Mybatis3源码分析(20)-Mapper实现-配置加载

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整体加载过程

mybatis-config.xml中可以在包(package)和class的方法让Mybatis加载一个Mapper
通过包的方式是从包加载所有的class,最条还是通过class方法来实现加载
加载过程中主要通过读取方法中的注解来生成MappedStatement对象，再加入到Configuration中。这个过程跟解析mapper.xml配置文件中的select/insert/update/delete节点的过程差不多。一个是从xml里读取信息，一个是从注解里读取信息。
通过注解生成的MappedStatement的Id生成规则为接口全限定名名加方法的名字，所以在定义Mapper接口类时千万不要重载方法，否则会发生预想不到的问题。
Mapper接口中的只有包含如下八种注解中的一种才会被Mybatis解析成一个MappedStatement对象。
1. Select/Insert/Update/Delete
2. SelectProvider/InsertProvider/UpdateProvider/DeleteProvider
一个方法如果没有这些注解中的其中一个，执行时Mybatis会报MappedStatement找不到
Mybatis加载一个Mapper接口时会为其生成一个MapperProxyFactory对象，由这个对象来创建Mapper接口的实例。MapperProxyFactory这个类的实现在下一节详细分析。

Mapper的配置加载是从XmlConfigBuilder.mapperElement()方法中触发的

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

通过package方式加载，最终也是找出所有符合条件的mapper类，再通过class的方法加载。

先来看configuration.addMaper()方法

 public <T> void addMapper(Class<T> type) {    //最终是由MapperRegistry对象来完成加载的    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 {        //这里为一个Mapper生成一个代理工厂，这个代理工厂通过JDK动态代理生成一个对象，稍后再详细分析。        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);        //Mapper.xml是交由XMLMapperBuilder来解析的        //同样这里使用了MapperAnnotationBuilder来解析注解        parser.parse();        loadCompleted = true;      } finally {        if (!loadCompleted) {          knownMappers.remove(type);        }      }    }

MapperAnnotationBuilder.parse()方法

public void parse() {    String resource = type.toString();    if (!configuration.isResourceLoaded(resource)) {      //这里会先去加载相对应的mapper.xml配置文件      //也就是说解析UserDao注解时，如果发现有UserDao.xml配置文件会先加载UesrDao.xml配置文件      loadXmlResource();      configuration.addLoadedResource(resource);      assistant.setCurrentNamespace(type.getName());      parseCache();      parseCacheRef();      //获取class中所有的方法      Method[] methods = type.getMethods();      for (Method method : methods) {        try {          //解析方法          parseStatement(method);        } catch (IncompleteElementException e) {          configuration.addIncompleteMethod(new MethodResolver(this, method));        }      }    }    parsePendingMethods();  }

  //这个方法的功能就是读取方法的注解，生成一个MappedStatement对象，然后加入到Configuration中  void parseStatement(Method method) {    Class<?> parameterTypeClass = getParameterType(method);    LanguageDriver languageDriver = getLanguageDriver(method);    //从注解中获取一个SqlSource,之前已经分析过MappedStatement对应一个SqlSource对象，表示配置的Sql    SqlSource sqlSource = getSqlSourceFromAnnotations(method, parameterTypeClass, languageDriver);    //如果sqlSource为空，这个方法将直接返回    if (sqlSource != null) {      //读取方法中的Options注解      Options options = method.getAnnotation(Options.class);      //注意这个mappedStatementId的生成规则，Mybatis生成的Mapper代理对象也是根据这个规则来生成一个mappedStatementId，再去Configuration中加载MappedStatement的      final String mappedStatementId = type.getName() + "." + method.getName();      Integer fetchSize = null;      Integer timeout = null;      StatementType statementType = StatementType.PREPARED;      ResultSetType resultSetType = ResultSetType.FORWARD_ONLY;      SqlCommandType sqlCommandType = getSqlCommandType(method);      boolean isSelect = sqlCommandType == SqlCommandType.SELECT;      //注意这个      //这两个是设置二级缓存的，如果没有设置options注解，将使用如下默认值      //如果是update/insert/delete语句，就行里就会刷新缓存,select语句则不刷新      //如果是select语句是默认使用缓存的      boolean flushCache = !isSelect;      boolean useCache = isSelect;      KeyGenerator keyGenerator;      String keyProperty = "id";      String keyColumn = null;      //自动生成主键，一般在应用中比较少用      if (SqlCommandType.INSERT.equals(sqlCommandType) || SqlCommandType.UPDATE.equals(sqlCommandType)) {        // first check for SelectKey annotation - that overrides everything else        SelectKey selectKey = method.getAnnotation(SelectKey.class);        if (selectKey != null) {          keyGenerator = handleSelectKeyAnnotation(selectKey, mappedStatementId, getParameterType(method), languageDriver);          keyProperty = selectKey.keyProperty();        } else {          if (options == null) {            keyGenerator = configuration.isUseGeneratedKeys() ? new Jdbc3KeyGenerator() : new NoKeyGenerator();          } else {            keyGenerator = options.useGeneratedKeys() ? new Jdbc3KeyGenerator() : new NoKeyGenerator();            keyProperty = options.keyProperty();            keyColumn = options.keyColumn();          }        }      } else {        keyGenerator = new NoKeyGenerator();      }      if (options != null) {        flushCache = options.flushCache();        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();        resultSetType = options.resultSetType();      }           //获取对应的resultMap,还可以配置多个，用","分隔      String resultMapId = null;      ResultMap resultMapAnnotation = method.getAnnotation(ResultMap.class);      if (resultMapAnnotation != null) {        String[] resultMaps = resultMapAnnotation.value();        StringBuilder sb = new StringBuilder();        for (String resultMap : resultMaps) {          if (sb.length() > 0) sb.append(",");          sb.append(resultMap);        }        resultMapId = sb.toString();      } else if (isSelect) {        //如果没有配置resultMap，自动生成一个加入到Configuration中，就像Mapper.xml配置文件中只配置了resultType属性那样        resultMapId = parseResultMap(method);      }            //这里跟加载mapper.xml配置文件中一样，交由助手去生成一个MappedStatement并加入到Configuration中      assistant.addMappedStatement(          mappedStatementId,          sqlSource,          statementType,          sqlCommandType,          fetchSize,          timeout,          null,                             // ParameterMapID          parameterTypeClass,          resultMapId,    // ResultMapID          getReturnType(method),          resultSetType,          flushCache,          useCache,          false, // TODO issue #577          keyGenerator,          keyProperty,          keyColumn,          null,          languageDriver,          null);    }  }

再来看是怎么生成SqlSource对象的

 private SqlSource getSqlSourceFromAnnotations(Method method, Class<?> parameterType, LanguageDriver languageDriver) {    try {      //获取方法的注解，Select/Update/Insert/Delete中的一种      Class<? extends Annotation> sqlAnnotationType = getSqlAnnotationType(method);      //获取方法的注解，SelectProvider/UpdateProvider/InsertProvider/DeleteProvider中的一种      Class<? extends Annotation> sqlProviderAnnotationType = getSqlProviderAnnotationType(method);      if (sqlAnnotationType != null) {        if (sqlProviderAnnotationType != null) {          //不支持两种注解同时存在          throw new BindingException("You cannot supply both a static SQL and SqlProvider to method named " + method.getName());        }                Annotation sqlAnnotation = method.getAnnotation(sqlAnnotationType);        //直接读取Select/Update/Insert/Delete中的sql内容        final String[] strings = (String[]) sqlAnnotation.getClass().getMethod("value").invoke(sqlAnnotation);        //通过sql创建一个SqlSource,这里的逻辑眼从mapper.xml文件读取里的逻辑差不多，不再讨论        return buildSqlSourceFromStrings(strings, parameterType, languageDriver);      } else if (sqlProviderAnnotationType != null) {        Annotation sqlProviderAnnotation = method.getAnnotation(sqlProviderAnnotationType);        //这个SqlSource主要是通过反射执行SelectProvider/UpdateProvider/InsertProvider/DeleteProvider的方法得到sql内容,也不再讨论        return new ProviderSqlSource(assistant.getConfiguration(), sqlProviderAnnotation);      }      return null;    } catch (Exception e) {      throw new BuilderException("Could not find value method on SQL annotation.  Cause: " + e, e);    }  }

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