如何在 log4j2 中创建自定义 Appender? [英] How to Create a Custom Appender in log4j2?

问题描述

在此链接中讨论:如何在log4j?

为了在 log4j 1.x 中创建自定义 appender，我们必须扩展 AppenderSkeleton 类并实现其 append 方法.

For creating a custom appender in log4j 1.x we have to extend the AppenderSkeleton class and implements its append method.

同样，我们如何在 log4j2 中创建自定义 appender，因为我们没有要扩展的 AppenderSkelton 类，而所有其他 appender 都扩展了 AppenderBase 类.

Similarly How we can create a custom appender in log4j2 as we dont have AppenderSkelton class to extend and all other appender extend AppenderBase class .

推荐答案

这在 log4j2 中与在 log4j-1.2 中的工作方式完全不同.

This works quite differently in log4j2 than in log4j-1.2.

在 log4j2 中，您将为此创建一个插件.该手册对自定义附加程序的示例进行了说明:http://logging.apache.org/log4j/2.x/manual/extending.html#Appenders

In log4j2, you would create a plugin for this. The manual has an explanation with an example for a custom appender here: http://logging.apache.org/log4j/2.x/manual/extending.html#Appenders

扩展 org.apache.logging.log4j.core.appender.AbstractAppender 可能很方便，但这不是必需的.

It may be convenient to extend org.apache.logging.log4j.core.appender.AbstractAppender, but this is not required.

当您使用 @Plugin(name="MyCustomAppender", .... 注释自定义 Appender 类时，插件名称将成为配置元素名称，因此带有自定义 appender 的配置将看起来像这样:

When you annotate your custom Appender class with @Plugin(name="MyCustomAppender", ...., the plugin name becomes the configuration element name, so a configuration with your custom appender would then look like this:

<Configuration packages="com.yourcompany.yourcustomappenderpackage">
  <Appenders>
    <MyCustomAppender name="ABC" otherAttribute="...">
    ...
  </Appenders>
  <Loggers><Root><AppenderRef ref="ABC" /></Root></Loggers>
</Configuration>

请注意，配置中的 packages 属性是以逗号分隔的所有带有自定义 log4j2 插件的包的列表.Log4j2 将在类路径中搜索这些包中使用@Plugin 注释的类.

Note that the packages attribute on the configuration is a comma-separated list of all the packages with custom log4j2 plugins. Log4j2 will search these packages in the classpath for classes annotated with @Plugin.

这是打印到控制台的示例自定义 appender:

Here is a sample custom appender that prints to the console:

package com.yourcompany.yourcustomappenderpackage;

import java.io.Serializable;
import java.util.concurrent.locks.*;
import org.apache.logging.log4j.core.*;
import org.apache.logging.log4j.core.config.plugins.*;
import org.apache.logging.log4j.core.layout.PatternLayout;

// note: class name need not match the @Plugin name.
@Plugin(name="MyCustomAppender", category="Core", elementType="appender", printObject=true)
public final class MyCustomAppenderImpl extends AbstractAppender {

    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock readLock = rwLock.readLock();

    protected MyCustomAppenderImpl(String name, Filter filter,
            Layout<? extends Serializable> layout, final boolean ignoreExceptions) {
        super(name, filter, layout, ignoreExceptions);
    }

    // The append method is where the appender does the work.
    // Given a log event, you are free to do with it what you want.
    // This example demonstrates:
    // 1. Concurrency: this method may be called by multiple threads concurrently
    // 2. How to use layouts
    // 3. Error handling
    @Override
    public void append(LogEvent event) {
        readLock.lock();
        try {
            final byte[] bytes = getLayout().toByteArray(event);
            System.out.write(bytes);
        } catch (Exception ex) {
            if (!ignoreExceptions()) {
                throw new AppenderLoggingException(ex);
            }
        } finally {
            readLock.unlock();
        }
    }

    // Your custom appender needs to declare a factory method
    // annotated with `@PluginFactory`. Log4j will parse the configuration
    // and call this factory method to construct an appender instance with
    // the configured attributes.
    @PluginFactory
    public static MyCustomAppenderImpl createAppender(
            @PluginAttribute("name") String name,
            @PluginElement("Layout") Layout<? extends Serializable> layout,
            @PluginElement("Filter") final Filter filter,
            @PluginAttribute("otherAttribute") String otherAttribute) {
        if (name == null) {
            LOGGER.error("No name provided for MyCustomAppenderImpl");
            return null;
        }
        if (layout == null) {
            layout = PatternLayout.createDefaultLayout();
        }
        return new MyCustomAppenderImpl(name, filter, layout, true);
    }
}

有关插件的更多详细信息:http://logging.apache.org/log4j/2.x/manual/plugins.html

For more details on plugins: http://logging.apache.org/log4j/2.x/manual/plugins.html

如果手册不够，查看 log4j-core 中内置 appender 的源代码可能会有用.

If the manual is not enough, it may be useful to look at the source code for the built-in appenders in log4j-core.

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