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