Log4j2 控制台附加程序出现 NullpointerException

问题描述 投票：0回答：4

我的应用程序日志记录在测试中的 Maven 构建期间崩溃。这是我在 src/test/resources 中的 log4j2.xml：

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="INFO">
    <Appenders>
        <Console name="stdout" target="SYSTEM_OUT">
            <PatternLayout pattern="MyApp: %d{yyyy-MM-dd HH:mm:ss,SSS} %5p [%t] %c{1.} - %m%n" />
        </Console>
    </Appenders>

    <Loggers>
        <Logger name="com.my.app" level="info" additivity="false">
            <Appender-ref ref="stdout"/>
        </Logger>
        <Root level="error">
            <Appender-ref ref="stdout"/>
        </Root>
    </Loggers>
</Configuration>

我在构建过程中的测试过程中遇到了这个异常：

2017-11-23 15:12:28,371 main ERROR An exception occurred processing Appender stdout java.lang.NullPointerException
    at org.apache.logging.log4j.core.impl.ThrowableProxy.toExtendedStackTrace(ThrowableProxy.java:671)
    at org.apache.logging.log4j.core.impl.ThrowableProxy.<init>(ThrowableProxy.java:138)
    at org.apache.logging.log4j.core.impl.ThrowableProxy.<init>(ThrowableProxy.java:122)
    at org.apache.logging.log4j.core.impl.Log4jLogEvent.getThrownProxy(Log4jLogEvent.java:566)
    at org.apache.logging.log4j.core.pattern.ExtendedThrowablePatternConverter.format(ExtendedThrowablePatternConverter.java:64)
    at org.apache.logging.log4j.core.pattern.PatternFormatter.format(PatternFormatter.java:38)
    at org.apache.logging.log4j.core.layout.PatternLayout$PatternSerializer.toSerializable(PatternLayout.java:333)
    at org.apache.logging.log4j.core.layout.PatternLayout.toText(PatternLayout.java:232)
    at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:217)
    at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:57)
    at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.directEncodeEvent(AbstractOutputStreamAppender.java:177)
    at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.tryAppend(AbstractOutputStreamAppender.java:170)
    at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:161)
    at org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:156)
    at org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:129)
    at org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:120)
    at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84)
    at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:448)
    at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:433)
    at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:417)
    at org.apache.logging.log4j.core.config.LoggerConfig.logParent(LoggerConfig.java:439)
    at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:434)
    at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:417)
    at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:403)
    at org.apache.logging.log4j.core.config.AwaitCompletionReliabilityStrategy.log(AwaitCompletionReliabilityStrategy.java:63)
    at org.apache.logging.log4j.core.Logger.logMessage(Logger.java:146)
    at org.apache.logging.log4j.spi.AbstractLogger.tryLogMessage(AbstractLogger.java:2116)
    at org.apache.logging.log4j.spi.AbstractLogger.logMessageSafely(AbstractLogger.java:2100)
    at org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:1994)
    at org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:1966)
    at org.apache.logging.slf4j.Log4jLogger.error(Log4jLogger.java:319)
    at com.my.app.MyTest.testingMyApp(MyTest.java:89)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.ExpectException.evaluate(ExpectException.java:19)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
    at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:283)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeWithRerun(JUnit4Provider.java:173)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:153)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:128)
    at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:203)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:155)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103)

这是我的pom：

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-web</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-slf4j-impl</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-jul</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-jcl</artifactId>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
</dependency>
<dependency>
    <groupId>org.dblock.log4jna</groupId>
    <artifactId>log4jna-api</artifactId>
</dependency>

log4j的版本是2.9.1

有趣的是，它会记录到控制台，例如当 Spring 应用程序启动时，我可以看到来自具有 @SpringBootApplication 注释的 MyApplication.java 的日志。

MyTest.java:89 是：

logger.error("error occured",e);

记录器来自：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

所以看起来它在错误日志期间崩溃了，但是如果我记录正常信息就没有问题。

那么这个空指针是什么？

java maven log4j2 appender consoleappender
4个回答
8
投票

好吧，我明白了：这是因为在测试类中我有一个模拟异常。如果我将其更改为从异常中创建一个新对象，它就可以正常工作。

我想它是报告错误的一个很好的候选者。

4
投票

您作为 

Exception
的参数传递的 
Throwable
或 
logger.error("error occured", e);
没有任何堆栈跟踪（其堆栈跟踪是 
null
），但是您正在使用的 Log4j2 实现尝试访问所述堆栈跟踪并抛出此错误。

查看源代码，抛出错误的行是：

stackLength = stackTrace.length;

意味着 

stackTrace
变量是 
null
。它是通过 
throwable.getStackTrace()
 从您作为参数传递给 
 的
Throwable
 (
Exception

) 获得的 
logger.error("error occured", e);

至于为什么你的堆栈跟踪为空，这取决于你正在使用的JVM以及你如何得到所述异常。它可能会发生，但这绝对不是标准行为。你可以看看这个帖子和这个帖子。

0
投票

如果您需要使用Mockito创建模拟异常，则可以设置

getStackTrace
方法以返回
StackTraceElement
的空数组：

private Throwable logSafeExceptionMock(Class<? extends Throwable> exceptionType) {
  Throwable t = mock(exceptionType);
  when(t.getStackTrace()).thenReturn(new StackTraceElement[0]);
  return t;
}
-1
投票

谢谢 Dmitry Timofeev，你拯救了我的一天！

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