像Mapper.xml配置文件中只配置了resultType属性那样
resultMapId = parseResultMap(method);
}
//这里跟加载mapper.xml配置文件中一样，交由助手去生成一个MappedStatement并加入到Configuration中
assistant.addMappedStatement(
mappedStatementId,
sqlSource,
statementType,
sqlCommandType,
fetchSize,
timeout,
null, // ParameterMapID
parameterTypeClass,
resultMapId, // ResultMapID
getReturnType(method),
resultSetType,
flushCache,
useCache,
false, // TODO issue #577
keyGenerator,
keyProperty,
keyColumn,
null,
languageDriver,
null);
}
}再来看是怎么生成SqlSource对象的
private SqlSource getSqlSourceFromAnnotations(Method method, Class<?> parameterType, LanguageDriver languageDriver) {
try {
//获取方法的注解，Select/Update/Insert/Delete中的一种
Class<? extends Annotation> sqlAnnotationType = getSqlAnnotationType(method);
//获取方法的注解，SelectProvider/UpdateProvider/InsertProvider/DeleteProvider中的一种
Class<? extends Annotation> sqlProviderAnnotationType = getSqlProviderAnnotationType(method);
if (sqlAnnotationType != null) {
if (sqlProviderAnnotationType != null) {
//不支持两种注解同时存在
throw new BindingException("You cannot supply both a static SQL and SqlProvider to method named " + method.getName());
}
Annotation sqlAnnotation = method.getAnnotation(sqlAnnotationType);
//直接读取Select/Update/Insert/Delete中的sql内容
final String[] strings = (String[]) sqlAnnotation.getClass().getMethod("value").invoke(sqlAnnotation);
//通过sql创建一个SqlSource,这里的逻辑眼从mapper.xml文件读取里的逻辑差不多，不再讨论
return buildSqlSourceFromStrings(strings, parameterType, languageDriver);
} else if (sqlProviderAnnotationType != null) {
Annotation sqlProviderAnnotation = method.getAnnotation(sqlProviderAnnotationType);
//这个SqlSource主要是通过反射执行SelectProvider/UpdateProvider/InsertProvider/DeleteProvider的方法得到sql内容,也不再讨论
return new ProviderSqlSource(assistant.getConfiguration(), sqlProviderAnnotation);
}
return null;
} catch (Exception e) {
throw new BuilderException("Could not find value method on SQL annotation. Cause: " + e, e);
}
}