使用 log4j2 以编程方式创建文件追加程序时出错

Question

在线阅读文档后，我想尝试在本地计算机上测试FileAppender。当我通过调用构建方法创建对象时，出现错误。

我将在应用程序中升级 log4j 版本，当我无法在本地创建和测试文件追加器时，我正在学习文件追加器。我尝试在互联网上查找，并找到了一些有关如何创建它的代码。当我尝试相同的操作时，我在堆栈跟踪中显示以下错误。我正在使用Windows机器并在netbeans上运行代码。

package logtest;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.appender.FileAppender;
class Test
{ 
public void appendLogs(String logEvent)
{
LoggerContext ctx = (LoggerContext)LogManager.getContext(false);
Configuration conf = ctx.getConfiguration();
FileAppender.Builder b = FileAppender.newBuilder();
b.withFileName("TestFile");
b.withAppend(true);
b.build();
FileAppender fa = b.build();
System.out.println(fa.toString());
fa.start();
fa.error("Error message");
}
}
public class LogTest {
private static final Logger LOG = LogManager.getLogger(LogTest.class);
public static void main(String[] args) {
Test t = new Test();
t.appendLogs("Test log");
System.out.println(t.toString());
t.appendLogs("This is an error in a file");
LOG.debug("This Will Be Printed On Debug");
LOG.info("This Will Be Printed On Info");
LOG.warn("This Will Be Printed On Warn");
LOG.error("This Will Be Printed On Error");
LOG.fatal("This Will Be Printed On Fatal");
LOG.info("Appending string: {}.", "Hello, World");
}
}

我在调用 build(( 方法期间收到错误。

Exception in thread "main" java.lang.NullPointerException: name
at java.util.Objects.requireNonNull(Objects.java:228)
at org.apache.logging.log4j.core.appender.AbstractAppender.<init>(AbstractAppender.java:205)
at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.<init>(AbstractOutputStreamAppender.java:120)
at org.apache.logging.log4j.core.appender.FileAppender.<init>(FileAppender.java:259)
at org.apache.logging.log4j.core.appender.FileAppender.<init>(FileAppender.java:42)
at org.apache.logging.log4j.core.appender.FileAppender$Builder.build(FileAppender.java:104)
at logtest.Test.appendLogs(LogTest.java:17)
at logtest.LogTest.main(LogTest.java:31)
Java Result: 1

我不明白为什么我得到空异常。

Answer 1

您需要为追加器设置一个名称。

FileAppender.Builder b = FileAppender.newBuilder();
b.withFileName("TestFile");
b.withAppend(true);
b.setName("my-appender");
b.build();
FileAppender fa = b.build();