log4j分析

LOG4J是一个非常优秀的开源日志组件，今天对它的源代码进行的一点学习，收获如下：

 

1、调用方法：

   // 初始化一个日志对象
   private static Logger log = Logger.getLogger(MyLog. class);
   // 调用该对象进行日志记录
  log.debug( "good job");

 

2、设置系统属性的方法：

     // JAVA 中设置系统属性的方法
     // 1:
    System.setProperty( "log.key1", "true");
    System.out.println(System.getProperty( "log.key1"));
     // 2:在虚拟机运行参数中添加 -log.key2=goodjobkey
    System.out.println(System.getProperty( "log.key2"));

 

 

3、内部日志类（记录组件内部的日志信息）：

package logtest;

import java.io.IOException;

public class InnerLog {
   public static final String DEBUG_KEY = "mylog.debug";
   private static final String DEBUG_PREFIX = "mylog:DEBUG ";
   private static final String ERR_PREFIX = "mylog:ERROR ";

   protected static boolean debugEnabled = false;
   protected static boolean quietMode = false;

   static {
    String key = System.getProperty(DEBUG_KEY);
    debugEnabled = "true".equalsIgnoreCase(key);
  }

   public static void setDebugEnabled( boolean debugEnabled) {
    InnerLog.debugEnabled = debugEnabled;
  }

   public static void setQuietMode( boolean quietMode) {
    InnerLog.quietMode = quietMode;
  }

   public static void debug(String msg) {
     if (debugEnabled && !quietMode) {
      System.out.println(DEBUG_PREFIX + msg);
    }
  }

   public static void debug(String msg, Throwable t) {
     if (debugEnabled && !quietMode) {
      System.out.println(DEBUG_PREFIX + msg);
       if (t != null) {
        t.printStackTrace(System.out);
      }
    }
  }

   public static void error(String msg) {
     if (!quietMode) {
      System.err.println(ERR_PREFIX + msg);
    }
  }

   public static void error(String msg, Throwable t) {
     if (!quietMode) {
      System.err.println(msg);
       if (t != null) {
        t.printStackTrace(System.err);
      }
    }
  }

   public static void main(String[] args) {
     // 内部日志类
    Throwable t = new IOException( "IOException");
    System.out.println(System.getProperty(InnerLog.DEBUG_KEY));
    InnerLog.debug( "debug inner", t);
    InnerLog.error( "error msg", t);
    InnerLog.setDebugEnabled( true);
     // 输出DEBUG信息
    InnerLog.debug( "debug inner2", t);
    InnerLog.error( "error msg2", t);
    InnerLog.setQuietMode( true);
     // 什么都不输出（安静模式下）
    InnerLog.debug( "debug inner3", t);
    InnerLog.error( "error msg3", t);
  }
}

 

设置了虚拟机参数（-Dmylog.debug=true）的输出：

true
mylog:DEBUG debug inner
java.io.IOException: IOException
  at logtest.MyLog.main(MyLog.java:21)
mylog:DEBUG debug inner2
java.io.IOException: IOException
  at logtest.MyLog.main(MyLog.java:21)
error msg
java.io.IOException: IOException
  at logtest.MyLog.main(MyLog.java:21)
error msg2
java.io.IOException: IOException
  at logtest.MyLog.main(MyLog.java:21)

没有设置mylog.debug参数的输出：

null
mylog:DEBUG debug inner2
java.io.IOException: IOException
  at logtest.MyLog.main(MyLog.java:21)
error msg
java.io.IOException: IOException
  at logtest.MyLog.main(MyLog.java:21)
error msg2
java.io.IOException: IOException

 

4-、加载properties文件及解析${}型参数：

package logtest;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class PropConfig {
   private static final String CFG_FILE = "mylog.properties";
   protected static Properties props;
   static String DELIM_START = "${";
   static char DELIM_STOP = '}';
   static int DELIM_START_LEN = 2;
   static int DELIM_STOP_LEN = 1;

   static {
    props = new Properties();
    InputStream input = null;
     try {
      String fileName = PropConfig. class.getClassLoader().getResource(CFG_FILE).getFile();
      input = new FileInputStream( new File(fileName));
      props.load(input);
      input.close();
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
       if (input != null) {
         try {
          input.close();
        } catch (IOException e) {
        }
      }
    }
     // props.list(System.out);
  }

   public static String substVal(String str) {
     if (str == null) {
       return "";
    }
    StringBuffer sbuf = new StringBuffer(128);
     int i = 0;
     int j = 0;
     int k = 0;
     while ( true) {
      j = str.indexOf(DELIM_START, i);
       if (j == -1) {
         if (i == 0) {
           return str;
        } else {
           return sbuf.append(str.substring(i, str.length())).toString();
        }
      } else {
        sbuf.append(str.substring(i, j));
        k = str.indexOf(DELIM_STOP, j);
         if (k == -1) {
           throw new IllegalArgumentException( "有开始符号没有结束符号！");
        } else {
          j += DELIM_START_LEN;
          String key = str.substring(j, k);
          String replaceStr = props.getProperty(key);
           // 如果没有替换项，则保持空
           if (replaceStr != null) {
            sbuf.append(substVal(replaceStr));
          }
          i = k + DELIM_STOP_LEN;
        }

      }
    }
  }

   public static void main(String[] args) {
    String str = "good job ${username},${datetime}!";
    props.setProperty( "username", "kink");
    props.setProperty( "datetime", "2009-4-14 ${time}");
    props.setProperty( "time", "15:07");
    System.out.println(substVal(str));
  }
}

输出结果如下：

good job kink,2009-4-14 15:07!

 

5、利用反射机制创建对象并实现属性的赋值：

首先创建一个简单的VO对象：

package logtest;

public class User {
   private String name;
   private long id;
   private int age;
   private boolean bool;

   public String getName() {
     return name;
  }

   public void setName(String name) {
     this.name = name;
  }

   public long getId() {
     return id;
  }

   public void setId( long id) {
     this.id = id;
  }

   public int getAge() {
     return age;
  }

   public void setAge( int age) {
     this.age = age;
  }

   public boolean isBool() {
     return bool;
  }

   public void setBool( boolean bool) {
     this.bool = bool;
  }

   public String toString() {
     return "name:" + name + " id:" + id + " age:" + age + " bool:" + bool;
  }
}

 

实现对上面User类的创建及属性的赋值：

package logtest;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.util.Enumeration;
import java.util.Properties;

public class Cla***eflex {
   public Object getObject(String className, Properties props) throws Exception {
     // 获得类对象
    Class clazz = Class.forName(className);
     // 取得BEAN信息
    BeanInfo bi = Introspector.getBeanInfo(clazz);
     // 获取属性描述
    PropertyDescriptor[] descs = bi.getPropertyDescriptors();
    Object obj = clazz.newInstance();
     for (Enumeration e = props.propertyNames(); e.hasMoreElements();) {
      String key = (String) e.nextElement();
      String value = props.getProperty(key);
       if (value != null) {
        key = Introspector.decapitalize(key);
        PropertyDescriptor desc = this.getPropertyDescriptor(key, descs);
         this.setProperty(obj, desc, key, value);
      }
    }
     return obj;
  }

   private PropertyDescriptor getPropertyDescriptor(String name, PropertyDescriptor[] descs) {
     for ( int i = 0; i < descs.length; i++) {
       if (name.equals(descs[i].getName())) {
         return descs[i];
      }
    }
     return null;
  }

   private void setProperty(Object obj, PropertyDescriptor desc, String name, String value) {
    Method setter = desc.getWriteMethod();
    Class[] paramTypes = setter.getParameterTypes();
    Object arg = this.convertArg(value, paramTypes[0]);
     try {
      setter.invoke(obj, new Object[] { arg });
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

   protected Object convertArg(String val, Class type) {
     if (val == null)
       return null;
    String v = val.trim();
     if (String. class.isAssignableFrom(type)) {
       return val;
    } else if (Integer.TYPE.isAssignableFrom(type)) {
       return new Integer(v);
    } else if (Long.TYPE.isAssignableFrom(type)) {
       return new Long(v);
    } else if (Boolean.TYPE.isAssignableFrom(type)) {
       if ( "true".equalsIgnoreCase(v)) {
         return Boolean.TRUE;
      } else if ( "false".equalsIgnoreCase(v)) {
         return Boolean.FALSE;
      }
    }
     return null;
  }

   public static void main(String[] args) {
    Cla***eflex cr = new Cla***eflex();
    Properties props = new Properties();
    props.setProperty( "name", "kink");
    props.setProperty( "Id", "20009");
    props.setProperty( "age", "23");
    props.setProperty( "bool", "true");

    User user = null;
     try {
      user = (User) cr.getObject(User. class.getName(), props);
    } catch (Exception e) {
      e.printStackTrace();
    }
    System.out.println(user);
  }
}

输出结果如下：

name:kink id:20009 age:23 bool:true