自定义Appender ，实现输出log4j日志到GUI

ComponentAppender .java

package log4gui.log4j;

import java.awt.*;
import java.util.Hashtable;
import javax.swing.*;
import javax.swing.text.*;
import org.apache.log4j.*;
import org.apache.log4j.spi.LoggingEvent;

/**
* 扩展AppenderSkeleton，实现append方法即可
*/
public class ComponentAppender extends AppenderSkeleton {

protected Component comp; //用来展现log信息的gui组件
protected int entries;
protected int maxEntries; //记录的最多显示数

public static Appender getAppender(String appenderName) {
return getAppender(appenderName, null);
}

public static Appender getAppender(String appenderName, String categoryName) {
Appender result = null;
Logger testcat;
if (categoryName != null) {
testcat = Logger.getLogger(categoryName);
if (testcat != null) {
result = testcat.getAppender(appenderName);
}
}
if (result == null) {
testcat = Logger.getRootLogger();
result = testcat.getAppender(appenderName);
}
return result;
}

public ComponentAppender() {
this(null);
}

public ComponentAppender(Component comp) {
this(comp, 1);
}

public ComponentAppender(Component comp, int maxEntries) {
MutableAttributeSet attSet;

this.entries = 0;
this.maxEntries = maxEntries;

setComponent(comp);
}

public Component getComponent() {
return this.comp;
}

public void setComponent(Component comp) {
if ((comp instanceof JTextArea) || (comp instanceof JTextPane))
this.layout = new PatternLayout("%n%m");
else
this.layout = new PatternLayout("%m");
this.comp = comp;
}

public int getMaxEntries() {
return this.maxEntries;
}

/**
* Sets the maximum number of logging entries.
*
* @param value - maximum number of logging entries. This value is ignored if the component
* supports just 1 line.
*/
public void setMaxEntries(int value) {
if (this.entries > value) {
// the new maxEntry value is smaller than the actual entry counter
// we have to delete the oldest entries
int toomuch = this.entries - value;

if (comp instanceof JTextPane) {
JTextPane textPane = (JTextPane)comp;
try {
StyledDocument doc = textPane.getStyledDocument();
if (entries == maxEntries) {
Element element = doc.getParagraphElement(0);
int startOfs = element.getStartOffset();
element = doc.getParagraphElement(toomuch - 1);
int endOfs = element.getEndOffset();
doc.remove(startOfs, endOfs - startOfs);
}
} catch (Exception x) {
x.printStackTrace();
}
}
else if (comp instanceof JTextArea) {
JTextArea textArea = (JTextArea)comp;
try {
Document doc = textArea.getDocument();
int endOfs = textArea.getLineEndOffset(toomuch - 1);
int docLen = doc.getLength();
String docText = textArea.getText();
if (docLen < endOfs)
doc.remove(0, docLen);
else
doc.remove(0, endOfs);
textArea.setCaretPosition(doc.getLength());
} catch (Exception x) {
}
}
else if (comp instanceof JComboBox) {
DefaultComboBoxModel model = (DefaultComboBoxModel)((JComboBox)comp).getModel();
for (int i = 0; i < toomuch; i++) {
model.removeElementAt(0);
}
}
else if (comp instanceof java.awt.List) {
for (int i = 0; i < toomuch; i++) {
((java.awt.List)comp).remove(0);
}
}

this.entries = value;
}
this.maxEntries = value;
}

public boolean requiresLayout() {
return true;
}

public void append(LoggingEvent event) {
String text = this.layout.format(event);
// swing components
if (comp instanceof JLabel) {
((JLabel)comp).setText(text);
}
else if (comp instanceof JTextArea) {
JTextArea textArea = (JTextArea)comp;
try {
Document doc = textArea.getDocument();
if (entries == maxEntries) {
// Delete 1 line
int endOfs = textArea.getLineEndOffset(0);
int docLen = doc.getLength();
String docText = textArea.getText();
if (docLen < endOfs)
doc.remove(0, docLen);
else
doc.remove(0, endOfs);
entries -= 1;
}
textArea.append(text);
if (entries == 0)
doc.remove(1, 1);
textArea.setCaretPosition(doc.getLength());
} catch (Exception x) {
};
entries += 1;
}
else if (comp instanceof JTextComponent) {
((JTextComponent)comp).setText(text);
}
else if (comp instanceof JComboBox) {
DefaultComboBoxModel model = (DefaultComboBoxModel)((JComboBox)comp).getModel();
if (entries == maxEntries) {
model.removeElementAt(0);
entries -= 1;
}
model.addElement(text);
entries += 1;
((JComboBox)comp).setSelectedIndex(entries-1);
}
// awt components
else if (comp instanceof java.awt.Label) {
((java.awt.Label)comp).setText(text);
}
else if (comp instanceof java.awt.List) {
if (entries == maxEntries) {
((java.awt.List)comp).remove(0);
entries -= 1;
}
((java.awt.List)comp).add(text);
entries += 1;
}
else if (comp instanceof TextComponent) {
((TextComponent)comp).setText(text);
}
}

/**
* Removes all logging entries from the UI elements
*
*/
public void reset() {
// swing components
if (comp instanceof JLabel) {
((JLabel)comp).setText("");
}
else if (comp instanceof JTextComponent) { // includes JTextArea and JTextPane!
((JTextComponent)comp).setText("");
}
else if (comp instanceof JComboBox) {
DefaultComboBoxModel model = (DefaultComboBoxModel)((JComboBox)comp).getModel();
model.removeAllElements();
}
// awt components
else if (comp instanceof java.awt.Label) {
((java.awt.Label)comp).setText("");
}
else if (comp instanceof java.awt.List) {
((java.awt.List)comp).removeAll();
}
else if (comp instanceof java.awt.TextComponent) {
((java.awt.TextComponent)comp).setText("");
}
this.entries = 0;
}

public void close() {
reset();
}
}

log4j.properties

log4j.rootLogger=DEBUG, stdout, statusline

log4j.log4gui.example.TestLog4j = DEBUG,stdout,statusline
#, logfile, eventlog

# Configure appender stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{dd.MM.yyyy HH:mm:ss} %-5p %-20c - %m%n

# Configure appender statusline
log4j.appender.statusline=log4gui.log4j.ComponentAppender
log4j.appender.statusline.layout=org.apache.log4j.PatternLayout
log4j.appender.statusline.layout.ConversionPattern=%d{dd.MM.yyyy HH:mm:ss} %-5p %-20c - %m
log4j.appender.statusline.Threshold=INFO