Mybatis源码浅析

源码阅读从测试类开始

public class MybatisTest {
    public static void main(String[] args) throws Exception {
        // 读取配置文件
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        // 创建SqlSessionFactory
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);//读取全局配置文件入口
        // 使用工厂生产sqlsession对象
        SqlSession sqlSession = factory.openSession();
        // 使用sqlsession创建UserDao接口代理对象
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        // 使用代理对象执行方法
        List<User> all = userDao.findAll();
        for (User user : all) {
            System.out.println(user);
        }
        // 释放资源
        sqlSession.close();
        in.close();
    }
}

一、根据SqlSessionFactory factory = builder.build(in)作为读取全局配置文件的入口

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());//根据传递的全局配置文件输入流使用xml解析器进行解析，在此处继续跟进此方法
    } 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.
      }
    }
  }

 public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    parseConfiguration(parser.evalNode("/configuration"));//在此处传递configration标签下的所有标签，在parseConfigration方法中继续解析，继续跟进方法
    return configuration;
  }

在此方法内解析全局配置文件的所有标签并保存到configration对象中

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

1、properties标签解析过程

private void propertiesElement(XNode context) throws Exception {
    if (context != null) {
      Properties defaults = context.getChildrenAsProperties(); // 此处首先将properties标签内的属性加载在defaults对象内（也就是如果直接将配置写在properties中会首先加载）
      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) {
        defaults.putAll(Resources.getResourceAsProperties(resource)); // 如果properties标签有resource属性，会根据resource读取配置文件然后将内容存储在defaults对象中
      } else if (url != null) {
        defaults.putAll(Resources.getUrlAsProperties(url)); // 如果properties标签有url属性，会根据url读取url资源，然后将读取内容存储在defaults对象中
      }
      Properties vars = configuration.getVariables(); // 此处为获取全局配置对象的Properties属性对象
      if (vars != null) {
        defaults.putAll(vars); // 将全局配置中的内容添加到defaults中
      }
      parser.setVariables(defaults); // 将添加properties内容的全局配置属性设置到解析器对象的variable属性中
      configuration.setVariables(defaults); // 将添加properties属性后的全局配置属性添加到configration对象的variable属性中
    }
  }

此处可以看出properties如果配置了多种方式配置，优先级顺序为 url配置方式>resource方式>直接在properties内设置值方式

2、settings解析过程

略

3、typeAliases标签解析过程（只看package方式源码，直接配置方式同package方式）

private void typeAliasesElement(XNode parent) {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) { // 如果typeAliases标签使用的是package属性方式
          String typeAliasPackage = child.getStringAttribute("name"); // 获取package的name属性（包名）
          configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage); // 调用registerAliases方法将包名传入，跟进方法源码
        } else { // 如果typeAliases别名直接在标签内配置方式
          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);
          }
        }
      }
    }
  }

public void registerAliases(String packageName, Class<?> superType){  // 该方法是根据传递的参数（包名）解析包下的所有类
    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
    resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
    Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();
    for(Class<?> type : typeSet){
      // Ignore inner classes and interfaces (including package-info.java)
      // Skip also inner classes. See issue #6
      if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {  // 排除匿名类、接口、成员类（只要实体类）
        registerAlias(type); // 将筛选出来的实体类调用registerAliases方法，跟进源码
      }
    }
  }

public void registerAlias(Class<?> type) {
    String alias = type.getSimpleName(); // 获取类名
    Alias aliasAnnotation = type.getAnnotation(Alias.class); // 获取该类的Alias注解
    if (aliasAnnotation != null) { // 如果实体类已经配置Alias注解
      alias = aliasAnnotation.value(); // 获取该注解的value值并赋值给alias变量
    } 
    registerAlias(alias, type); // 继续跟进方法
  }

 public void registerAlias(String alias, Class<?> value) {
    if (alias == null) {
      throw new TypeException("The parameter alias cannot be null");
    }
    // issue #748
    String key = alias.toLowerCase(Locale.ENGLISH); // 将传递的alias值变小写
    if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) { // 判断该别名与已经注册的别名有无冲突
      throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + TYPE_ALIASES.get(key).getName() + "'.");
    }
    TYPE_ALIASES.put(key, value); // 将别名和类对应设置在TYPE_ALIASES的map集合中
  }

4、plugins标签解析

略

5、objectFactory标签解析

略

6、objectWrapperFactory标签解析

略

7、reflectorFactory标签解析

略

8、environments标签解析

private void environmentsElement(XNode context) throws Exception {
    if (context != null) {
      if (environment == null) {
        environment = context.getStringAttribute("default"); // 获取environments的defaults的值，用来指定要启用哪个environment配置
      }
      for (XNode child : context.getChildren()) {
        String id = child.getStringAttribute("id"); // 获取每个environment的id属性值
        if (isSpecifiedEnvironment(id)) {  // 找到id值和environments的defaults值相同的environment配置
          TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager")); // 创建事务工厂，跟进源码
          DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource")); // 读取数据库配置文件生成数据库连接池工厂，跟进源码
          DataSource dataSource = dsFactory.getDataSource(); //返回数据库连接池
          Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
          configuration.setEnvironment(environmentBuilder.build()); // 将Environment对象传递给configration的environment属性
        }
      }
    }
  }

private TransactionFactory transactionManagerElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties props = context.getChildrenAsProperties();
      TransactionFactory factory = (TransactionFactory) resolveClass(type).newInstance();
      factory.setProperties(props);
      return factory; // 返回事务工厂对象
    }
    throw new BuilderException("Environment declaration requires a TransactionFactory.");
  }

private DataSourceFactory dataSourceElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties props = context.getChildrenAsProperties();
      DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
      factory.setProperties(props);
      return factory; // 返回数据库连接池对象
    }
    throw new BuilderException("Environment declaration requires a DataSourceFactory.");
  }

9、databaseIdProvider标签解析

略

10、typeHandlers标签解析

略

11、mappers标签解析

 private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) { // 如果mapper配置了package属性，根据包名解析
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage); // 将配置的mapper设置configration的mappers属性中，跟进源码
        } else {  // 如果配置了resource、url、class，根据这些参数进行解析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);
            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.");
          }
        }
      }
    }
  }

public void addMappers(String packageName, Class<?> superType) {
    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
    resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
    Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();
    for (Class<?> mapperClass : mapperSet) {
      addMapper(mapperClass); //遍历package下的所有类传递给addMapper方法，继续跟进
    }
  }

public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) { //如果是接口类型
      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(); // 解析每个接口 ，继续跟进
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

public void parse() {
    String resource = type.toString();
    if (!configuration.isResourceLoaded(resource)) { // 判断是否加载映射xml文件
      loadXmlResource(); 
      configuration.addLoadedResource(resource);
      assistant.setCurrentNamespace(type.getName());
      parseCache();
      parseCacheRef();
      Method[] methods = type.getMethods();
      for (Method method : methods) {
        try {
          // issue #237
          if (!method.isBridge()) {
            parseStatement(method); // 解析dao接口的方法 如果有注解则解析没有就不解析
          }
        } catch (IncompleteElementException e) {
          configuration.addIncompleteMethod(new MethodResolver(this, method));
        }
      }
    }
    parsePendingMethods();
  }

 二、解析mapper映射配置文件

在XMLMapperBuilder.java类中：

 public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
      configurationElement(parser.evalNode("/mapper")); //该方法就是解析mapper映射配置文件入口，跟进源码
      configuration.addLoadedResource(resource);
      bindMapperForNamespace();
    }

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

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")); // 在此处跟进源码查看select|insert|update|delete如何封装为MappedStatement对象
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
    }
  }

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))
          ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
    }

    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,  // 跟进此方法
        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(); // 构建MappedStatement对象
    configuration.addMappedStatement(statement);  // 将MappedStatement加入configration对象
    return statement;
  }

三、sql执行过程

 从测试方法的获取代理对象处跟踪即可...