[Java知识库]3.mybatis中的责任链

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目录

概 述

mybatis中的责任链

mybatis 中的责任链使用了注解的方式来识别handler类，内部并没有实现，只是预留出接口。

public interface Interceptor {
 
  Object intercept(Invocation invocation) throws Throwable;
 
  Object plugin(Object target);
 
  void setProperties(Properties properties);
 
}

注解接口如下：

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Intercepts {
  Signature[] value();
}

责任链类：

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

在实例化Executor、ParameterHandler、ResultSetHandler、StatementHandler这4个对象时，把这4个对象植入到责任链中，然后用处理类对这些对象做一些操作：

public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
  }
 
  public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,
      ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return resultSetHandler;
  }
 
  public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
  }
 
  public Executor newExecutor(Transaction transaction) {
    return newExecutor(transaction, defaultExecutorType);
  }
 
  public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    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);
    }
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

总结：

相关工具如下：

分析：

小结：

主要讲述了接下来mybatis中的责任链模式应用，请大家指正~

参考资料和推荐阅读

1.链接: 参考资料.