Mybatis3源码笔记（五）mapperElement

1.四种解析mapper方式 : package,resource,url,class。

  <mappers>
    <mapper resource="org/apache/ibatis/builder/BlogMapper.xml"/>
    <mapper url="file:./src/test/java/org/apache/ibatis/builder/NestedBlogMapper.xml"/>
    <mapper class="org.apache.ibatis.builder.CachedAuthorMapper"/>
    <package name="org.apache.ibatis.builder.mapper"/>
  </mappers>

private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        //package引入
        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");
          //resource引入
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            try (InputStream inputStream = Resources.getResourceAsStream(resource)) {
              XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
              mapperParser.parse();
            }
          } else if (resource == null && url != null && mapperClass == null) {
            //url引入
            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) {
            //mapperClass引入
            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.");
          }
        }
      }
    }
  }

2.跟一下package引入。

  public <T> void addMapper(Class<T> type) {
    //必须是接口
    if (type.isInterface()) {
      //重复性检查
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<>(type));
        //解析Mapper接口
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

  public void parse() {
    String resource = type.toString();
    //判断该resource有没有引入
    if (!configuration.isResourceLoaded(resource)) {
      //加载该命名空间下对应的xml
      loadXmlResource();
      configuration.addLoadedResource(resource);
      assistant.setCurrentNamespace(type.getName());
      //解析二级缓存注解CacheNamespace
      parseCache();
      //解析二级缓存注解CacheNamespaceRef
      parseCacheRef();
      for (Method method : type.getMethods()) {
        //检查下method类型，不能是桥接方法和接口中的默认方法
        if (!canHaveStatement(method)) {
          continue;
        }
        //select操作解析@select,@SelectProvider注释方法中的带有@ResultMap的方法
        if (getAnnotationWrapper(method, false, Select.class, SelectProvider.class).isPresent()
            && method.getAnnotation(ResultMap.class) == null) {
          parseResultMap(method);
        }
        try {
          //解析Statement
          parseStatement(method);
        } catch (IncompleteElementException e) {
          configuration.addIncompleteMethod(new MethodResolver(this, method));
        }
      }
    }
    //解析IncompleteMethod，解析失败的方法。
    parsePendingMethods();
  }

 void parseStatement(Method method) {
     //取得方法的参数类型
    final Class<?> parameterTypeClass = getParameterType(method);
    //根据@Lang取得方法的LanguageDriver,默认是XMLLanguageDriver
    final LanguageDriver languageDriver = getLanguageDriver(method);
    //解析所有合法的statement注解，譬如@Select, @Update, @Insert, @Delete, @SelectProvider...
    getAnnotationWrapper(method, true, statementAnnotationTypes).ifPresent(statementAnnotation -> {
      //生成SqlSource
      final SqlSource sqlSource = buildSqlSource(statementAnnotation.getAnnotation(), parameterTypeClass, languageDriver, method);
      final SqlCommandType sqlCommandType = statementAnnotation.getSqlCommandType();
      //取得@Options注解
      final Options options = getAnnotationWrapper(method, false, Options.class).map(x -> (Options) x.getAnnotation()).orElse(null);
      //设置mappedStatementId，方法的全路径
      final String mappedStatementId = type.getName() + "." + method.getName();

      final KeyGenerator keyGenerator;
      String keyProperty = null;
      String keyColumn = null;
      //插入和更新需要涉及到主键自动生成
      if (SqlCommandType.INSERT.equals(sqlCommandType) || SqlCommandType.UPDATE.equals(sqlCommandType)) {
        // @SelectKey注解生成主键
        SelectKey selectKey = getAnnotationWrapper(method, false, SelectKey.class).map(x -> (SelectKey) x.getAnnotation()).orElse(null);
        if (selectKey != null) {
          keyGenerator = handleSelectKeyAnnotation(selectKey, mappedStatementId, getParameterType(method), languageDriver);
          keyProperty = selectKey.keyProperty();
        } else if (options == null) {
          //默认模式
          keyGenerator = configuration.isUseGeneratedKeys() ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
        } else {
          //根据@Options中的value值实现自定义设置
          keyGenerator = options.useGeneratedKeys() ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
          keyProperty = options.keyProperty();
          keyColumn = options.keyColumn();
        }
      } else {
        keyGenerator = NoKeyGenerator.INSTANCE;
      }

      Integer fetchSize = null;
      Integer timeout = null;
      StatementType statementType = StatementType.PREPARED;
      ResultSetType resultSetType = configuration.getDefaultResultSetType();
      boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
      boolean flushCache = !isSelect;
      boolean useCache = isSelect;
      if (options != null) {
        //设置对应的options
        if (FlushCachePolicy.TRUE.equals(options.flushCache())) {
          flushCache = true;
        } else if (FlushCachePolicy.FALSE.equals(options.flushCache())) {
          flushCache = false;
        }
        useCache = options.useCache();
        fetchSize = options.fetchSize() > -1 || options.fetchSize() == Integer.MIN_VALUE ? options.fetchSize() : null; //issue #348
        timeout = options.timeout() > -1 ? options.timeout() : null;
        statementType = options.statementType();
        if (options.resultSetType() != ResultSetType.DEFAULT) {
          resultSetType = options.resultSetType();
        }
      }

      String resultMapId = null;
      if (isSelect) {
        ResultMap resultMapAnnotation = method.getAnnotation(ResultMap.class);
        if (resultMapAnnotation != null) {
          //根据 @ResultMap({ "xx", "xxx" })设置resultMapId
          resultMapId = String.join(",", resultMapAnnotation.value());
        } else {
          //没配置@ResultMap则走generateResultMapName方法生成resultMapId（方法的详细路径+“-”+参数类型）
          resultMapId = generateResultMapName(method);
        }
      }
      //生成Statement`
      assistant.addMappedStatement(
        mappedStatementId,
        sqlSource,
        statementType,
        sqlCommandType,
        fetchSize,
        timeout,
        // ParameterMapID
        null,
        parameterTypeClass,
        resultMapId,
        getReturnType(method),
        resultSetType,
        flushCache,
        useCache,
        // TODO gcode issue #577
        false,
        keyGenerator,
        keyProperty,
        keyColumn,
        statementAnnotation.getDatabaseId(),
        languageDriver,
        // ResultSets
        options != null ? nullOrEmpty(options.resultSets()) : null);
    });
  }

3.其它的引入方式resource和url方式，就是先解析一波xml文件，大同小异。

  public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
      //解析mapper.xml文件
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      //解析对应空间下的mapper接口（跟上面的package方法一样的解析过程）
      bindMapperForNamespace();
    }

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

  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");
      }
      //设置命名空间
      builderAssistant.setCurrentNamespace(namespace);
      //设置二级缓存
      cacheRefElement(context.evalNode("cache-ref"));
      cacheElement(context.evalNode("cache"));
      //解析parameterMap
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      //解析resultMap
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      //解析sql片段
      sqlElement(context.evalNodes("/mapper/sql"));
      //解析真正的sql语句
      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);
    }
  }

mapper的解析分注解如@Select和xml两种解析，看代码我们可以看出来，同一个方法都是先找xml，后分析注解，根据configuration.isResourceLoaded来判断是否已经解析，防止重复解析。