XML轻松学习手册（4）XML快速入门

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 ClassReflex {
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) {
ClassReflex cr = new ClassReflex();
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