利用Arthas排查NoSuchMethodError

1、前言

有时spring boot应用会遇到java.lang.NoSuchMethodError的问题，下面以具体的demo来说明怎样利用arthas来排查。

Demo: https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-NoSuchMethodError

2、在应用的main函数里catch住异常，保证进程不退出

很多时候当应用抛出异常后，进程退出了，就比较难排查问题。可以先改下main函数，把异常catch住：

public static void main(String[] args) throws IOException {try {SpringApplication.run(DemoNoSuchMethodErrorApplication.class, args);} catch (Throwable e) {e.printStackTrace();}// blockSystem.in.read();}

Demo启动之后，抛出的异常是：

java.lang.NoSuchMethodError: org.springframework.core.annotation.AnnotationAwareOrderComparator.sort(Ljava/util/List;)Vat org.springframework.boot.SpringApplication.getSpringFactoriesInstances(SpringApplication.java:394)at org.springframework.boot.SpringApplication.getSpringFactoriesInstances(SpringApplication.java:383)at org.springframework.boot.SpringApplication.initialize(SpringApplication.java:249)at org.springframework.boot.SpringApplication.<init>(SpringApplication.java:225)at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118)at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107)at com.example.demoNoSuchMethodError.DemoNoSuchMethodErrorApplication.main(DemoNoSuchMethodErrorApplication.java:13)

显然，异常的意思是AnnotationAwareOrderComparator缺少sort(Ljava/util/List;)V这个函数。

3、安装arthas

参考：https://alibaba.github.io/arthas/install-detail.html

使用sc命令查找类所在的jar包
应用需要抛出了异常，但是进程还没有退出，我们用arthas来attach上去。比如在mac下面：

./as.sh

然后选择com.example.demoNoSuchMethodError.DemoNoSuchMethodErrorApplication进程。

再执行sc命令来查找类：

$ sc -d org.springframework.core.annotation.AnnotationAwareOrderComparatorclass-info        org.springframework.core.annotation.AnnotationAwareOrderComparatorcode-source       /Users/hengyunabc/.m2/repository/org/springframework/spring/2.5.6.SEC03/spring-2.5.6.SEC03.jarname              org.springframework.core.annotation.AnnotationAwareOrderComparatorisInterface       falseisAnnotation      falseisEnum            falseisAnonymousClass  falseisArray           falseisLocalClass      falseisMemberClass     falseisPrimitive       falseisSynthetic       falsesimple-name       AnnotationAwareOrderComparatormodifier          publicannotationinterfacessuper-class       +-org.springframework.core.OrderComparator+-java.lang.Objectclass-loader      +-sun.misc.Launcher$AppClassLoader@5c647e05+-sun.misc.Launcher$ExtClassLoader@689e3d07classLoaderHash   5c647e05Affect(row-cnt:1) cost in 41 ms.

可以看到AnnotationAwareOrderComparator是从spring-2.5.6.SEC03.jar里加载的。

4、使用jad查看反编绎的源代码

下面使用jad命令来查看AnnotationAwareOrderComparator的源代码

$ jad org.springframework.core.annotation.AnnotationAwareOrderComparatorClassLoader:
+-sun.misc.Launcher$AppClassLoader@5c647e05+-sun.misc.Launcher$ExtClassLoader@689e3d07Location:
/Users/hengyunabc/.m2/repository/org/springframework/spring/2.5.6.SEC03/spring-2.5.6.SEC03.jar/** Decompiled with CFR 0_132.*/
package org.springframework.core.annotation;import java.lang.annotation.Annotation;
import org.springframework.core.OrderComparator;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;public class AnnotationAwareOrderComparator
extends OrderComparator {protected int getOrder(Object obj) {Order order;if (obj instanceof Ordered) {return ((Ordered)obj).getOrder();}if (obj != null && (order = obj.getClass().getAnnotation(Order.class)) != null) {return order.value();}return Integer.MAX_VALUE;}
}Affect(row-cnt:1) cost in 286 ms.