mybatis之bind模块

小灰灰 2022-09-02 11:51 165阅读 0赞

# 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…