Mybatis源码简析

配置及流程

源码简析版本为mybatis 3.5.7

1.1 configuralion.xml

DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "https://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/all-demo?characterEncoding=utf8&useSSL=false"/>
        <property name="username" value="liuhuan"/>
        <property name="password" value="940920"/>
      dataSource>
    environment>
  environments>
  <mappers>
    <mapper resource="mapper/UserMapper.xml"/>
  mappers>
configuration>

1.2 mapper.xml

DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="user">
  <select id="findById" resultType="com.liuhuan.pojo.User" parameterType="long">
    select * from user where id = #{id}
  select>
mapper>

1.3 使用流程

整体流程从全局看

• 1.读取全局配置文件转为InputStream流对象
• 2.根据流对象创建SqlSessionFactory对象
• 3.根据SqlSessionFactory创建SqlSession对象
• 4.使用SqlSession进行语句操作

  @Test
  public void test1() throws IOException {
    // 获取sqlMapConfig.xml 转换成为InputStream流
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");

    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

    SqlSession sqlSession = sqlSessionFactory.openSession();

    User user = sqlSession.selectOne("user.findById", 1l);

    System.out.println(user);

    sqlSession.close();
  }

2 使用流程解析

2.1 读取配置文件

InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");

跟进去最后使用类加载器加载配置文件为流对象

 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;
  }

此处的加载器由mybatis创建

  ClassLoader[] getClassLoaders(ClassLoader classLoader) {
    return new ClassLoader[]{
        classLoader,
        defaultClassLoader,
        Thread.currentThread().getContextClassLoader(),
        getClass().getClassLoader(),
        systemClassLoader};
  }

2.2 构建SqlSessionFactory对象

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

调用SqlSessionFactoryBuilder的build方法，此方法为重载方法
第一个参数为流对象
第二个参数为配置的环境id
第三个参数为配置文件

  public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
  }

  public SqlSessionFactory build(InputStream inputStream, String environment) {
    return build(inputStream, environment, null);
  }

  public SqlSessionFactory build(InputStream inputStream, Properties properties) {
    return build(inputStream, null, properties);
  }

进入到最终调用的方法之中

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      // 构建者模式 XMLConfigBuilder 用来解析xml配置
      // 创建 XPathParser对象将inputStream解析成为document对象
      // 创建全局配置对象 Configuration
      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.
      }
    }
  }

首先是创建XMLConfigBuilder对象，用于后面对xml的解析工作,创建该对象的时候利用XPathParser首先对流对象进行解析，转换成document对象保存在XPathParser，并赋值给XMLConfigBuilder便于后续解析

  public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
    // XPathParser 基于java XPath解析器 用于解析Mybatis中的配置文件
    this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
  }

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

这里看一下Configuration对象，其中有很多别名以及对应的对象

  public Configuration() {
    // 注册事务工厂别名
    typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
    typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);

    // 注册数据源别名
    typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
    typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
    typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);

    // 注册缓存策略别名
    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);
  }

进入parse方法,首先判断配置文件是否被解析过，创建解析对象的时候赋值为false，同时判断之后设置为true，之后从根节点开始解析标签，并且封装到Configuration对象中

  public Configuration parse() {
    // 判断是否解析过配置文件
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    // 从根节点开始解析标签 封装到Configuration对象
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

这里主要看配置文件中的environments标签和mappers标签

  private void parseConfiguration(XNode root) {
    try {
      // issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      loadCustomLogImpl(settings);
      // 别名
      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);
    }
  }

解析environments标签，可以看到这里判断了environment 是否为空，表示前面在调用build方法的时候我们可以自己传入指定的环境，如果不传则获取默认的，根据标签配置的事务管理器以及数据源创建好我们的工厂对象，并且封装成为Environment对象保存到全局配置对象当中

  private void environmentsElement(XNode context) throws Exception {
    // 如果定义了environment标签
    if (context != null) {
      if (environment == null) {
        // 获取默认的如果定义了environment标签
        environment = context.getStringAttribute("default");
      }
      for (XNode child : context.getChildren()) {
        // 获取id属性值
        String id = child.getStringAttribute("id");
        // 判断 id的值和默认的值是否一致
        if (isSpecifiedEnvironment(id)) {
          //创建事务工厂对象
          TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
          // 创建数据源工厂对象
          DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
          DataSource dataSource = dsFactory.getDataSource();
          Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
          // 构建出environment 复制给全局configuration 对象
          configuration.setEnvironment(environmentBuilder.build());
          break;
        }
      }
    }
  }

解析mappers标签
根据配置的是package、resource、url、接口形式走不通的处理逻辑，这里配置的是resource，构建出XMLMapperBuilder 对象调用其parse方法

  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      // 获取mapper标签的子标签
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          // 获取mapper接口和mapper映射文件对应的package包名
          String mapperPackage = child.getStringAttribute("name");
          // 将mapper接口以及它的代理对象存储到一个map集合中，key为mapper接口类型，value为代理工厂
          configuration.addMappers(mapperPackage);
        } else {
          // 获取resource属性值
          String resource = child.getStringAttribute("resource");
          // 获取url属性值
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            // 将配置文件解析成为字节流
            try(InputStream inputStream = Resources.getResourceAsStream(resource)) {
              // 专门用来解析 mapper映射文件
              XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
              // 通过mapperParser 解析mapper映射文件
              mapperParser.parse();
            }
          } else if (resource == null && url != null && mapperClass == null) {
            // 解析配置了url的
            ErrorContext.instance().resource(url);
            try(InputStream inputStream = Resources.getUrlAsStream(url)){
              XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
              mapperParser.parse();
            }
          } else if (resource == null && url == null && mapperClass != null) {
            // 解析代理类的
            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.");
          }
        }
      }
    }
  }

首先判断是否解析过，如果没有则从mapper根节点开始解析

  public void parse() {
    // 判断映射文件是否解析过
    if (!configuration.isResourceLoaded(resource)) {
      // 从根节点开始解析
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      bindMapperForNamespace();
    }

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

进入configurationElement方法，这里重点关注对于select|insert|update|delete标签的解析

  private void configurationElement(XNode context) {
    try {
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.isEmpty()) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      // 构建MappedStatement的对象助手 设置当前的命名空间为namespace的值
      builderAssistant.setCurrentNamespace(namespace);
      // 解析 标签
      cacheRefElement(context.evalNode("cache-ref"));
      // 解析标签
      cacheElement(context.evalNode("cache"));
      // 解析  子标签
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      // 解析子标签
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      sqlElement(context.evalNodes("/mapper/sql"));
      // 解析select|insert|update|delete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);
    }
  }

继续跟进去，调到parseStatementNode()方法，这里根据标签的名称确认是增删改查哪种操作，这里也会对参数的别名进行处理，主要的方法langDriver.createSqlSource

  public void parseStatementNode() {
    // 获取statement的id值
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
      return;
    }
    // 获取节点名称 select delete 等
    String nodeName = context.getNode().getNodeName();
    // 根据名称 确认操作是哪种操作
    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
    // 是否查询语句
    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
    boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
    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());

    String parameterType = context.getStringAttribute("parameterType");
    // 别名处理
    Class<?> parameterTypeClass = resolveClass(parameterType);

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

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

    // Parse the SQL (pre:  and  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;
    }
    // 创建 SqlSource 解析sql 封装sql 参数绑定
    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");
    String resultType = context.getStringAttribute("resultType");
    Class<?> resultTypeClass = resolveClass(resultType);
    String resultMap = context.getStringAttribute("resultMap");
    String resultSetType = context.getStringAttribute("resultSetType");
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
    if (resultSetTypeEnum == null) {
      resultSetTypeEnum = configuration.getDefaultResultSetType();
    }
    String keyProperty = context.getStringAttribute("keyProperty");
    String keyColumn = context.getStringAttribute("keyColumn");
    String resultSets = context.getStringAttribute("resultSets");

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

进入到XMLLanguageDriver的createSqlSource方法,这里的构造方法会创建出一些常用标签的解析对象处理器

  public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
    XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
    return builder.parseScriptNode();
  }




  public XMLScriptBuilder(Configuration configuration, XNode context, Class<?> parameterType) {
    super(configuration);
    this.context = context;
    this.parameterType = parameterType;
    initNodeHandlerMap();
  }


  private void initNodeHandlerMap() {
    nodeHandlerMap.put("trim", new TrimHandler());
    nodeHandlerMap.put("where", new WhereHandler());
    nodeHandlerMap.put("set", new SetHandler());
    nodeHandlerMap.put("foreach", new ForEachHandler());
    nodeHandlerMap.put("if", new IfHandler());
    nodeHandlerMap.put("choose", new ChooseHandler());
    nodeHandlerMap.put("when", new IfHandler());
    nodeHandlerMap.put("otherwise", new OtherwiseHandler());
    nodeHandlerMap.put("bind", new BindHandler());
  }

进入到parseScriptNode方法当中，这里主要是解析标签，根据标签封装成为不通的SqlSource对象

  public SqlSource parseScriptNode() {
    // 带有 ${}的sql信息封装到TextSqlNode
    // 带有 #{}的sql信息封装到StaticTextNode
    MixedSqlNode rootSqlNode = parseDynamicTags(context);
    SqlSource sqlSource;
    // 包含${} 或者是动态sql  封装成为 DynamicSqlSource
    if (isDynamic) {
      sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
    } else {
      sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
    }
    return sqlSource;
  }

**进入parseDynamicTags方法，首先判断是否文本节点，也就是写的sql语句
例如 select * from user where id = #{id}，然后封装成为TextSqlNode对象，随后又判断是否动态，包含${}属于动态，点进去判断方法可以知道，此处不是，所以包装成为StaticTextSqlNode，最终封装在MixedSqlNode对象中返回
**

  protected MixedSqlNode parseDynamicTags(XNode node) {
    List<SqlNode> contents = new ArrayList<>();
    NodeList children = node.getNode().getChildNodes();
    for (int i = 0; i < children.getLength(); i++) {
      XNode child = node.newXNode(children.item(i));
      // 处理文本节点
      if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE || child.getNode().getNodeType() == Node.TEXT_NODE) {
        String data = child.getStringBody("");
        // 封装成为TextSqlNode
        TextSqlNode textSqlNode = new TextSqlNode(data);
        // 判断是否包含${}
        if (textSqlNode.isDynamic()) {
          contents.add(textSqlNode);
          isDynamic = true;
        } else {
          // 如果 不带${} 封装成为StaticTextSqlNode
          contents.add(new StaticTextSqlNode(data));
        }
      } else if (child.getNode().getNodeType() == Node.ELEMENT_NODE) { // issue #628
        String nodeName = child.getNode().getNodeName();
        //动态sql处理器
        NodeHandler handler = nodeHandlerMap.get(nodeName);
        if (handler == null) {
          throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");
        }
        handler.handleNode(child, contents);
        isDynamic = true;
      }
    }
    return new MixedSqlNode(contents);
  }


  public boolean isDynamic() {
    DynamicCheckerTokenParser checker = new DynamicCheckerTokenParser();
    GenericTokenParser parser = createParser(checker);
    parser.parse(text);
    return checker.isDynamic();
  }

  private GenericTokenParser createParser(TokenHandler handler) {
    return new GenericTokenParser("${", "}", handler);
  }

进入RawSqlSource的构造方法，这里会对sql再次进行处理，进入其parse方法，然后进入下面的parse方法

  public RawSqlSource(Configuration configuration, SqlNode rootSqlNode, Class<?> parameterType) {
    this(configuration, getSql(configuration, rootSqlNode), parameterType);
  }

  public RawSqlSource(Configuration configuration, String sql, Class<?> parameterType) {
    // 解析sql语句
    SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
    // 获取入参类型
    Class<?> clazz = parameterType == null ? Object.class : parameterType;
    sqlSource = sqlSourceParser.parse(sql, clazz, new HashMap<>());
  }


  public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {
    // 标记处理器
    ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);
    // 分词解析器
    GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);
    String sql;
    if (configuration.isShrinkWhitespacesInSql()) {
      sql = parser.parse(removeExtraWhitespaces(originalSql));
    } else {
      // 解析#{}
      sql = parser.parse(originalSql);
    }
    return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
  }

  public String parse(String text) {
    if (text == null || text.isEmpty()) {
      return "";
    }
    // search open token
    int start = text.indexOf(openToken);
    if (start == -1) {
      return text;
    }
    char[] src = text.toCharArray();
    int offset = 0;
    final StringBuilder builder = new StringBuilder();
    StringBuilder expression = null;
    do {
      if (start > 0 && src[start - 1] == '\\') {
        // this open token is escaped. remove the backslash and continue.
        builder.append(src, offset, start - offset - 1).append(openToken);
        offset = start + openToken.length();
      } else {
        // found open token. let's search close token.
        if (expression == null) {
          expression = new StringBuilder();
        } else {
          expression.setLength(0);
        }
        builder.append(src, offset, start - offset);
        offset = start + openToken.length();
        int end = text.indexOf(closeToken, offset);
        while (end > -1) {
          if (end > offset && src[end - 1] == '\\') {
            // this close token is escaped. remove the backslash and continue.
            expression.append(src, offset, end - offset - 1).append(closeToken);
            offset = end + closeToken.length();
            end = text.indexOf(closeToken, offset);
          } else {
            expression.append(src, offset, end - offset);
            break;
          }
        }
        if (end == -1) {
          // close token was not found.
          builder.append(src, start, src.length - start);
          offset = src.length;
        } else {
        	// 这里会对sql进行处理改成?
          builder.append(handler.handleToken(expression.toString()));
          offset = end + closeToken.length();
        }
      }
      start = text.indexOf(openToken, offset);
    } while (start > -1);
    if (offset < src.length) {
      builder.append(src, offset, src.length - offset);
    }
    return builder.toString();
  }

    public String handleToken(String content) {
      parameterMappings.add(buildParameterMapping(content));
      return "?";
    }

可以看到#{id} 已经被替换成了?

返回到上面parseStatementNode方法，在最后把解析出来的各种数据最后封装成为mappedStatement对象,并添加全局configuration对象当中

  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");
    }
    // 这里对id重新复制 改写成为 namespace +"." + statementId
    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();
    // 将MappedStatement存放到configuration key为namespace 的id+ .sql名称  user.findById
    configuration.addMappedStatement(statement);
    return statement;
  }

2.3 创建sqlSession对象

SqlSession sqlSession = sqlSessionFactory.openSession();

同样也是重载方法，跟进到方法openSessionFromDataSource,通过全局对象获取环境对象，然后根据环境创建事务工厂，根据数据源、隔离级别、是否自动提交创建出事务管理器,然后创建Ececutor执行器,执行器会是否开启缓存，会用CachingExecutor封装一层，这里也会将插件放到拦截链中

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      // 获取Environment对象
      final Environment environment = configuration.getEnvironment();
      // 获取事务工厂
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      // 根据级别和事务是否自动提交创建事务执行器 jdbc事务对象
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      // 根据执行器类型创建执行器对象
      final Executor executor = configuration.newExecutor(tx, execType);
      // 最后创建DefaultSqlSession对象
      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();
    }
  }




  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);
    }
    // 如果允许缓存 则会包装一层CachingExecutor
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    // 拦截器插件
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

Executor继承图

2.4执行查询

User user = sqlSession.selectOne("user.findById", 1l);

底层实际调用的是selectList,只是会根据结果进行返回处理

  public <T> T selectOne(String statement, Object parameter) {
    // Popular vote was to return null on 0 results and throw exception on too many.
    List<T> list = this.selectList(statement, parameter);
    if (list.size() == 1) {
      return list.get(0);
    } else if (list.size() > 1) {
      throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
    } else {
      return null;
    }
  }

跟到方法selectList,首先回根据startment获取mappedStatement对象，然后通过执行器执行query操作

  private <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
    try {
      // 根据传入的id 获取MappedStatement对象
      MappedStatement ms = configuration.getMappedStatement(statement);
      return executor.query(ms, wrapCollection(parameter), rowBounds, handler);
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

根据上面说的包装，进入到CacheExecutor执行器的query方法,首先生成缓存的key

  public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {

    BoundSql boundSql = ms.getBoundSql(parameterObject);
    // 生成缓存的key
    CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
    return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
  }

继续进去query方法,这里会处理二级缓存，看是否配置了对象，如果配置了，再根据配置是否要刷新决定是否清空缓存，如果二级缓存拿不到数据，则会继续继续query方法

  @Override
  public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
      throws SQLException {
    // 获取二级缓存
    Cache cache = ms.getCache();
    if (cache != null) {
      flushCacheIfRequired(ms);
      if (ms.isUseCache() && resultHandler == null) {
        ensureNoOutParams(ms, boundSql);
        @SuppressWarnings("unchecked")
          // 从二级缓存中获取数据
        List<E> list = (List<E>) tcm.getObject(cache, key);
        if (list == null) {
          // 二级缓存没有查询到数据
          list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
          // 结果缓存到二级缓存
          tcm.putObject(cache, key, list); // issue #578 and #116
        }
        return list;
      }
    }
    return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
  }

进入BaseExecutor执行器的方法,同样会判断是否需要清除缓存，如果从一级缓存拿不到数据，则会从数据库进行查询

  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
    ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
    if (closed) {
      throw new ExecutorException("Executor was closed.");
    }
    // 如果开启了FlushCacheRequired 则首先回清空缓存
    if (queryStack == 0 && ms.isFlushCacheRequired()) {
      clearLocalCache();
    }
    List<E> list;
    try {
      queryStack++;
      //从一级缓存获取
      list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
      if (list != null) {
        handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
      } else {
        // 从数据库查询
        list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
      }
    } finally {
      queryStack--;
    }
    if (queryStack == 0) {
      for (DeferredLoad deferredLoad : deferredLoads) {
        deferredLoad.load();
      }
      // issue #601
      deferredLoads.clear();
      if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
        // issue #482
        clearLocalCache();
      }
    }
    return list;
  }

进入queryFromDatabase，首先会进行缓存占位，之后会进行结果的查询

  private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
    List<E> list;
    // 一级缓存占位
    localCache.putObject(key, EXECUTION_PLACEHOLDER);
    try {
      // 查询结果
      list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
    } finally {
      // 移除缓存的key
      localCache.removeObject(key);
    }
    localCache.putObject(key, list);
    if (ms.getStatementType() == StatementType.CALLABLE) {
      localOutputParameterCache.putObject(key, parameter);
    }
    return list;
  }

进入到SimpleExecutor执行器，首先获取全局配置对象，构建StatementHandler 对象，这里构建出的是RoutingStatementHandler，同Executor一样也是包装

  public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    Statement stmt = null;
    try {
      // 获取全局配置对象
      Configuration configuration = ms.getConfiguration();
      // 构建一个StatementHandler对象
      StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
      stmt = prepareStatement(handler, ms.getStatementLog());

      return handler.query(stmt, resultHandler);
    } finally {
      closeStatement(stmt);
    }
  }

  public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    // 创建RoutingStatementHandler
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
  }

继续执行query，最终进入的PreparedStatementHandler,这里就会进行执行查询操作，然后处理返回的结果

  @Override
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    // 执行真正的处理
    ps.execute();
    return resultSetHandler.handleResultSets(ps);
  }

这里获取返回的resultMap, 实例配置的resultType，其实也是属于ResultMap对象，之后进入handleResultSet方法

 public List<Object> handleResultSets(Statement stmt) throws SQLException {
    ErrorContext.instance().activity("handling results").object(mappedStatement.getId());

    final List<Object> multipleResults = new ArrayList<>();

    int resultSetCount = 0;
    ResultSetWrapper rsw = getFirstResultSet(stmt);

    List<ResultMap> resultMaps = mappedStatement.getResultMaps();
    int resultMapCount = resultMaps.size();
    validateResultMapsCount(rsw, resultMapCount);
    while (rsw != null && resultMapCount > resultSetCount) {
      ResultMap resultMap = resultMaps.get(resultSetCount);
      handleResultSet(rsw, resultMap, multipleResults, null);
      rsw = getNextResultSet(stmt);
      cleanUpAfterHandlingResultSet();
      resultSetCount++;
    }

    String[] resultSets = mappedStatement.getResultSets();
    if (resultSets != null) {
      while (rsw != null && resultSetCount < resultSets.length) {
        ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
        if (parentMapping != null) {
          String nestedResultMapId = parentMapping.getNestedResultMapId();
          ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
          handleResultSet(rsw, resultMap, null, parentMapping);
        }
        rsw = getNextResultSet(stmt);
        cleanUpAfterHandlingResultSet();
        resultSetCount++;
      }
    }

    return collapseSingleResultList(multipleResults);
  }



  private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
    try {
      if (parentMapping != null) {
        handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
      } else {
        if (resultHandler == null) {
          DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
          //处理结果
          handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
          multipleResults.add(defaultResultHandler.getResultList());
        } else {
          handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
        }
      }
    } finally {
      // issue #228 (close resultsets)
      closeResultSet(rsw.getResultSet());
    }
  }

进入handleRowValues方法，继续进入,这里首先回根据分页，进行结果的提取，继续进入，在applyAutomaticMappings方法中会完成映射

  private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
      throws SQLException {
    DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
    ResultSet resultSet = rsw.getResultSet();
    // 根据分页提取结果
    skipRows(resultSet, rowBounds);
    while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
      ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
      Object rowValue = getRowValue(rsw, discriminatedResultMap, null);
      storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
    }
  }


  private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
    final ResultLoaderMap lazyLoader = new ResultLoaderMap();
    Object rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
    if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
      final MetaObject metaObject = configuration.newMetaObject(rowValue);
      boolean foundValues = this.useConstructorMappings;
      // 结果集是否自动映射  根据resultType判断
      if (shouldApplyAutomaticMappings(resultMap, false)) {
        foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
      }
      foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
      foundValues = lazyLoader.size() > 0 || foundValues;
      rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;
    }
    return rowValue;
  }

至此基本结束了