setUncaughtExceptionHandler在Maven项目中不起作用

Question

setUncaughtExceptionHandler在Maven项目中不起作用

我正在尝试处理应用程序中主线程上未捕获的异常，因此我可以将它们记录到文件中（我的应用程序是命令行应用程序，可以在通宵工作中运行，因此如果出现问题，我希望管理员能够轻松查看例外）。我已将其简化为一个尽可能简单的测试用例。

生成的Maven应用（根据入门文档）：

   mvn -B archetype:generate \
      -DarchetypeGroupId=org.apache.maven.archetypes \
      -DgroupId=com.mycompany.app \
      -DartifactId=my-app

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App.java：

package com.mycompany.app;

public class App {

    public static void main(String[] args) throws Exception {
        Thread.currentThread().setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            public void uncaughtException(Thread t, Throwable e) {
                System.out.println("Handled exception - let's log it!");
                // Logging code here
            }
        });

        System.out.println("Exception testing");
        throw new Exception("Catch and log me!");
    }

}

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与mvn exec:java产生一起运行：

[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[WARNING] 
[WARNING] Some problems were encountered while building the effective model for com.mycompany.app:my-app:jar:1.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.codehaus.mojo:exec-maven-plugin is missing. @ line 20, column 15
[WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING] 
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building my-app 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- exec-maven-plugin:1.4.0:java (default-cli) @ my-app ---
Exception testing
[WARNING] 
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:293)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.Exception: Catch and log me!
    at com.mycompany.app.App.main(App.java:14)
    ... 6 more
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.493 s
[INFO] Finished at: 2015-10-26T10:57:00+00:00
[INFO] Final Memory: 8M/240M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.4.0:java (default-cli) on project my-app: An exception occured while executing the Java class. null: InvocationTargetException: Catch and log me! -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.4.0:java (default-cli) on project my-app: An exception occured while executing the Java class. null
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:216)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:862)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:286)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:197)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.apache.maven.plugin.MojoExecutionException: An exception occured while executing the Java class. null
    at org.codehaus.mojo.exec.ExecJavaMojo.execute(ExecJavaMojo.java:345)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
    ... 20 more
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:293)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.Exception: Catch and log me!
    at com.mycompany.app.App.main(App.java:14)
    ... 6 more

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与简单的Java应用程序运行相同的代码可以正常工作。App.java：

public class App {

    public static void main(String[] args) throws Exception {
        Thread.currentThread().setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            public void uncaughtException(Thread t, Throwable e) {
                System.out.println("Handled exception - let's log it!");
                // Logging code here
            }
        });

        System.out.println("Exception testing");
        throw new Exception("Catch and log me!");
    }

}

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运行javac App.java && java App产生：

Exception testing
Handled exception - let's log it!

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我怀疑给出的建议是“您不应有任何未捕获的异常”，但是我不确定我是否保证这一点，并且无论如何对Maven和非Maven结果之间的差异感到好奇。

Answer 1

Ren*_*ink 3

不会JavaExecMojo派生新进程。main相反，它在与 mojo 相同的线程中调用该方法。因此它们必须捕获 main 方法抛出的任何异常并模拟 jvm 的行为。

我认为这是 maven exec 插件中的一个错误。看一下ExecJavaMojo的源代码。

唯一JavaExecMojo的用途

Thread.currentThread().getThreadGroup().uncaughtException( Thread.currentThread(), e );

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模拟未捕获的异常行为。但这是不正确的，因为如果当前线程没有注册未捕获的异常处理程序，则 JVM 仅会调用uncaughtException方法。请参阅ThreadGroup.uncaughtException(Thread t, Throwable e)ThreadGroup的 javadoc 。

当该线程组中的线程由于未捕获的异常而停止，并且该线程没有安装特定的 Thread.UncaughtExceptionHandler 时，由 Java 虚拟机调用。

我猜开发者想要做的是

try {
   .... 
   // invoke main method
} catch (Exception e) {
  Thread currentThread = Thread.currentThread();
  Thread.UncaughtExceptionHandler ueh = currentThread.getUncaughtExceptionHandler();
  if (ueh == null) {
    currentThread.getThreadGroup().uncaughtException(currentThread, e);
  } else {
    ueh.uncaughtException(currentThread, e);
  }
}

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这将模拟 JVM 的行为。

您可以使用defaultUncaughtExceptionHandler作为快速修复。

Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
  public void uncaughtException(Thread t, Throwable e) {
    System.out.println("Handled exception - let's log it!");
    // Logging code here
  }
});

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编辑

但是，使用 defaultUncaughtExceptionHandler 会产生相同的 java.lang.reflect.InitationTargetException。

你是对的。他们又做了一个把戏。他们使用自己的ThreadGroup实现。看IsolatedThreadGroup

class IsolatedThreadGroup extends ThreadGroup {
     private Throwable uncaughtException; // synchronize access to this

     public IsolatedThreadGroup( String name ){
        super( name );
     }

    public void uncaughtException( Thread thread, Throwable throwable ) {
        if ( throwable instanceof ThreadDeath ) {
           return; // harmless
        }
        synchronized ( this ) {
            if ( uncaughtException == null ) {
                uncaughtException = throwable; // will be reported eventually
           }
        }
        getLog().warn( throwable );
    }
 }

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javadoc 强制uncaughtException执行这一点

ThreadGroup 的 uncaughtException 方法执行以下操作：

如果该线程组有一个父线程组，则使用相同的两个参数调用该父线程组的 uncaughtException 方法。

否则，此方法检查是否安装了默认的未捕获异常处理程序，如果有，则使用相同的两个参数调用其 uncaughtException 方法。

否则，此方法确定 Throwable 参数是否是 ThreadDeath 的实例。如果是这样，则无需执行任何特殊操作。否则，将使用 Throwable 的 printStackTrace 方法将包含线程名称（从线程的 getName 方法返回）和堆栈回溯的消息打印到标准错误流。

所以他们的实现不符合 api 标准。这就是为什么defaultUncaughtExceptionHandler不起作用。

结论

不要使用JavaExecMojo. 使用ExecMojo代替。例如

 mvn exec:exec -Dexec.executable="java" -Dexec.workingdir="someDir" -Dexec.args="-cp target/classes"

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在 pom 中指定插件属性，您可以使用占位符。例如

<workingdir>${basedir}</workingdir>
<args>-cp ${project.build.outputDirectory}</args>

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