雖然log4j2 自帶了很多種Appender 但是有時候避免不了不是自己想要的，這時候我們就需要自定義Appender，使日誌輸出到我們指定的位置，廢話少說，上菜！

package com.hbzx.log;

import java.io.Serializable;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.apache.logging.log4j.core.Filter;
import
 
 org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.appender.AppenderLoggingException;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
import
 
 org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.layout.PatternLayout;

import com.hbzx.frame.MainFrame;

/**
 * 自定義Appender，繼承 AbstractAppender 只需要覆蓋自已想要的方法即可<br>
 * 類上面的註解是用來設定配置檔案中的標籤。
 */
 

@Plugin(name = "TextArea", category = "Core", elementType = "appender", printObject = true)
public class TextAreaAppender extends AbstractAppender {

    /**
     * @fields serialVersionUID
     */
    private static final long serialVersionUID = -830237775522429777L;
    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock readLock = rwLock.readLock();

    //需要實現的構造方法，直接使用父類就行
    protected TextAreaAppender(final String name, final Filter filter, final Layout<? extends Serializable> layout,
            final boolean ignoreExceptions) {
        super(name, filter, layout, ignoreExceptions);
    }

    @Override
    public void append(LogEvent event) {
        readLock.lock();
        try {
            final byte[] bytes = getLayout().toByteArray(event);//日誌二進位制檔案，輸出到指定位置就行
            //下面這個是要實現的自定義邏輯
            MainFrame.log(new String(bytes));
        } catch (Exception ex) {
            if (!ignoreExceptions()) {
                throw new AppenderLoggingException(ex);
            }
        } finally {
            readLock.unlock();
        }
    }

    // 下面這個方法可以接收配置檔案中的引數資訊
    @PluginFactory
    public static TextAreaAppender createAppender(@PluginAttribute("name") String name,
            @PluginElement("Filter") final Filter filter,
            @PluginElement("Layout") Layout<? extends Serializable> layout,
            @PluginAttribute("ignoreExceptions") boolean ignoreExceptions) {
        if (name == null) {
            LOGGER.error("No name provided for MyCustomAppenderImpl");
            return null;
        }
        if (layout == null) {
            layout = PatternLayout.createDefaultLayout();
        }
        return new TextAreaAppender(name, filter, layout, ignoreExceptions);
    }

}

接下來就是配置檔案中的資訊了！

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="info" packages="com.hbzx.log">
    <Properties>
        <Property name="filePath">C:/logs/project.log</Property>
    </Properties>

    <Appenders>
        <!--這個輸出控制檯的配置 -->
        <Console name="console" target="SYSTEM_OUT">
            <!--控制檯只輸出level及以上級別的資訊（onMatch），其他的直接拒絕（onMismatch） -->
            <ThresholdFilter level="DEBUG" onMatch="ACCEPT" onMismatch="DENY" />
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] [%-5p]  %c {%F:%L} - %m%n" />
        </Console>

        <File  name="logFile" fileName="${filePath}">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] [%-5p]  %c {%F:%L} - %m%n" />
        </File>
        
        <!-- 這個就是自定義的Appender -->
        <TextArea name="textarea">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] [%-5p] {%F:%L} - %m%n" />
        </TextArea>
    </Appenders>
    <Loggers>
        <logger name="com.hbzx" level="debug" />
        <logger name="org.apache.http" level="info" />
        <logger name="org.apache.commons" level="info" />
        <logger name="io.netty" level="info" />
        <logger name="org.asynchttpclient" level="info" />

        <Root level="debug">
            <AppenderRef ref="console" />
            <AppenderRef ref="logFile" />
            <AppenderRef ref="textarea" />
        </Root>
    </Loggers>
</Configuration>

雖然log4j2自帶了很多種Appender，但是有時候需要自定義Appender來滿足業務需求。例如log4j2就沒有為Scribe新增appender。
       Appender的自定義其實很簡單，可以參考log4j-core原始碼中org.apache.logging.log4j.core.appender.mom包中其它的擴充套件appender的實現。主要是實現AbstractAppender和AbstractManager。

       編碼完後，在log4j2.xml中新增自定義的appender後執行會發現：

1. 2016-08-0222:46:30,693 main ERROR Error processing element XXX ([Appenders: null]): CLASS_NOT_FOUND  

1. <Configuration status="info" packages="com.zero.scribe.log4j2plugin">