Question

我在Aspect中调用bean时遇到了一些错误，我也希望对方面类中bean的初始化有一些建议。

我试图在我的方面类[1]中调用bean [2]，但最后我得到以下错误[4]。似乎@Autowired参数没有初始化bean。我的配置文件在[3]中。我做错了什么？
我希望在初始化期间调用bean一次。因此，即使多次调用map函数，bean也已初始化。另一个解决方案是，我想（我不知道是否可能），当第一次调用切入点map或reduce时，将初始化bean。这些请求可以吗？

谢谢，

[1]我的方面类

@Aspect
@Configurable
@Component
public class MapReduceAspects {
  @Autowired
  MedusaDigests digests;

  @Before("execution(* map(..))")
  public void mymap(JoinPoint joinPoint) {
    System.out.println("My Map Execution: " + joinPoint.getArgs() + ":" + joinPoint.getTarget());
    Object[] obj = joinPoint.getArgs();

    if (obj.length > 0) {
        byte[] key = convertToBytes(obj[0]);
        byte[] value = convertToBytes(obj[1]);

        digests.updateDigest(key, value);
    }
}

@Before("execution(* reduce(..))")
public void myreduce(JoinPoint joinPoint) { System.out.println("My Reduce Execution");
   Object[] obj = joinPoint.getArgs();

   if (obj.length > 0) {
       byte[] key = convertToBytes(obj[0]);
       byte[] value = convertToBytes(obj[1]);

       digests.updateDigest(key, value);
    }
  }
}

[1]我的方面

@Component
public class MedusaDigests {
    private final String MD5 = "MD5";
    private MessageDigest mda = null;

    public MedusaDigests() {
        try {
            mda = MessageDigest.getInstance(MD5);
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
           e.printStackTrace();
       }
    }

    public void updateDigest(byte[] key, byte[] value) {
      mda.update(key);
      mda.update(value);
    }
}

[3]我的beans-aspects.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:aop="http://www.springframework.org/schema/aop"
   xmlns:context="http://www.springframework.org/schema/context"
   xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd">

<aop:aspectj-autoproxy proxy-target-class="true"/>
<!--<aop:include name="mapreduceAspect"/>-->
<!--<aop:include name="jobClient"/>-->
<!--</aop:aspectj-autoproxy>-->
<!--<context:load-time-weaver/>-->
<context:component-scan base-package="org.apache.hadoop.mapred"/>

<bean id="mapreduceAspect" class="org.apache.hadoop.mapred.aspects.MapReduceAspects" factory-method="aspectOf" autowire="byType" />
<bean id="medusaDigests" class="org.apache.hadoop.mapred.MedusaDigests"/>

[4]我得到的错误

WARNING: job_local138234703_0001
java.lang.Exception: java.lang.NullPointerException at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:522)
Caused by: java.lang.NullPointerException
at org.apache.hadoop.mapred.aspects.MapReduceAspects.mymap(MapReduceAspects.java:50)
at org.apache.hadoop.mapred.examples.DummyWordCount$Map.map(DummyWordCount.java:32)
at org.apache.hadoop.mapred.examples.DummyWordCount$Map.map(DummyWordCount.java:1)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:146)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:787)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

Answer 1

首先，您不需要在xml配置中声明bean并使用这样的注释：

<bean id="medusaDigests" class="org.apache.hadoop.mapred.MedusaDigests"/>
@Component
public class MedusaDigests {...}

您必须仅在一个地方声明bean，例如，您可以删除标记：

<bean id="mapreduceAspect" class="org.apache.hadoop.mapred.aspects.MapReduceAspects" factory-method="aspectOf" autowire="byType" />
<bean id="medusaDigests" class="org.apache.hadoop.mapred.MedusaDigests"/>

其次，标记

<context:component-scan base-package="org.apache.hadoop.mapred"/>

不会扫描Autowired注释，如果您还想扫描@Autowired注释，您可以选择以下两种变体之一：

在xml配置中声明

<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>

或

在xml配置中声明

<context:annotation-config/>

在Aspects中自动装配时出错

1 个答案: