原生Mybatis(查询)源码解析(一)

下一篇:原生Mybatis(查询)源码解析(二)

大家应该都知道Mybatis源码也是对Jbdc的再一次封装,不管怎么进行包装,还是会有获取链接、preparedStatement、封装参数、执行这些步骤的。

# 配置解析过程

String resource = "mybatis-config.xml";
//1.读取resources下面的mybatis-config.xml文件
InputStream inputStream = Resources.getResourceAsStream(resource);
//2.使用SqlSessionFactoryBuilder创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//3.通过sqlSessionFactory创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();

1.Resources.getResourceAsStream(resource)读取文件

public static InputStream getResourceAsStream(String resource) throws IOException {
    return getResourceAsStream(null, resource);
}

//loader赋值为null
public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException {
    InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader);
    if (in == null) {
      throw new IOException("Could not find resource " + resource);
    }
    return in;
  }

//classLoader为null
public InputStream getResourceAsStream(String resource, ClassLoader classLoader) {
    return getResourceAsStream(resource, getClassLoaders(classLoader));
}

//classLoader类加载
InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) {
    for (ClassLoader cl : classLoader) {
      if (null != cl) {

        //加载指定路径文件流
        InputStream returnValue = cl.getResourceAsStream(resource);

        // now, some class loaders want this leading "/", so we'll add it and try again if we didn't find the resource
        if (null == returnValue) {
          returnValue = cl.getResourceAsStream("/" + resource);
        }

        if (null != returnValue) {
          return returnValue;
        }
      }
    }
    return null;
  }

**总结:**主要是通过ClassLoader.getResourceAsStream()方法获取指定的classpath路径下的Resource

2.通过SqlSessionFactoryBuilder创建SqlSessionFactory

//SqlSessionFactoryBuilder是一个建造者模式
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

 public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
 }
//XMLConfigBuilder也是建造者模式
   public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

//接下来进入XMLConfigBuilder构造函数
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
    this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
  }

//接下来进入this后,初始化Configuration
  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;
  }

//其中parser.parse()负责解析xml,build(configuration)创建SqlSessionFactory
return build(parser.parse());

1.parser.parse()解析xml

  public Configuration parse() {
    //判断是否重复解析
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    //读取配置文件一级节点configuration
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

 private void parseConfiguration(XNode root) {
    try {
      //properties 标签,用来配置参数信息，比如最常见的数据库连接信息
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      loadCustomLogImpl(settings);
      //实体别名两种方式:1.指定单个实体;2.指定包
      typeAliasesElement(root.evalNode("typeAliases"));
      //插件
      pluginElement(root.evalNode("plugins"));
      //用来创建对象(数据库数据映射成java对象时)  
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      //数据库环境  
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //数据库类型和Java数据类型的转换  
      typeHandlerElement(root.evalNode("typeHandlers"));
      //这个是对数据库增删改查的解析  
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

总结:parseConfiguration完成的是解析configuration下的标签

 private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
          //解析<package name=""/>
        if ("package".equals(child.getName())) {
          String mapperPackage = child.getStringAttribute("name");
          //包路径存到mapperRegistry中  
          configuration.addMappers(mapperPackage);
        } else {
          //解析<mapper url="" class="" resource=""></mapper>  
          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);
            //读取Mapper.xml文件  
            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);
            configuration.addMapper(mapperInterface);
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }

总结: 通过解析configuration.xml文件,获取其中的Environment、Setting,重要的是将下的所有解析出来之后添加到Configuration,Configuration类似于配置中心,所有的配置信息都在这里。

2.mapperParser.parse()对 Mapper 映射器的解析

 public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
      //解析所有的子标签  
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      //把namespace（接口类型）和工厂类绑定起来  
      bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingCacheRefs();
    parsePendingStatements();
  }

  //这里面解析的是Mapper.xml的标签
  private void configurationElement(XNode context) {
    try {
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.equals("")) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      builderAssistant.setCurrentNamespace(namespace);
      //对其他命名空间缓存配置的引用  
      cacheRefElement(context.evalNode("cache-ref"));
      //对给定命名空间的缓存配置  
      cacheElement(context.evalNode("cache"));
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //是最复杂也是最强大的元素，用来描述如何从数据库结果集中来加载对象  
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //可被其他语句引用的可重用语句块  
      sqlElement(context.evalNodes("/mapper/sql"));
      //获得MappedStatement对象(增删改查标签) 
      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
    }
  }

//获得MappedStatement对象(增删改查标签) 
 private void buildStatementFromContext(List<XNode> list) {
    if (configuration.getDatabaseId() != null) {
      buildStatementFromContext(list, configuration.getDatabaseId());
    }
    buildStatementFromContext(list, null);
  }

//获得MappedStatement对象(增删改查标签)
 private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    //循环增删改查标签 
    for (XNode context : list) {
      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
        //解析insert/update/select/del中的标签  
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }

public void parseStatementNode() {
    //在命名空间中唯一的标识符,可以被用来引用这条语句
    String id = context.getStringAttribute("id");
    //数据库厂商标识
    String databaseId = context.getStringAttribute("databaseId");

    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
      return;
    }

    String nodeName = context.getNode().getNodeName();
    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
    //flushCache和useCache都和二级缓存有关
    //将其设置为true后,只要语句被调用,都会导致本地缓存和二级缓存被清空,默认值:false
    boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
    //将其设置为 true 后，将会导致本条语句的结果被二级缓存缓存起来，默认值：对 select 元素为 true
    boolean useCache = context.getBooleanAttribute("useCache", isSelect);
    boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);

    // Include Fragments before parsing
    XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
    includeParser.applyIncludes(context.getNode());
    //会传入这条语句的参数类的完全限定名或别名
    String parameterType = context.getStringAttribute("parameterType");
    Class<?> parameterTypeClass = resolveClass(parameterType);

    String lang = context.getStringAttribute("lang");
    LanguageDriver langDriver = getLanguageDriver(lang);

    // Parse selectKey after includes and remove them.
    processSelectKeyNodes(id, parameterTypeClass, langDriver);

    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    KeyGenerator keyGenerator;
    String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
    keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
    if (configuration.hasKeyGenerator(keyStatementId)) {
      keyGenerator = configuration.getKeyGenerator(keyStatementId);
    } else {
      keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
          configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
          ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
    }

    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
    Integer fetchSize = context.getIntAttribute("fetchSize");
    Integer timeout = context.getIntAttribute("timeout");
    String parameterMap = context.getStringAttribute("parameterMap");
    //从这条语句中返回的期望类型的类的完全限定名或别名
    String resultType = context.getStringAttribute("resultType");
    Class<?> resultTypeClass = resolveClass(resultType);
    //外部resultMap的命名引用
    String resultMap = context.getStringAttribute("resultMap");
    String resultSetType = context.getStringAttribute("resultSetType");
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
    String keyProperty = context.getStringAttribute("keyProperty");
    String keyColumn = context.getStringAttribute("keyColumn");
    String resultSets = context.getStringAttribute("resultSets");

    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
        resultSetTypeEnum, flushCache, useCache, resultOrdered,
        keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
  }

public MappedStatement addMappedStatement(
      String id,
      SqlSource sqlSource,
      StatementType statementType,
      SqlCommandType sqlCommandType,
      Integer fetchSize,
      Integer timeout,
      String parameterMap,
      Class<?> parameterType,
      String resultMap,
      Class<?> resultType,
      ResultSetType resultSetType,
      boolean flushCache,
      boolean useCache,
      boolean resultOrdered,
      KeyGenerator keyGenerator,
      String keyProperty,
      String keyColumn,
      String databaseId,
      LanguageDriver lang,
      String resultSets) {

    if (unresolvedCacheRef) {
      throw new IncompleteElementException("Cache-ref not yet resolved");
    }

    id = applyCurrentNamespace(id, false);
    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;

    MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)
        .resource(resource)
        .fetchSize(fetchSize)
        .timeout(timeout)
        .statementType(statementType)
        .keyGenerator(keyGenerator)
        .keyProperty(keyProperty)
        .keyColumn(keyColumn)
        .databaseId(databaseId)
        .lang(lang)
        .resultOrdered(resultOrdered)
        .resultSets(resultSets)
        .resultMaps(getStatementResultMaps(resultMap, resultType, id))
        .resultSetType(resultSetType)
        .flushCacheRequired(valueOrDefault(flushCache, !isSelect))
        .useCache(valueOrDefault(useCache, isSelect))
        .cache(currentCache);

    ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
    if (statementParameterMap != null) {
      statementBuilder.parameterMap(statementParameterMap);
    }

    MappedStatement statement = statementBuilder.build();
    //持有在configuration中
    configuration.addMappedStatement(statement);
    return statement;
  }

 public void addMappedStatement(MappedStatement ms) 
    //ms.getId = mapper.UserMapper.getUserById
    //ms = MappedStatement等于每一个增删改查的标签的里的数据
    mappedStatements.put(ms.getId(), ms);
  }

//最终存放到mappedStatements中,mappedStatements存放的是一个个的增删改查
protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection")
      .conflictMessageProducer((savedValue, targetValue) ->
          ". please check " + savedValue.getResource() + " and " + targetValue.getResource());

3.解析bindMapperForNamespace()方法

把 namespace（接口类型）和工厂类绑定起来

private void bindMapperForNamespace() {
    //当前Mapper的命名空间
    String namespace = builderAssistant.getCurrentNamespace();
    if (namespace != null) {
      Class<?> boundType = null;
      try {
        //interface mapper.UserMapper这种
        boundType = Resources.classForName(namespace);
      } catch (ClassNotFoundException e) {
      }
      if (boundType != null) {
        if (!configuration.hasMapper(boundType)) {
          configuration.addLoadedResource("namespace:" + namespace);
          configuration.addMapper(boundType);
        }
      }
    }
  }

 public <T> void addMapper(Class<T> type) {
    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 {
        //接口类型(key)->工厂类  
        knownMappers.put(type, new MapperProxyFactory<>(type));
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

4.(configuration)生成SqlSessionFactory对象

总结

XMLMapperBuilder.parse()方法,是对 Mapper 映射器的解析里面有两个方法：

1.configurationElement()解析所有的子标签,最终解析Mapper.xml中的insert/update/delete/select标签的id(全路径)组成key和整个标签和数据连接组成MappedStatement存放到Configuration中的 mappedStatements这个map里面。

2.bindMapperForNamespace()是把接口类型(interface mapper.UserMapper)和工厂类存到放MapperRegistry中的knownMappers里面。

##SqlSessionFactory的创建

public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

直接把Configuration当做参数,直接new一个DefaultSqlSessionFactory。