mybatis之bind模块

2024-01-23 14:44:38

mybatis之bind模块

mybatis通过定义接口mapper,不需要继承或实现接口，Mapper接口中的方法定义select|update|insert|delete方法，通过关联映射文件中定义的sql来执行查询。

 .....org.apache.ibats
 ....................binding
 ...........................BindingException
 ...........................MapperMethod
 ...........................MapperProxy
 ...........................MapperProxyFactory
 ...........................MapperRegistry

执行流程

MybatisUse DefaultSqlSession Configuration MapperRegistry MapperProxyFactory MapperProxy MapperMethod 
public class MybatisUse {

    public static void main(String[] args) throws Exception{
        //加载mybatis的配置文件
        String mybatisXml = "mybatis.xml";
        InputStream inputStream = Resources.getResourceAsStream(mybatisXml);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //获取sqlSession的实现DefaultSqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //通过MapperRegistry获取到Mapper的代理
        CleanPolicyMapper cleanPolicyMapper = sqlSession.getMapper(CleanPolicyMapper.class);
        // 通过MapperMethod执行查询、更新、插入、删除方法逻辑
        CleanPolicy cleanPolicy = cleanPolicyMapper.selectById(292L);
        System.out.println("name:" + cleanPolicy.getName());

        sqlSession.commit();
        sqlSession.flushStatements();
        sqlSession.close();

    }
}

来大体看看调用过程

CleanPolicyMapper cleanPolicyMapper = sqlSession.getMapper(CleanPolicyMapper.class);
//DefaultSqlSession
public class DefaultSqlSession implements SqlSession {
    @Override
    public <T> T getMapper(Class<T> type) {
        return configuration.<T>getMapper(type, this);
    }
}

public class Configuration {
    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        return mapperRegistry.getMapper(type, sqlSession);
    }
}
public class MapperRegistry {
    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        //查询接口对应的代理工厂(有保存对应的接口)
        final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
        if (mapperProxyFactory == null) {
        throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
        }
        try {
        //通过代理工厂实例化代理对象
        return mapperProxyFactory.newInstance(sqlSession);
        } catch (Exception e) {
        throw new BindingException("Error getting mapper instance. Cause: " + e, e);
        }
    }
}

//调用接口对应的方法
CleanPolicy cleanPolicy = cleanPolicyMapper.selectById(292L);
//CleanPolicy ---> 对应这里的MapperProxy对象
public class MapperProxy<T> implements InvocationHanlder, Serializable {

 //代理调用方法
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    //调用执行方法
    return mapperMethod.execute(sqlSession, args);
  }
}

public class MapperMethod {

    //根据执行选择对应的方法
    public Object execute(SqlSession sqlSession, Object[] args) {
        Object result;
        switch (command.getType()) {
        case INSERT: {
    	    Object param = method.convertArgsToSqlCommandParam(args);
            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()) {
            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 {
            Object param = method.convertArgsToSqlCommandParam(args);
            result = sqlSession.selectOne(command.getName(), param);
            }
            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;
  }


}


    classDiagram
        MapperRegistry *-- MapperProxyFactory
        MapperProxyFactory <.. MapperProxy
        MapperProxy *-- MapperMethod
        MapperProxyFactory *-- MapperMethod

MapperRegistry

MapperRegistry映射注册器核心两个方法getMapper和addMapper

public class MapperRegistry {
    private final Configuration config;
    private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();

    // 查询mapper接口的代理对象
    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    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);
    }
  }

 //插入mapper的代理对象，addMapper调用的时机是解析mybatis.xml时
  public <T> void addMapper(Class<T> type) {
      //mapper必须时接口，不能是类
    if (type.isInterface()) {
        //mapper接口必须全局唯一，否则加载时后报错
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      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);
        //在初始化过程中提前发现问题：解析关联mapper接口中方法与映射文件对应的sql，没有则报错，
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

}

MapperProxyFactory

mapper代理工厂，负责实例化代理对象，解耦创建与使用

public class MapperProxyFactory<T> {

 //使用jdk的代理，jdk代理的目标对象必须时接口，这就是mapper必须是接口的原因
  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

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

MapperProxy

MapperProxy使用jdk动态代理

public class MapperProxy<T> implements InvocationHanlder, Serializable {
  // mapper接口  
  private final Class<T> mapperInterface;
  //缓存method方法对应的MapperMethod，加快执行速度
  private final Map<Method, MapperMethod> methodCache;
  
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    //缓存查询是否已有MapperMethod，没有则创建以及加入缓存
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    //执行对应的方法
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

  //缓存查询或创建mapperMethod方法  
 private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
     //缓存没有，则新建mapperMethod方法
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }
}

我们这里关注一下new MapperMethod（）构造函数,看看他都干了那些事儿

public class MapperMethod {

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

   public static class SqlCommand {
    // MapperStatement的id,全局唯一，用来关联映射文件的执行语句 
    private final String name;
    //执行语句的类型select、update、insert、delete
    private final SqlCommandType type;
   }

 //解析出执行方法的返回类型、参数类型 
  public static class MethodSignature {

    private final boolean returnsMany;
    private final boolean returnsMap;
    private final boolean returnsVoid;
    private final boolean returnsCursor;
    private final Class<?> returnType;
    private final String mapKey;
    private final Integer resultHandlerIndex;
    private final Integer rowBoundsIndex;
    private final ParamNameResolver paramNameResolver;

}
    // MapperProxy动态代理调用这里执行真正的方法
  public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    //在MapperMethod的构造器已经存储了执行语句的类型.以及根据返回类型来确定执行哪个操作:selectOne、selectMany......
    switch (command.getType()) {
      case INSERT: {
    	Object param = method.convertArgsToSqlCommandParam(args);
        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()) {
          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 {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
        }
        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;
  }
}

总的来说bind包下的四个类的组合使用，封装了动态sql与mapper接方法的关系以及最终调用执行的胶水代码。

核心: map、jdk动态代理、工厂模式

总结

1.mybatis通过定义接口mapper,不需要继承或实现接口，Mapper接口中的方法定义select|update|insert|delete方法，通过关联映射文件中定义的sql来执行查询。
2.getMapper查询接口对应的代理工厂(有保存对应的接口)
3.MapperRegistry映射注册器核心两个方法getMapper和addMapper
4.插入mapper的代理对象，addMapper调用的时机是解析mybatis.xml时
5.mapper接口必须全局唯一，否则加载时后报错
6.在初始化过程中提前发现问题：解析关联mapper接口中方法与映射文件对应的sql，没有则报错，
7.MapperProxyFactory:mapper代理工厂，负责实例化代理对象，解耦创建与使用
8.使用jdk的代理，jdk代理的目标对象必须时接口，这就是mapper必须是接口的原因
9.缓存method方法对应的MapperMethod,没有则创建以及加入缓存,加快执行速度.
10.MapperStatement的id,全局唯一，用来关联映射文件的执行语句
11.在MapperMethod的构造器已经存储了执行语句的类型.以及根据返回类型来确定执行哪个操作:selectOne、selectMany…

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