mybatis源码分析——配置文件的解析

　　mybatis是一种半自动的orm对象关系模型框架，介于hibenate与jdbc之间，优势就是使用更加灵活，支持程序员手写sql

hibernate是自动生成的框架，不够灵活，jdbc完全手写，开发效率比较低，而mybatis在jdbc的基础上做了封装。

1：mybatis的简单使用

mysql数据库创建user表，字段name age

导入依赖maven

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.3.1</version>
        </dependency>

mybatis-config.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!-- 引入外部资源文件
        resource:默认引入classpath路径下的资源文件
        url：引入物理路径下的资源文件（如：d:\jdbc.properties）
     -->
    <properties resource="application.properties"></properties>
    <!-- 设置参数 -->
    <settings>
        <!--  开启驼峰匹配：完成经典的数据库命名到java属性的映射
                          相当于去掉数据中的名字的下划线，和java进行匹配
        -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
    <!-- 配置别名 -->
    <typeAliases>
        <!-- typeAlias:用来配置别名，方便映射文件使用，type:类的全限定类名,alias:别名 -->
        <typeAlias type="com.example.mybatis.model.User" alias="User"/>
    </typeAliases>
    <!--<plugins>
        <plugin interceptor="com.example.mybatis.plugin.MyFirstPlugin">
            <property name="someProperty" value="100"/>
        </plugin>
    </plugins>-->
    <!-- 配置环境：可以配置多个环境，default：配置某一个环境的唯一标识，表示默认使用哪个环境 -->
    <environments default="development">
        <!-- 配置环境,id:环境的唯一标识 -->
        <environment id="development">
            <!-- 事务管理器，type:使用jdbc的事务管理器 -->
            <transactionManager type="JDBC" />
            <!-- 数据源，type:池类型的数据源 -->
            <dataSource type="POOLED">
                <!-- 配置连接信息 -->
                <property name="driver" value="${jdbc.driverClass}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.username}" />
                <property name="password" value="${jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
    <!-- 配置映射文件：用来配置sql语句和结果集类型等 -->
    <mappers>
        <mapper resource="UserMapper.xml" />
    </mappers>
</configuration>

　　

userMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"      
"http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">

<mapper namespace="com.example.mybatis.mapper.UserMapper">

	<insert id="insert" parameterType="com.example.mybatis.model.User">
		insert into user (name,age) value(#{name},#{age})
	</insert>

	<select id="listUsers" resultType="com.example.mybatis.model.User">
		select * from user where name = #{name}
	</select>

</mapper>

　　

测试代码：

 public static void main(String[] args) throws IOException {
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        // 解析全局配置文件mybatis-config.xml
        SqlSessionFactory sqlSessionFactory = builder.build(reader);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> list =  userMapper.listUsers("hello105");
        System.out.println(list);

    }

　　

运行结果：

2：源码解析

 将xml文件读入内存，生成Reader对象

// 将mybatis-config的配置文件读入内存，生成字符流对象
Reader reader = Resources.getResourceAsReader("mybatis-config.xml");

　　

将字节流转换为字符流，并返回

 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;
  }

　　

解析xml文件，生成sqlSessionFactory对象，这里是比较的一步

         // 解析全局配置文件mybatis-config.xml
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = builder.build(reader);

　　

看一下build方法

  // 解析mybatis-config.xml配置文件
  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.
      }
    }
  }

　　

build方法里面首先是生成一个解析器XmlConfigBuilder，然后解析parse，最后封装build，解析的主要工作毋庸置疑是放在

parse方法中完成的，下面我们来看一下解析动作

 public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    // 解析mybatis-config配置文件
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

　　

首先会判断是否已经解析过，如果已经解析过，那么抛出异常，提示"每一个XMLConfigBuilder只能被解析一次"

如果之前没有被解析，那么开始解析工作，在parseConfiguration中完成，将解析后的数据封装到configuration对象中，

然后返回，现在我们来看一下parseConfiguration方法

xml中 /configuration节点作为入参传入：

// 解析mybatis-config配置文件
    parseConfiguration(parser.evalNode("/configuration"));

　　

private void parseConfiguration(XNode root) {
    try {
      Properties settings = settingsAsPropertiess(root.evalNode("settings"));
      //issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      loadCustomVfs(settings);
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectionFactoryElement(root.evalNode("reflectionFactory"));
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      // 解析环境 下的数据源信息
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      typeHandlerElement(root.evalNode("typeHandlers"));
      // 解析mapper.xml文件
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

　　

这里可以对照着mybatis-config.xml文件一起看，比较直观，因为这个方法就是解析这个xml文件，然后将解析的结果封装到configuration对象中

首先是解析properties节点，解析node上的resource属性，然后把解析的结果放到defaults这个集合中，最后设置到configuration对象上

  private void propertiesElement(XNode context) throws Exception {
    if (context != null) {
      Properties defaults = context.getChildrenAsProperties();
      // 获取Node节点上的resource属性
      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) {
        // 解析resource属性，并把解析的属性放到defaults里面
        defaults.putAll(Resources.getResourceAsProperties(resource));
      } else if (url != null) {
        defaults.putAll(Resources.getUrlAsProperties(url));
      }
      Properties vars = configuration.getVariables();
      if (vars != null) {
        defaults.putAll(vars);
      }
      parser.setVariables(defaults);
      // 将defaults属性设置到configuration对象中
      configuration.setVariables(defaults);
    }
  }

　　

看一下解析数据源：

// 解析环境 下的数据源信息
environmentsElement(root.evalNode("environments"));

　　

  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"));
          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());
        }
      }
    }
  }

　　

dataSourceElement方法将DataSource节点作为入参传入，将properties属性全部封装到 DataSourceFactory对象上，然后从数据源工厂中拿到数据源，设置到configuration对象
上


最重要的还是解析mapper.xml

      // 解析mapper.xml文件
      mapperElement(root.evalNode("mappers"));

　　

  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          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);
            configuration.addMapper(mapperInterface);
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }

　　

如果resource不为null，url为null，则进入这个方法的解析

mapperParser.parse();

  public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
      // 解析sql，生成mapperStatement
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      // 解析命名空间，绑定代理工厂
      bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingChacheRefs();
    parsePendingStatements();
  }

　　

下面看一下解析sql，生成mapperStatement的过程，方法

configurationElement(parser.evalNode("/mapper"))

  // 解析mapper.xml 里面的子元素
  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);
      cacheRefElement(context.evalNode("cache-ref"));
      cacheElement(context.evalNode("cache"));
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      sqlElement(context.evalNodes("/mapper/sql"));
      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
    }
  }

　　

解析mapper元素中子元素，sql元素、cache元素、resultMap元素，

select|insert|update|delete等元素

 buildStatementFromContext(context.evalNodes("select|insert|update|delete"));

　　

  public void parseStatementNode() {
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

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

    Integer fetchSize = context.getIntAttribute("fetchSize");
    Integer timeout = context.getIntAttribute("timeout");
    String parameterMap = context.getStringAttribute("parameterMap");
    String parameterType = context.getStringAttribute("parameterType");
    Class<?> parameterTypeClass = resolveClass(parameterType);
    String resultMap = context.getStringAttribute("resultMap");
    String resultType = context.getStringAttribute("resultType");
    String lang = context.getStringAttribute("lang");
    LanguageDriver langDriver = getLanguageDriver(lang);

    Class<?> resultTypeClass = resolveClass(resultType);
    String resultSetType = context.getStringAttribute("resultSetType");
    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);

    String nodeName = context.getNode().getNodeName();
    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
    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());

    // Parse selectKey after includes and remove them.
    processSelectKeyNodes(id, parameterTypeClass, langDriver);
    
    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    String resultSets = context.getStringAttribute("resultSets");
    String keyProperty = context.getStringAttribute("keyProperty");
    String keyColumn = context.getStringAttribute("keyColumn");
    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))
          ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
    }

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

　　

解析select insert  delete  update语句，将解析后的属性传给addMappedStatement方法，

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)
        .resulSets(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();
    configuration.addMappedStatement(statement);
    return statement;
  }

　　

将属性封装到MappedStatement对象上，然后将对象缓存到configuration中

再回过头来解析一下命名空间

      // 解析命名空间，绑定代理工厂
      bindMapperForNamespace();

　　

  private void bindMapperForNamespace() {
    String namespace = builderAssistant.getCurrentNamespace();
    if (namespace != null) {
      Class<?> boundType = null;
      try {
        boundType = Resources.classForName(namespace);
      } catch (ClassNotFoundException e) {
        //ignore, bound type is not required
      }
      if (boundType != null) {
        if (!configuration.hasMapper(boundType)) {
          // Spring may not know the real resource name so we set a flag
          // to prevent loading again this resource from the mapper interface
          // look at MapperAnnotationBuilder#loadXmlResource
          configuration.addLoadedResource("namespace:" + namespace);
          configuration.addMapper(boundType);
        }
      }
    }
  }

　

mapper.xml对应的命名空间就是mapper.java 的全路径名

<mapper namespace="com.example.mybatis.mapper.UserMapper">

　　

判断configuration对象中是否包含这个类型，如果没有则放入configuration中

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 {
        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);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

　　

　

 knownMappers.put(type, new MapperProxyFactory<T>(type));

将类型与通过类型创建的代理工厂放入mappers缓存中。


3：重点类分析

Configuration类：

这里面最重要的类就是Configuration，它对应mybatis-config.xml文件，将xml文件解析的内容缓存到Configuration对象中

MapperRegistry注册mappper用的，将命名空间与对应的代理工厂注册到这里

　缓存解析的Statement语句，key为sqlId的全路径名称，value为封装这个sql属性信息的对象

  XMLConfigBuilder类： 用来解析mybatis-config.xml文件

  XMLMapperBuilder类：用来解析Mapper.xml文件

总结：

1：类加载器读取mybatis-config.xml文件为字节流InputStream，然后将InputStream转换为字符流Reader

2：sqlSessionFactoryBuilder将解析Reader的工作委托给XMLConfigBuilder类处理

3：XMLConfigBuilder类又将解析mapper.xml的工作委托给XMLMapperBuilder类处理

4：XMLMapperBuilder类解析mapper.xml，sql、insert、update、select等元素，将解析后的数据封装到MapperStatement对象中，然后注册到MapperRegistry中

MapperRegistry是Configuration的属性，解析命名空间，将命名空间与Class对应的MapperProxyFactory映射缓存到mapperStatementMaps缓存中，以被后面使用，所以

所有的解析工作完成后，Configuration对象包含所有的mybatis-config.xml数据

SqlSessionFactory 用维护了Configuration对象

对应关系：

硬盘     内存对象

mybatis-config.xml          Configuration

mapper.xml sql属性        mappedStatements

mapper.xml 命名空间      mapperRegistry            

这一节的mybatis文件的解析就到这里了，下一节看mybatis的数据绑定