Configuration--mappers--addMappers(三-8-1)

本篇文章,我们来讲讲,当mapper标签加载的是一个类时,Configuration的addMappers方法的解析过程.

mapper标签引用类的情况:

<mappers>  <mapper class="org.mybatis.builder.AuthorMapper"/>  <package name="org.mybatis.builder"/></mappers>

可以看出,一种是单独引用一个类,一种是一次性引入一个包下所有类.而addMappers方法有两种形式的重载:

  // Configuration中的成员变量MapperRegistry  protected MapperRegistry mapperRegistry = new MapperRegistry(this);  // 一次加载一个包下的类  public void addMappers(String packageName) {    mapperRegistry.addMappers(packageName);  }  // 一次加载一个类  public <T> void addMapper(Class<T> type) {    mapperRegistry.addMapper(type);  }

从上述代码可以看出,Configuration中实际是使用了MapperRegistry的addMappers方法,我们先来看MapperRegistry中一次加载一个包下所有类的方法:

  public void addMappers(String packageName) {    addMappers(packageName, Object.class);  }  public void addMappers(String packageName, Class<?> superType) {    // 找到该包下所有的Java类    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();    resolverUtil.find(new ResolverUtil.IsA(superType), packageName);    Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();    // 循环调用addMapper(Class<T> type)    for (Class<?> mapperClass : mapperSet) {      addMapper(mapperClass);    }  }

从上述代码中,我们可以看出,加载一个包下所有的类,最后还是循环调用一次加载一个类的方法:

  public <T> void addMapper(Class<T> type) {    // 该类必须为接口    if (type.isInterface()) {      // 检测该类是否已经被加载过      if (hasMapper(type)) {        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");      }      boolean loadCompleted = false;      try {        // MapperProxyFactory是Mapper的代理,之后用到的时候我们在讲        knownMappers.put(type, new MapperProxyFactory<T>(type));        // 构造一个MapperAnnotationBuilder去解析这个类        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);        parser.parse();        loadCompleted = true;      } finally {        // 若上面加载时出错,则将该类移除        if (!loadCompleted) {          knownMappers.remove(type);        }      }    }  }  public <T> boolean hasMapper(Class<T> type) {    // knownMappers为MapperRegistry的一个Map结构,用来保存已经加载过的类信息和代理工厂的对应关系    return knownMappers.containsKey(type);  }  private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();

从上述代码可以看出,对具体类的解析是在MapperAnnotationBuilder中完成的,我们先来看看MapperAnnotationBuilder的构造方法:

  private final Set<Class<? extends Annotation>> sqlAnnotationTypes = new HashSet<>();  private final Set<Class<? extends Annotation>> sqlProviderAnnotationTypes = new HashSet<>();  public MapperAnnotationBuilder(Configuration configuration, Class<?> type) {    String resource = type.getName().replace('.', '/') + ".java (best guess)";    this.assistant = new MapperBuilderAssistant(configuration, resource);    this.configuration = configuration;    this.type = type;    sqlAnnotationTypes.add(Select.class);    sqlAnnotationTypes.add(Insert.class);    sqlAnnotationTypes.add(Update.class);    sqlAnnotationTypes.add(Delete.class);    sqlProviderAnnotationTypes.add(SelectProvider.class);    sqlProviderAnnotationTypes.add(InsertProvider.class);    sqlProviderAnnotationTypes.add(UpdateProvider.class);    sqlProviderAnnotationTypes.add(DeleteProvider.class);  }

接下来看比较重要的parse()方法:

  public void parse() {    String resource = type.toString();    // 是否已经加载过该resource(值形式类似于为:interface org.tree.study.mybatis.dao.UserDao)    if (!configuration.isResourceLoaded(resource)) {      // 加载类对应的xml文件      loadXmlResource();      // 将该resource加入已经加载过的Set中      configuration.addLoadedResource(resource);      // 设置命名空间      assistant.setCurrentNamespace(type.getName());      // 加载CacheNamespace注解      parseCache();      // 加载CacheNamespaceRef注解      parseCacheRef();      // 加载类中所有的方法      Method[] methods = type.getMethods();      for (Method method : methods) {        try {          // 解析方法          parseStatement(method);        } catch (IncompleteElementException e) {          // 将异常解析的方法加入一个List中          configuration.addIncompleteMethod(new MethodResolver(this, method));        }      }    }    // 重新处理异常解析的方法    parsePendingMethods();  }

上述代码逻辑比较复杂,但是总的来说,核心是去加载xml文件和加载该类上的注解(这也证明mybatis支持xml配置和注解配置两种方式).

我们先来看loadXmlResource()方法:

  private void loadXmlResource() {    // 看是否已经加载过该xml文件    if (!configuration.isResourceLoaded("namespace:" + type.getName())) {      // 从这里我们可以看出,若是要使用加载类的方法,xml文件的路径需要和类的包名路径一致,并且xml文件名要和类名一致(如:org.tree.study.mybatis.dao.UserDao对应org/tree/study/mybatis/dao/UserDao.xml)      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) {        // 从这里我们看出,加载xml文件时,使用了XMLMapperBuilder,这正是我们要讲的另一种方式,这里的详细过程,我们下一节再讲        XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());        xmlParser.parse();      }    }  }

parseCache()方法和parseCacheRef()方法涉及到缓存,我们之后再讲,我们主要来看parseStatement方法:

  void parseStatement(Method method) {    // 若该方法只有一个参数,则返回该参数本身Class对象,如果大于一个参数,则固定返回ParamMap.class    Class<?> parameterTypeClass = getParameterType(method);    // 该方法上是否定义了@Lang注解,否则获取一个默认的LanguageDriver     LanguageDriver languageDriver = getLanguageDriver(method);    // 通过方法上的注解生成一个SqlSource    SqlSource sqlSource = getSqlSourceFromAnnotations(method, parameterTypeClass, languageDriver);    if (sqlSource != null) {      Options options = method.getAnnotation(Options.class);      // 这个mappedStatementId比较重要,就是每个语句的唯一标识      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;      boolean flushCache = !isSelect;      boolean useCache = isSelect;      KeyGenerator keyGenerator;      String keyProperty = "id";      String keyColumn = null;      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();      }      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) {        resultMapId = parseResultMap(method);      }      // 最终调用addMappedStatement方法      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);    }  }

上面的方法看起来比较复杂,主要就是解析各种注解,最终调用addMappedStatement方法,将一个方法封装成一个MappedStatement:

  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);    statementBuilder.resource(resource);    statementBuilder.fetchSize(fetchSize);    statementBuilder.statementType(statementType);    statementBuilder.keyGenerator(keyGenerator);    statementBuilder.keyProperty(keyProperty);    statementBuilder.keyColumn(keyColumn);    statementBuilder.databaseId(databaseId);    statementBuilder.lang(lang);    statementBuilder.resultOrdered(resultOrdered);    statementBuilder.resulSets(resultSets);    setStatementTimeout(timeout, statementBuilder);    setStatementParameterMap(parameterMap, parameterType, statementBuilder);    setStatementResultMap(resultMap, resultType, resultSetType, statementBuilder);    setStatementCache(isSelect, flushCache, useCache, currentCache, statementBuilder);    MappedStatement statement = statementBuilder.build();    // 最终调用该方法,将MappedStatement加入到Configuration中    configuration.addMappedStatement(statement);    return statement;  }  public void addMappedStatement(MappedStatement ms) {    mappedStatements.put(ms.getId(), ms);  }

综上,我们可以看出,当我们使用class类去配置mybatis时,可以使用注解的方法,也可以使用xml文件,但是该xml文件需要和class类的路径相同.最终每条sql或者说每个接口方法都会被解析成一个mappedStatement加入到Configuration中.每个mappedStatement有其唯一的id(在该篇文章中,我们看到其中使用的id是class的类名+方法名).