mybatis源码系列五-----加载mapper映射文件

mybatis是通过mapperElement()这个方法来加载mapper映射文件的。

private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        //如果配置的是package属性
        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");
          //配置的为resource属性
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            //读取文件字节流
            InputStream inputStream = Resources.getResourceAsStream(resource);
            //初始化解析器
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            //解析映射文件
            mapperParser.parse();
          } else if (resource == null && url != null && mapperClass == null) {                //配置的为url属性
            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) {            //配置的为class属性
            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.");
          }
        }
      }
    }
  }

这里主要是分析配置的为package属性，因为解析package属性对应的映射文件时最终还是调用的了与resource，class等一样的解析。

public void addMappers(String packageName) {
   mapperRegistry.addMappers(packageName);
}

public void addMappers(String packageName) {
   addMappers(packageName, Object.class);
}

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();
    
    //解析包下的class,其实这里mybatis解析的就是包下的类的全限定性类名.xmlz映射文件
    //后面会看到
    for (Class<?> mapperClass : mapperSet) {
      addMapper(mapperClass);
    }
 }
 
 //这边开始解析映射文件，parser.parse();
 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;                // 是否加载完成
      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
        loadCompleted = true;                        //解析完成
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }
  
  //最终执行该方法，这边是拼接包下的mapper文件
  public void parse() {
    String resource = type.toString();
    //判断mapper文件是否已经解析
    if (!configuration.isResourceLoaded(resource)) {
      //先根据全限定类名来拼接出mapper文件，然后解析
      loadXmlResource();
      //将解析后的mapper文件存入configuration中
      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);
          }
        } catch (IncompleteElementException e) {
          configuration.addIncompleteMethod(new MethodResolver(this, method));
        }
      }
    }
    parsePendingMethods();
  }
  
  //拼接mapper映射文件
  private void loadXmlResource() {
    // Spring may not know the real resource name so we check a flag
    // to prevent loading again a resource twice
    // this flag is set at XMLMapperBuilder#bindMapperForNamespace
    if (!configuration.isResourceLoaded("namespace:" + type.getName())) {
      String xmlResource = type.getName().replace('.', '/') + ".xml";
      InputStream inputStream = null;
      try {
        inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);
      } catch (IOException e) {
        // ignore, resource is not required
      }
      if (inputStream != null) {
        XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
        xmlParser.parse();
      }
    }
  }
  
  //这里最终的parse()解析方法，与resource，class属性解析的方法一致
  public void parse() {
    //判断mapper文件是否已经解析
    if (!configuration.isResourceLoaded(resource)) {
      //解析mapper映射文件
      configurationElement(parser.evalNode("/mapper"));
      //将解析后的mapper文件存入configuration中
      configuration.addLoadedResource(resource);
      //绑定已经解析后的命名空间
      bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingCacheRefs();
    parsePendingStatements();
  }
  
  //解析mapper映射文件
  private void configurationElement(XNode context) {
    try {
      //获取mapper映射文件中的命名空间
      String namespace = context.getStringAttribute("namespace");
      //命名空间不能为空
      if (namespace == null || namespace.equals("")) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      //将该命名空间赋值给mapper解析器助理，即告诉mapper解析器助理正在解析哪个mapper映射文件
      builderAssistant.setCurrentNamespace(namespace);
      //解析cache-ref节点
      cacheRefElement(context.evalNode("cache-ref"));
      //解析cache节点
      cacheElement(context.evalNode("cache"));
      //因为parameterMap可以配置多个，而且使用的是context.evalNodes方法，所以这边是"/mapper/parameterMap"
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //解析resultMap节点
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //解析sql节点
      sqlElement(context.evalNodes("/mapper/sql"));
      //解析select|insert|update|delete节点，注意context.evalNodes()方法，返回的是一个List集合。
      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);
    }
  }
  
  //解析select|insert|update|delete节点
  private void buildStatementFromContext(List<XNode> list) {
    if (configuration.getDatabaseId() != null) {
      buildStatementFromContext(list, configuration.getDatabaseId());
    }
    buildStatementFromContext(list, null);
  }

  //遍历所有声明的标签，逐个解析
  private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    for (XNode context : list) {
      //初始化标签解析器
      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
        //解析标签
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }
  
  //解析标签
  public void parseStatementNode() {
    //id
    String id = context.getStringAttribute("id");
    String databaseId = context.getStringAttribute("databaseId");

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

    //解析标签的一些属性
    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);

    //标签语句执行的返回值resultType
    Class<?> resultTypeClass = resolveClass(resultType);
    String resultSetType = context.getStringAttribute("resultSetType");
    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);

    //标签名，例如<select></select>标签，nodeName为select
    String nodeName = context.getNode().getNodeName();
    //sql类型是 sqlCommandType = SELECT
    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
    //isSelect = true;
    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.
    //处理selectKey 标签
    processSelectKeyNodes(id, parameterTypeClass, langDriver);
    
    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
    //在解析完<selectKey> 和 <include> 之后开始解析 SQL语句
    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
    String resultSets = context.getStringAttribute("resultSets");
    String keyProperty = context.getStringAttribute("keyProperty");
    String keyColumn = context.getStringAttribute("keyColumn");
    
    //接下来处理的是主键生成器
    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;
    }

    //mapper解析器助理创建MappedStatement实例对象，并将新建的实例对象添加到 configuration的 mappedStatements中，表示这个标签声明被解析过了。
    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
        resultSetTypeEnum, flushCache, useCache, resultOrdered, 
        keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
  }
  
  //解析，并创建MappedStatement对象
  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();
    configuration.addMappedStatement(statement);　　　　　　　　　　//statement保存到configuration中
    return statement;
  }

　　//看下configuration中如何保存statement的

　　public void addMappedStatement(MappedStatement ms) {
　　　　mappedStatements.put(ms.getId(), ms);　　　　　　//保存到一个map中mappedStatements
　　}

这边解析完成后， 绑定已经解析的命名空间bindMapperForNamespace()方法跟进下流程：

//这里将命名空间对应的类保存到configuration对象中
  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);                //注意这里，后面会用到
        }
      }
    }
  }

 

这里看下解析sql语句的方法SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);

public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
    SqlSource source = super.createSqlSource(configuration, script, parameterType);
    checkIsNotDynamic(source);
    return source;
  }
  
  public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
    //实例化解析器
    XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
    //解析sql语句
    return builder.parseScriptNode();
  }
  
  public SqlSource parseScriptNode() {
    MixedSqlNode rootSqlNode = parseDynamicTags(context);
    SqlSource sqlSource = null;
    if (isDynamic) {
      sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
    } else {
      sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
    }
    return sqlSource;
  }
  
  public RawSqlSource(Configuration configuration, SqlNode rootSqlNode, Class<?> parameterType) {
    this(configuration, getSql(configuration, rootSqlNode), parameterType);
  }
  
  private static String getSql(Configuration configuration, SqlNode rootSqlNode) {
    DynamicContext context = new DynamicContext(configuration, null);
    rootSqlNode.apply(context);
    return context.getSql();
  }
  
  public boolean apply(DynamicContext context) {
    for (SqlNode sqlNode : contents) {
      sqlNode.apply(context);
    }
    return true;
  }
  
  //返回解析后的sql语句
  public String getSql() {
    return sqlBuilder.toString().trim();
  }

  public RawSqlSource(Configuration configuration, String sql, Class<?> parameterType) {
    SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
    Class<?> clazz = parameterType == null ? Object.class : parameterType;
    sqlSource = sqlSourceParser.parse(sql, clazz, new HashMap<String, Object>());
  }