【发布时间】：2014-08-25 15:14:50
【问题描述】：
我对 Log4j2 很陌生，所以可能不是错误，只是我不知道如何正确使用它。
我想通过 log4j.configurationFile 系统属性指定的配置文件来配置 Log4j2。 在我之前的实验中，我能够使用正确放置的 log4j2.xml 配置 log4j2，并且工作正常。 现在如果系统属性存在，我得到 NullPointerException：
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T E S T S
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Running newpackage.Log4jSyspropProblemTest
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
Caused by: java.lang.NullPointerException
at java.io.Writer.write(Writer.java:157)
at java.io.BufferedWriter.newLine(BufferedWriter.java:243)
at java.io.PrintStream.newLine(PrintStream.java:544)
at java.io.PrintStream.println(PrintStream.java:824)
at java.lang.Throwable$WrappedPrintStream.println(Throwable.java:748)
at java.lang.Throwable.printStackTrace(Throwable.java:655)
at java.lang.Throwable.printStackTrace(Throwable.java:643)
at org.apache.logging.log4j.simple.SimpleLogger.logMessage(SimpleLogger.java:165)
at org.apache.logging.log4j.status.StatusLogger.logMessage(StatusLogger.java:220)
at org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:1336)
at org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:1325)
at org.apache.logging.log4j.spi.AbstractLogger.error(AbstractLogger.java:551)
at org.apache.logging.log4j.core.pattern.PatternParser.createConverter(PatternParser.java:528)
at org.apache.logging.log4j.core.pattern.PatternParser.finalizeConverter(PatternParser.java:569)
at org.apache.logging.log4j.core.pattern.PatternParser.parse(PatternParser.java:364)
at org.apache.logging.log4j.core.pattern.PatternParser.parse(PatternParser.java:163)
at org.apache.logging.log4j.core.layout.PatternLayout.<init>(PatternLayout.java:124)
at org.apache.logging.log4j.core.layout.PatternLayout.<init>(PatternLayout.java:54)
at org.apache.logging.log4j.core.layout.PatternLayout$Builder.build(PatternLayout.java:368)
at org.apache.logging.log4j.core.config.DefaultConfiguration.<init>(DefaultConfiguration.java:56)
at org.apache.logging.log4j.core.LoggerContext.<init>(LoggerContext.java:72)
at org.apache.logging.log4j.core.selector.ClassLoaderContextSelector.locateContext(ClassLoaderContextSelector.java:218)
at org.apache.logging.log4j.core.selector.ClassLoaderContextSelector.getContext(ClassLoaderContextSelector.java:144)
at org.apache.logging.log4j.core.selector.ClassLoaderContextSelector.getContext(ClassLoaderContextSelector.java:80)
at org.apache.logging.log4j.core.impl.Log4jContextFactory.getContext(Log4jContextFactory.java:72)
at org.apache.logging.log4j.core.impl.Log4jContextFactory.getContext(Log4jContextFactory.java:37)
at org.apache.logging.log4j.LogManager.getLogger(LogManager.java:468)
at newpackage.Log4jSyspropProblemTest.testLoggerSuccesfullyLoaded(Log4jSyspropProblemTest.java:44)
... 30 more
我不知道。在我看来一切都很好。 这是我的属性文件“src/main/resources/AppProperties.properties”：
log4j.configurationFile=src/main/resources/log4j2_custom.xml
src/main/resources/log4j2_custom.xml的相关部分：
<configuration status="info" monitorIntervall="30" strict="true">
<properties>
<Property name="filename">logs/myLog.log</Property>
</properties>
<appenders>
<appender type="File" name="fileAppender" filename="${filename}">
<layout type="PatternLayout">
<pattern>%d %p %C{1.} [%t] %m%n</pattern>
</layout>
</appender>
</appenders>
<loggers>
<logger name="fileLogger">
<appenderRef ref="fileAppender"/>
</logger>
</loggers>
</configuration>
测试：
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class Log4jSyspropProblemTest {
private Logger fileLogger;
private static final String PROPERTIES_FILE = "src/main/resources/AppProperties.properties";
private static final String LOG4J_CONFIGURATION_PROPERTY_NAME = "log4j.configurationFile";
@Test
public void testPropertyIsValid(){
final String configFile = System.getProperty(LOG4J_CONFIGURATION_PROPERTY_NAME);
Assert.assertNotNull(configFile);
Assert.assertTrue(new File(configFile).exists());
}
@Test
public void testLoggerSuccesfullyLoaded(){
fileLogger = LogManager.getLogger("fileLogger");
Assert.assertNotNull(fileLogger);
}
}
最后是来自 pom.xml 的依赖项：
<dependencies>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.0.1</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.0.1</version>
</dependency>
</dependencies>
如果您发现了什么，请告诉我。非常感谢任何想法。
【问题讨论】：
-
我无法想象有人会想要通读所有这些内容 - 您能否将其缩减为最少的信息集，或者使用一些突出显示来指出您的具体问题在哪里？ （除了代码我找不到问号）。
-
感谢您的回答。你问的很难，因为我不知道我在哪里犯了错误。我的具体问题是为什么我得到 NullPointerException，所以最相关的信息是第一个代码，堆栈跟踪。不管怎样，我会尽量删帖。
-
问题似乎已经解决，所以这与问题无关，但如果在模式中使用 %c（小写）而不是 %C，您将获得更好的性能。另外 monitorIntervall="30" 应该是
monitorInterval（末尾有一个“l”）。
标签： nullpointerexception log4j2 system-properties