Mybatis 源码分析初始化

Mybatis使用时通过sqlsessionFactory获取一个sqlsession，而sqlsessionFactory是通过SqlSessionFactoryBuilder来构建一个sqlsessionFactory,通过传入的参数来构建。使用建造者模式，

InputStream configFile = new FileInputStream(
                "zjx-mybatis\\src\\main\\java\\com\\zjx\\mybatis\\demo\\mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configFile);

然后通过SqlSessionFactoryBuilder的build方法解析inputStream获取到mybatis-config.xml的详细配置。把mybatis-config.xml解析XPathParser

 public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
    //解析成为一个XpathParser然后把mybatis设置到configuration中
    this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
  }

  private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
    //创建一个configuration 
    super(new Configuration());
    ErrorContext.instance().resource("SQL Mapper Configuration");
    this.configuration.setVariables(props);
    this.parsed = false;
    this.environment = environment;
    this.parser = parser;
  }

初始化configuration并且把默认的类型别名注册进去

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);
  }

然后通过XMLConfigBuilder的parse方法解析xmlConfigBuilder,然后调用parseConfiguration方法

 public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      //解析XMLConfigBuilder 然后构建出一个SqlSessionFactory，XMLConfigBuilder解析调用parse方法解析为Configuration
      //SqlSessionFactory 为DefaultSqlSessionFactory
      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.
      }
    }
  }

 public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    //先把configuration标签解析成一个xnode对象然后解析里面的所有属性
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

  private void parseConfiguration(XNode root) {
    try {
    	//解析properties 然后设置到configuration中
      propertiesElement(root.evalNode("properties"));
    //解析settings
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      //解析typeAliases 然后设置到configuration中
      typeAliasesElement(root.evalNode("typeAliases"));
      //解析plugins 然后设置到configuration中
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      //然后设置到configuration中
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
    //解析environments 然后设置到configuration中
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //解析environments 然后设置到configuration中
     typeHandlerElement(root.evalNode("typeHandlers"));
     //解析mappers 然后设置到configuration中
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

调用propertiesElement解析properties 标签

//解析properties标签
  private void propertiesElement(XNode context) throws Exception {
    if (context != null) {
    	//获取所有的prop所有子节点然后把数据塞到Properties中
      Properties defaults = context.getChildrenAsProperties();
      String resource = context.getStringAttribute("resource");
      String url = context.getStringAttribute("url");
      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.");
      }
      
      if (resource != null) {//如果resource不为空那么把resource的数据放入到Properties中
        defaults.putAll(Resources.getResourceAsProperties(resource));
      } else if (url != null) {//如果url不为空那么把resource的数据放入到Properties中
        defaults.putAll(Resources.getUrlAsProperties(url));
      }
      Properties vars = configuration.getVariables();
      if (vars != null) {
        defaults.putAll(vars);
      }
      parser.setVariables(defaults);//把Properties的数据设置到XPathParser中
      configuration.setVariables(defaults);//把Properties的数据设置到configuration中
    }
  }

调用typeAliasesElement解析typeAliases标签

//解析类型别名
  private void typeAliasesElement(XNode parent) {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {//获取标签下的typeAliases 下的所有标签
        if ("package".equals(child.getName())) {//如果是package 类型别名注册到configuration中
          String typeAliasPackage = child.getStringAttribute("name");
          configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
        } else {//如果是typeAlias 类型别名注册到configuration中，把类型和别名对应起来注入到config总
          String alias = child.getStringAttribute("alias");
          String type = child.getStringAttribute("type");
          try {
            Class<?> clazz = Resources.classForName(type);
            if (alias == null) {
              typeAliasRegistry.registerAlias(clazz);
            } else {
              typeAliasRegistry.registerAlias(alias, clazz);
            }
          } catch (ClassNotFoundException e) {
            throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
          }
        }
      }
    }
  }

电泳pluginElement解析plugin

//解析plugins 然后设置到configuration中，然后添加到拦截器链中
  private void pluginElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        String interceptor = child.getStringAttribute("interceptor");
        Properties properties = child.getChildrenAsProperties();//获取拦截器配置的属性
        Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();//创建拦截器实例
        interceptorInstance.setProperties(properties);//设置属性
        configuration.addInterceptor(interceptorInstance);//添加到拦截器链中对执行操作进行拦截
      }
    }
  }

调用environmentsElement解析environments 

//设置环境
  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");
        if (isSpecifiedEnvironment(id)) {
          TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));//事物管理库
          DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));//数据源
          DataSource dataSource = dsFactory.getDataSource();
          Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
          configuration.setEnvironment(environmentBuilder.build());//设置环境
        }
      }
    }
  }

调用typeHandlerElement解析typeHandler

 //把typeHandler注册到configuration
  private void typeHandlerElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {//把typehandler注入configuration
          String typeHandlerPackage = child.getStringAttribute("name");
          typeHandlerRegistry.register(typeHandlerPackage);
        } else {
          String javaTypeName = child.getStringAttribute("javaType");//获取java类型
          String jdbcTypeName = child.getStringAttribute("jdbcType");//获取数据类型
          String handlerTypeName = child.getStringAttribute("handler");//获取handler
          Class<?> javaTypeClass = resolveClass(javaTypeName);
          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
          Class<?> typeHandlerClass = resolveClass(handlerTypeName);
          if (javaTypeClass != null) {//把typehandler注入configuration
            if (jdbcType == null) {
              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
            } else {
              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
            }
          } else {
            typeHandlerRegistry.register(typeHandlerClass);
          }
        }
      }
    }
  }

调用mapperElement解析mappers，把mapper解析成XMLMapperBuilder 然后解析数据，设置到configuration中 

 //解析mapper标签然后把mapper注册到configuration中
  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {//通过注解方式来读取信息
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);//把mapperpackage添加到configuration中然后在添加以后解析mapper
        } else {
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
          if (resource != null && url == null && mapperClass == null) {//获取resource然后解析mapper
            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) {//获取url然后解析mapper
            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) {//获取mapperClass然后解析mapper
            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.");
          }
        }
      }
    }
  }

调用configurationElement解析mapper文件

//解析mapper文件
  public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
    	//解析mapper标签然后返回xnode对象，然后进行处理
      configurationElement(parser.evalNode("/mapper"));
      //把解析的resource添加到configuration中然后避免重复加载
      configuration.addLoadedResource(resource);
      //绑定mapper和namespace
      bindMapperForNamespace();
    }
//没有解析的东西在这里解析？？？
    parsePendingResultMaps();
    parsePendingCacheRefs();
    parsePendingStatements();
  }

 //解析mapper文件
  private void configurationElement(XNode context) {
    try {
    	//获取namespace如果空抛出异常
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.equals("")) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      //把mapper包装成一个MapperBuilderAssistant 然后用来解析
      builderAssistant.setCurrentNamespace(namespace);
      //解析cache-ref 并且把两个namespace绑定起来 二级缓存
      cacheRefElement(context.evalNode("cache-ref"));
      //解析cache  二级缓存
      cacheElement(context.evalNode("cache"));
      //解析parameterMap，解析出所有的parameterMap 然后保存到MapperBuilderAssistant中
      //然后添加到configuration中的parameterMaps，<namespace+parameterMap.id,parameterMap>
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //解析resultMap ,保存到MapperBuilderAssistant中
      //resultMap添加到configuration中的resultMaps中保存类型为<namespace+resultMap.id,resultMap>
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //解析sql语句然后把sql语句保存到本地sqlFragments中<namespace+sql.id,sql>
      sqlElement(context.evalNodes("/mapper/sql"));
      //解析sql语句，吧sql语句解析成MappedStatement，然后把数据添加到configuration中
      //configuration存储数据为map<namespace+id,MappedStatement>
      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);
    }
  }

调用bindMapperForNamespace用于绑定类型和namespace

//绑定mapper和namespace
  private void bindMapperForNamespace() {
	  //获取namespace
    String namespace = builderAssistant.getCurrentNamespace();
    if (namespace != null) {
      Class<?> boundType = null;
      try {
    	  //获取namespace对应的接口
        boundType = Resources.classForName(namespace);
      } catch (ClassNotFoundException e) {
        //ignore, bound type is not required
      }
      	//如果是个类或者是个接口
      if (boundType != null) {
    	  //如果类型不为空且没有解析过该mapper
        if (!configuration.hasMapper(boundType)) {
        	//把namespace添加到已解析namespace中
          configuration.addLoadedResource("namespace:" + namespace);
          //把namespace对应的类型添加到configuration中
          configuration.addMapper(boundType);
        }
      }
    }
  }

全部解析完成以后，调用SqlSessionFactoryBuilder的build的方法，把所有解析的配置信息存放到configuration中然后赋值给默认的DefaultSqlSessionFactory中，在整个mybatis中configuration使用频率相当之高

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

通过代码获取一个SqlSession 调用sqlSessionFactory.openSession()方法，获取默认的sqlsession

 private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
    	//获取环境信息
      final Environment environment = configuration.getEnvironment();
      //获取事务管理器从环境信息
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      //创建一个事务管理器，，默认自动提交为false
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      //通过事务管理器和执行器获取一个执行器
      final Executor executor = configuration.newExecutor(tx, execType);
      //然后设置给sqlsession中
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

获取mapper文件，通过sqlSession调用getMapper方法获取mapper对象的动态代理对象，从configuration中获取对象

//获取mapper对象
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
	//从knownMappers获取MapperProxyFactory的mapper数据
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
    	//然后sqlsqssion放到mapper对象中然后获取
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }