java MyBatis拦截器Inteceptor详细介绍

      2020-02-14 15:54      JAVA编程
这篇文章主要介绍了java MyBatis拦截器Inteceptor详细介绍的相关资料,需要的朋友可以参考下

有许多java初学者对于MyBatis拦截器Inteceptor不是很了解,在这里我来为各位整理下篇关于java中MyBatis拦截器Inteceptor详解,

本文主要分析MyBatis的插件机制,实际就是Java动态代理实现的责任链模式实现。

根据官方文档。Mybatis只允许拦截以下方法,这个决定写拦截器注解签名参数。

代码如下

Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)ParameterHandler (getParameterObject, setParameters)ResultSetHandler (handleResultSets, handleOutputParameters)StatementHandler (prepare, parameterize, batch, update, query)

拦截处理的源码如下,其中interceptorChain.pluginAll(..)即为织入自定义拦截器:

代码如下

/* org.apache.ibatis.session.Configuration类中方法 */public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {  ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);  /* 拦截ParameterHandler*/  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);  /* 拦截ResultSetHandler*/  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);   /* 拦截StatementHandler*/  statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);  return statementHandler;}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); }  /* 拦截Executor*/ executor = (Executor) interceptorChain.pluginAll(executor); return executor;}

实现一个自定义拦截器只需实现Interceptor接口即可,大致代码如下:

代码如下

/* 注解表明要拦截哪个接口的方法及其参数 */@Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = { Connection.class }) })public class YourInterceptor implements Interceptor{ public Object intercept(Invocation invocation) throws Throwable{  doSomeThing();  /* 注:此处实际上使用Invocation.proceed()方法完成interceptorChain链的遍历调用(即执行所有注册的Interceptor的intercept方法),到最终被代理对象的原始方法调用 */  return invocation.proceed(); }  /*生成成对目标target的代理,而@Intercepts的注解是在Plugin.wrap中用到*/ @Override public Object plugin(Object target){   /* 当目标类是StatementHandler类型时,才包装目标类,不做无意义的代理 */  return (target instanceof StatementHandler)?Plugin.wrap(target, this):target; }  /*用于设置自定义的拦截器配置参数*/ @Override public void setProperties(Properties properties){ }}

其中,拦截调用的代码均在Plugin.wrap中:

代码如下

/* org.apache.ibatis.plugin.Plugin类 */public class Plugin implements InvocationHandler { /* 省略代码... */ public static Object wrap(Object target, Interceptor interceptor) {  /* 此处即为获取Interceptor的注解签名 */  Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);  Class<?> type = target.getClass();  /* 获取拦截目标类相匹配的接口 */  Class<?>[] interfaces = getAllInterfaces(type, signatureMap);  if (interfaces.length > 0) {   /* 使用jdk动态代理 */   return Proxy.newProxyInstance(type.getClassLoader(), interfaces, new Plugin(target, interceptor, signatureMap));  }  return target; } /* 拦截目标类的所有方法的执行都会变为在此执行 */ @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {  try {   Set<Method> methods = signatureMap.get(method.getDeclaringClass());   if (methods != null && methods.contains(method)) {    /* 执行拦截器方法 */    return interceptor.intercept(new Invocation(target, method, args));   }   return method.invoke(target, args);  } catch (Exception e) {   throw ExceptionUtil.unwrapThrowable(e);  } } /* 省略代码... */}

可以看到MyBatis的拦截器设计核心代码还是比较简单的,但是足够灵活。实际使用时注意,不做无意义的代理(Plugin.wrap)。