mybatis源码解析八之other

比眉伴天荒 2023-03-13 11:35 24阅读 0赞

### 文章目录 ###

*  拦截器
 *   *  Configuration
     *  InterceptorChain
     *  Plugin

# 拦截器 #

public interface Interceptor {
        
    //执行拦截逻辑的方法
      Object intercept(Invocation invocation) throws Throwable;
    //决定是否触发intercept （）方法
      default Object plugin(Object target) {
        
        return Plugin.wrap(target, this);
      }
    //根据配置初始化Interceptor 对象
      default void setProperties(Properties properties) {
        
        // NOP
      }
    
    }

## Configuration ##

public class Configuration {
        
    
      public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
        
        executorType = executorType == null ? defaultExecutorType : executorType;
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Executor executor;
       //根据参数，选择合适的Executor 实现
        if (ExecutorType.BATCH == executorType) {
        
          executor = new BatchExecutor(this, transaction);
        } else if (ExecutorType.REUSE == executorType) {
        
          executor = new ReuseExecutor(this, transaction);
        } else {
        
          executor = new SimpleExecutor(this, transaction);
        }
       //根据配置决定是否开启二级缓存的功能
        if (cacheEnabled) {
        
          executor = new CachingExecutor(executor);
        }
       //创建Executor的代理对象
        executor = (Executor) interceptorChain.pluginAll(executor);
        return executor;
      }
      }

## InterceptorChain ##

public class InterceptorChain {
        
    
      private final List<Interceptor> interceptors = new ArrayList<>();
    
      public Object pluginAll(Object target) {
        
      //遍历interceptors 集合
        for (Interceptor interceptor : interceptors) {
        
         //调用
          target = interceptor.plugin(target);
        }
        return target;
      }
    
      public void addInterceptor(Interceptor interceptor) {
        
        interceptors.add(interceptor);
      }
    
      public List<Interceptor> getInterceptors() {
        
        return Collections.unmodifiableList(interceptors);
      }
    
    }

## Plugin ##

public class Plugin implements InvocationHandler {
        
      //目标对象
      private final Object target;
      //Interceptor 对象
      private final Interceptor interceptor;
      //记录了＠ Signature j主解中的信息
      private final Map<Class<?>, Set<Method>> signatureMap;
    
      private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) {
        
        this.target = target;
        this.interceptor = interceptor;
        this.signatureMap = signatureMap;
      }
    
      public static Object wrap(Object target, Interceptor interceptor) {
        
      //负责处理@Signature注解
        Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
      //获取目标类型
        Class<?> type = target.getClass();
      //获取目标类型实现的接口
        Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
        if (interfaces.length > 0) {
        
        //使用JDK 动态代理的方式创建代理对象
          return Proxy.newProxyInstance(
              type.getClassLoader(),
              interfaces,
              new Plugin(target, interceptor, signatureMap));
        }
        return target;
      }
    
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        
        try {
        
          //获取当前方法所在类或接口中，可被当前Interceptor 拦截的方法
          Set<Method> methods = signatureMap.get(method.getDeclaringClass());
          //如果当前调用的方法需妥被拦截，则调用interceptor.intercept()方法进行拦截处理
          if (methods != null && methods.contains(method)) {
        
            return interceptor.intercept(new Invocation(target, method, args));
          }
          //如果当前调用的方法不能被拦截， 9J1J 调用target 对象的相应方法
          return method.invoke(target, args);
        } catch (Exception e) {
        
          throw ExceptionUtil.unwrapThrowable(e);
        }
      }
      }