mybaits源码分析--binding模块(五)

一、binding模块

接下来我们看看在org.apache.ibatis.binding包下提供的Binding模块 ,binding其实在执行sqlSession.getMapper(UserMapper.class);获取接口代理的对象时有用到;


mybaits源码分析--binding模块(五)

发现这个包里面提供的工具比较少,就几个,先来分别了解下他们的作用,然后在串联起来。

1.1 MapperRegistry

这显然是一个注册中心,这个注册中是用来保存MapperProxyFactory对象的,所以这个注册器中提供的功能肯定是围绕MapperProxyFactory的添加和获取操作,来看看具体的代码逻辑
成员变量:

 private final Configuration config;
  // 记录 Mapper 接口和 MapperProxyFactory 之间的关系
  private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();

addMapper方法

  public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) { // 检测 type 是否为接口
      if (hasMapper(type)) { // 检测是否已经加装过该接口
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        // !Map<Class<?>, MapperProxyFactory<?>> 存放的是接口类型,和对应的工厂类的关系
        knownMappers.put(type, new MapperProxyFactory<>(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.

        // 注册了接口之后,根据接口,开始解析所有方法上的注解,例如 @Select >>
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

getMapper方法

  /**
   * 获取Mapper接口对应的代理对象
   */
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    // 获取Mapper接口对应的 MapperProxyFactory 对象
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

通过这个方法本质上获取的就是Mapper接口的代理对象。

1.2 MapperProxyFactory

MapperProxyFactory是一个工厂对象,专门负责创建MapperProxy对象。其中核心字段的含义和功能如下:

/**
 * 负责创建 MapperProxy 对象
 * @author Lasse Voss
 */
public class MapperProxyFactory<T> {

  /**
   * MapperProxyFactory 可以创建 mapperInterface 接口的代理对象
   *     创建的代理对象要实现的接口
   */
  private final Class<T> mapperInterface;
  // 缓存
  private final Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap<>();

  public MapperProxyFactory(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  public Class<T> getMapperInterface() {
    return mapperInterface;
  }

  public Map<Method, MapperMethodInvoker> getMethodCache() {
    return methodCache;
  }

  @SuppressWarnings("unchecked")
  /**
   * 创建实现了 mapperInterface 接口的代理对象
   */
  protected T newInstance(MapperProxy<T> mapperProxy) {
    // 1:类加载器:2:被代理类实现的接口、3:实现了 InvocationHandler 的触发管理类
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

}

1.3 MapperProxy

通过MapperProxyFactory创建的MapperProxy是Mapper接口的代理对象,实现了InvocationHandler接口,通过前面讲解的动态代理模式,那么这部分的内容就很简单了。

/**
 * Mapper 代理对象
 * @author  
 * @author  
 */
public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -4724728412955527868L;
  private static final int ALLOWED_MODES = MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED
      | MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC;
  private static final Constructor<Lookup> lookupConstructor;
  private static final Method privateLookupInMethod;
  private final SqlSession sqlSession; // 记录关联的 SqlSession对象
  private final Class<T> mapperInterface; // Mapper接口对应的Class对象
  // 用于缓存MapperMethod对象,key是Mapper接口方法对应的Method对象,value是对应的MapperMethod对象。‘
  // MapperMethod对象会完成参数转换以及SQL语句的执行
  // 注意:MapperMethod中并不会记录任何状态信息,可以在多线程间共享
  private final Map<Method, MapperMethodInvoker> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethodInvoker> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  static {
    Method privateLookupIn;
    try {
      privateLookupIn = MethodHandles.class.getMethod("privateLookupIn", Class.class, MethodHandles.Lookup.class);
    } catch (NoSuchMethodException e) {
      privateLookupIn = null;
    }
    privateLookupInMethod = privateLookupIn;

    Constructor<Lookup> lookup = null;
    if (privateLookupInMethod == null) {
      // JDK 1.8
      try {
        lookup = MethodHandles.Lookup.class.getDeclaredConstructor(Class.class, int.class);
        lookup.setAccessible(true);
      } catch (NoSuchMethodException e) {
        throw new IllegalStateException(
            "There is neither ‘privateLookupIn(Class, Lookup)‘ nor ‘Lookup(Class, int)‘ method in java.lang.invoke.MethodHandles.",
            e);
      } catch (Exception e) {
        lookup = null;
      }
    }
    lookupConstructor = lookup;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      // toString hashCode equals getClass等方法,无需走到执行SQL的流程
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else {
        // 提升获取 mapperMethod 的效率,到 MapperMethodInvoker(内部接口) 的 invoke
        // 普通方法会走到 PlainMethodInvoker(内部类) 的 invoke
        return cachedInvoker(method).invoke(proxy, method, args, sqlSession);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
  }

  private MapperMethodInvoker cachedInvoker(Method method) throws Throwable {
    try {
      // Java8 中 Map 的方法,根据 key 获取值,如果值是 null,则把后面Object 的值赋给 key
      // 如果获取不到,就创建
      // 获取的是 MapperMethodInvoker(接口) 对象,只有一个invoke方法
      // 根据method 去methodCache中获取 如果返回空 则用第二个参数填充
      return methodCache.computeIfAbsent(method, m -> {
        if (m.isDefault()) {
          // 接口的默认方法(Java8),只要实现接口都会继承接口的默认方法,例如 List.sort()
          try {
            if (privateLookupInMethod == null) {
              return new DefaultMethodInvoker(getMethodHandleJava8(method));
            } else {
              return new DefaultMethodInvoker(getMethodHandleJava9(method));
            }
          } catch (IllegalAccessException | InstantiationException | InvocationTargetException
              | NoSuchMethodException e) {
            throw new RuntimeException(e);
          }
        } else {
          // 创建了一个 MapperMethod
          return new PlainMethodInvoker(new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
        }
      });
    } catch (RuntimeException re) {
      Throwable cause = re.getCause();
      throw cause == null ? re : cause;
    }
  }

  private MethodHandle getMethodHandleJava9(Method method)
      throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
    final Class<?> declaringClass = method.getDeclaringClass();
    return ((Lookup) privateLookupInMethod.invoke(null, declaringClass, MethodHandles.lookup())).findSpecial(
        declaringClass, method.getName(), MethodType.methodType(method.getReturnType(), method.getParameterTypes()),
        declaringClass);
  }

  private MethodHandle getMethodHandleJava8(Method method)
      throws IllegalAccessException, InstantiationException, InvocationTargetException {
    final Class<?> declaringClass = method.getDeclaringClass();
    return lookupConstructor.newInstance(declaringClass, ALLOWED_MODES).unreflectSpecial(method, declaringClass);
  }

  interface MapperMethodInvoker {
    Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable;
  }

  private static class PlainMethodInvoker implements MapperMethodInvoker {
    private final MapperMethod mapperMethod;

    public PlainMethodInvoker(MapperMethod mapperMethod) {
      super();
      this.mapperMethod = mapperMethod;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {
      // SQL执行的真正起点
      return mapperMethod.execute(sqlSession, args);
    }
  }

  private static class DefaultMethodInvoker implements MapperMethodInvoker {
    private final MethodHandle methodHandle;

    public DefaultMethodInvoker(MethodHandle methodHandle) {
      super();
      this.methodHandle = methodHandle;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {
      return methodHandle.bindTo(proxy).invokeWithArguments(args);
    }
  }
}

1.4 MapperMethod

MapperMethod中封装了Mapper接口中对应方法的信息,以及SQL语句的信息,可以把MapperMethod看成是配置文件中定义的SQL语句和Mapper接口的桥梁。
mybaits源码分析--binding模块(五)

 

 属性和构造方法

  // statement id (例如:com.gupaoedu.mapper.BlogMapper.selectBlogById) 和 SQL 类型
  private final SqlCommand command;
  // 方法签名,主要是返回值的类型
  private final MethodSignature method;

  public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
    this.command = new SqlCommand(config, mapperInterface, method);
    this.method = new MethodSignature(config, mapperInterface, method);
  }

1.4.1 SqlCommand

SqlCommand是MapperMethod中定义的内部类,记录了SQL语句名称以及对应的类型(UNKNOWN,INSERT,UPDATE,DELETE,SELECT,FLUSH)
mybaits源码分析--binding模块(五)

 

1.4.2 MethodSignature

MethodSignature也是MapperMethod的内部类,在其中封装了Mapper接口中定义的方法相关信息。

  private final boolean returnsMany; // 判断返回是否为 Collection类型或者数组类型
    private final boolean returnsMap; // 返回值是否为 Map类型
    private final boolean returnsVoid; // 返回值类型是否为 void
    private final boolean returnsCursor; // 返回值类型是否为 Cursor 类型
    private final boolean returnsOptional; // 返回值类型是否为 Optional 类型
    private final Class<?> returnType; // 返回值类型
    private final String mapKey; // 如果返回值类型为 Map  则 mapKey 记录了作为 key的 列名
    private final Integer resultHandlerIndex; // 用来标记该方法参数列表中 ResultHandler 类型参数的位置
    private final Integer rowBoundsIndex; // 用来标记该方法参数列表中 rowBounds 类型参数的位置
    private final ParamNameResolver paramNameResolver; // 该方法对应的 ParamNameResolver 对象

构造方法中完成了相关信息分初始化操作

  /**
     * 方法签名
     * @param configuration
     * @param mapperInterface
     * @param method
     */
    public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
      // 获取接口方法的返回类型
      Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
      if (resolvedReturnType instanceof Class<?>) {
        this.returnType = (Class<?>) resolvedReturnType;
      } else if (resolvedReturnType instanceof ParameterizedType) {
        this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
      } else {
        this.returnType = method.getReturnType();
      }
      this.returnsVoid = void.class.equals(this.returnType);
      this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
      this.returnsCursor = Cursor.class.equals(this.returnType);
      this.returnsOptional = Optional.class.equals(this.returnType);
      this.mapKey = getMapKey(method);
      this.returnsMap = this.mapKey != null;
      // getUniqueParamIndex 查找指定类型的参数在 参数列表中的位置
      this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
      this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
      this.paramNameResolver = new ParamNameResolver(configuration, method);
    }

getUniqueParamIndex的主要作用是 查找指定类型的参数在参数列表中的位置

    /**
     * 查找指定类型的参数在参数列表中的位置
     * @param method
     * @param paramType
     * @return
     */
    private Integer getUniqueParamIndex(Method method, Class<?> paramType) {
      Integer index = null;
      // 获取对应方法的参数列表
      final Class<?>[] argTypes = method.getParameterTypes();
      // 遍历
      for (int i = 0; i < argTypes.length; i++) {
        // 判断是否是需要查找的类型
        if (paramType.isAssignableFrom(argTypes[i])) {
          // 记录对应类型在参数列表中的位置
          if (index == null) {
            index = i;
          } else {
            // RowBounds 和 ResultHandler 类型的参数只能有一个,不能重复出现
            throw new BindingException(method.getName() + " cannot have multiple " + paramType.getSimpleName() + " parameters");
          }
        }
      }
      return index;
    }

1.4.3 execute方法

最后来看下再MapperMethod中最核心的方法execute方法,这个方法完成了数据库操作

  public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) { // 根据SQL语句的类型调用SqlSession对应的方法
      case INSERT: {
        // 通过 ParamNameResolver 处理args[] 数组 将用户传入的实参和指定参数名称关联起来
        Object param = method.convertArgsToSqlCommandParam(args);
        // sqlSession.insert(command.getName(), param) 调用SqlSession的insert方法
        // rowCountResult 方法会根据 method 字段中记录的方法的返回值类型对结果进行转换
        result = rowCountResult(sqlSession.insert(command.getName(), param));
        break;
      }
      case UPDATE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
        break;
      }
      case DELETE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
        break;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          // 返回值为空 且 ResultSet通过 ResultHandler处理的方法
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          // 返回值为 单一对象的方法
          Object param = method.convertArgsToSqlCommandParam(args);
          // 普通 select 语句的执行入口 >>
          result = sqlSession.selectOne(command.getName(), param);
          if (method.returnsOptional()
              && (result == null || !method.getReturnType().equals(result.getClass()))) {
            result = Optional.ofNullable(result);
          }
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method ‘" + command.getName()
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

在这个方法中所对应一些分支方法都还是比较简单的,看一下其实就懂,我就不想再往里跟了

1.4.4 核心流程串联

首先在映射文件加载解析的位置,XMLMapperBuilder.parse位置

  public void parse() {
    // 总体上做了两件事情,对于语句的注册和接口的注册
    if (!configuration.isResourceLoaded(resource)) {
      // 1、具体增删改查标签的解析。
      // 一个标签一个MappedStatement。 >>
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      // 2、把namespace(接口类型)和工厂类绑定起来,放到一个map。
      // 一个namespace 一个 MapperProxyFactory >>
      bindMapperForNamespace();
    }

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

在bindMapperForNamespace中会完成Mapper接口的注册并调用前面介绍过的addMapper方法然后就是在我们执行

// 4.通过SqlSession中提供的 API方法来操作数据库
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> list = mapper.selectUserList();

这两行代码的内部逻辑,首先看下getMapper方法

 

 public <T> T getMapper(Class<T> type) {
    return configuration.getMapper(type, this);
  }
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    // mapperRegistry中注册的有Mapper的相关信息 在解析映射文件时 调用过addMapper方法
    return mapperRegistry.getMapper(type, sqlSession);
  }

然后就是从MapperRegistry中获取对应的MapperProxyFactory对象。

  /**
   * 获取Mapper接口对应的代理对象
   */
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    // 获取Mapper接口对应的 MapperProxyFactory 对象
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

然后根据MapperProxyFactory对象获取Mapper接口对应的代理对象。

  /**
   * 创建实现了 mapperInterface 接口的代理对象
   */
  protected T newInstance(MapperProxy<T> mapperProxy) {
    // 1:类加载器:2:被代理类实现的接口、3:实现了 InvocationHandler 的触发管理类
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

不清楚可以看前面画的时序图

mybaits源码分析--binding模块(五)

 

 然后我们再来看下调用代理对象中的方法执行的顺序

List<User> list = mapper.selectUserList();

会进入MapperProxy的Invoker方法中

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      // toString hashCode equals getClass等方法,无需走到执行SQL的流程
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else {
        // 提升获取 mapperMethod 的效率,到 MapperMethodInvoker(内部接口) 的 invoke
        // 普通方法会走到 PlainMethodInvoker(内部类) 的 invoke
        return cachedInvoker(method).invoke(proxy, method, args, sqlSession);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
  }

然后进入PlainMethodInvoker中的invoke方法

    @Override
    public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {
      // SQL执行的真正起点
      return mapperMethod.execute(sqlSession, args);
    }
  }

然后会进入到 MapperMethod的execute方法中

 public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) { // 根据SQL语句的类型调用SqlSession对应的方法
      case INSERT: {
        // 通过 ParamNameResolver 处理args[] 数组 将用户传入的实参和指定参数名称关联起来
        Object param = method.convertArgsToSqlCommandParam(args);
        // sqlSession.insert(command.getName(), param) 调用SqlSession的insert方法
        // rowCountResult 方法会根据 method 字段中记录的方法的返回值类型对结果进行转换
        result = rowCountResult(sqlSession.insert(command.getName(), param));
        break;
      }
      case UPDATE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
        break;
      }
      case DELETE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
        break;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          // 返回值为空 且 ResultSet通过 ResultHandler处理的方法
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          // 返回值为 单一对象的方法
          Object param = method.convertArgsToSqlCommandParam(args);
          // 普通 select 语句的执行入口 >>
          result = sqlSession.selectOne(command.getName(), param);
          if (method.returnsOptional()
              && (result == null || !method.getReturnType().equals(result.getClass()))) {
            result = Optional.ofNullable(result);
          }
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method ‘" + command.getName()
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

之后就会根据对应的SQL类型而调用SqlSession中对应的方法来执行操作

mybaits源码分析--binding模块(五)

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