tomcat6类加载器与类加载顺序 Author:dyyx007 东阳游侠 http://hi.baidu.com/ajf8/home http://weibo.com/dyyx007 tomcat6.0.32 com.dyyx.ShareUtils //返回系统当前时间 public static String now(); package com.dyyx; import java.text.DateFormat; import java.text.SimpleDateFormat; import java.util.Date; public class ShareUtils { private static final String FULL_DATE_FORMAT = "yyyy-MM-dd HH:mm:ss"; public static String now() { Date now = new Date(); DateFormat dateFormat = new SimpleDateFormat(FULL_DATE_FORMAT); return dateFormat.format(now); } } http://127.0.0.1:8080/tools/share_utils_now.jsp share_utils_now.jsp 里调用 ShareUtils.now() 输出当前时间 并且会调用getClassLoadInfo(Class c) 方法 输出 ShareUtils.class 的类加载器信息 代码如下 public static String getClassLoadInfo(Class c) { String rname = getResourceName(c); URL url = null; ClassLoader cl = c.getClassLoader(); // 如果ClassLoader为NULL 为系统类 if (null == cl) { url = ClassLoader.getSystemResource(rname); } else { url = cl.getResource(rname); } String s = "class=" + c + ",classloader:" + cl + ",url=" + url; s = s + ",resourceName=" + rname; s = s + "\n\n"; while (cl != null) { cl = cl.getParent(); s = s + cl + "\n"; } return s; } public static String getResourceName(Class clazz) { if (null == clazz) { return "class is null"; } String cname = clazz.getName(); String[] arr = cname.split("\\."); String rname = ""; int len = arr.length; for (int i = 0; i < len; i++) { if (i > 0) { rname = rname + "/"; } rname = rname + arr[i]; } rname = rname + ".class"; return rname; } share-utils.jar 包含 ShareUtils.class 类加载顺序 ${JAVA_HOME}/jre/lib/ext java classpath ${webapp}/WEB-INF/classes ${webapp}/WEB-INF/lib ${tomcat.home}/lib bootstrap class loader 引导类加载器 加载java核心类库 不是java.lang.ClassLoader的实例 ExtClassLoader 的父加载器为 bootstrap class loader 但是 getParent()拿到是null 把 share-utils.jar 或 ShareUtils.class 依次从相应的目录移除 以下为各种类加载情况日志记录 1 ExtClassLoader ${JAVA_HOME}/jre/lib/ext class=class com.dyyx.ShareUtils,classloader:sun.misc.Launcher$ExtClassLoader@addbf1,url=jar:file:/D:/soft/jdk1.6.0_21/jre/lib/ext/share-utils.jar!/com/dyyx/ShareUtils.class,resourceName=com/dyyx/ShareUtils.class null 2 AppClassLoader java classpath class=class com.dyyx.ShareUtils,classloader:sun.misc.Launcher$AppClassLoader@19821f,url=jar:file:/D:/tomcat6min/bin/share-utils.jar!/com/dyyx/ShareUtils.class,resource Name=com/dyyx/ShareUtils.class sun.misc.Launcher$ExtClassLoader@addbf1 null 3 WebappClassLoader ${webapp}/WEB-INF/classes class=class com.dyyx.ShareUtils,classloader:WebappClassLoader context: delegate: false repositories: /WEB-INF/classes/ ----------> Parent Classloader: org.apache.catalina.loader.StandardClassLoader@1172e08 ,url=file:/D:/soft/book/high/code/action/webroot/WEB-INF/classes/com/dyyx/ShareUtils.class,resourceName=com/dyyx/ShareUtils.class org.apache.catalina.loader.StandardClassLoader@1172e08 sun.misc.Launcher$AppClassLoader@19821f sun.misc.Launcher$ExtClassLoader@addbf1 null 4 WebappClassLoader ${webapp}/WEB-INF/lib class=class com.dyyx.ShareUtils,classloader:WebappClassLoader context: delegate: false repositories: /WEB-INF/classes/ ----------> Parent Classloader: org.apache.catalina.loader.StandardClassLoader@1172e08 ,url=jar:file:/D:/soft/book/high/code/action/webroot/WEB-INF/lib/share-utils.jar!/com/dyyx/ShareUtils.class,resourceName=com/dyyx/ShareUtils.class org.apache.catalina.loader.StandardClassLoader@1172e08 sun.misc.Launcher$AppClassLoader@19821f sun.misc.Launcher$ExtClassLoader@addbf1 null 5 StandardClassLoader ${tomcat.home}/lib class=class com.dyyx.ShareUtils,classloader:org.apache.catalina.loader.StandardClassLoader@1172e08,url=jar:file:/D:/tomcat6min/lib/share-utils.jar!/com/dyyx/ShareUtils.class,resourceName=com/dyyx/ShareUtils.class sun.misc.Launcher$AppClassLoader@19821f sun.misc.Launcher$ExtClassLoader@addbf1 null 双亲委派模型 引导类加载器 扩展类加载器 应用(系统)类加载器 自定义类加载器(L1) 自定义类加载器(L2) 自定义类加载器(Ln) ...... tomcat6类加载器示意图 http://hiphotos.baidu.com/ajf8/pic/item/3a7fe938b6003af37d7927d2352ac65c1238b6ea.jpg 原文链接 http://hi.baidu.com/ajf8/blog/item/055bac5394f386100df3e3f9.html

tomcat6类加载器与类加载顺序