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查询java 类加载的路径
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在Spring 3.x企业应用开发实战中看到一个能经常用到的jsp，记录下，查看类的加载路径，
在jar包冲突引起的奇葩问题时很好用。使用方法
srcAdd.jsp?className=java.net.URL
<%@page contentType="text/html; charset=GBK"%>
<%@page import="java.security.*,java.net.*,java.io.*"%>
<%! public static URL getClassLocation(final Class cls) {
if (cls == null)throw new IllegalArgumentException("null input: cls");
URL result = null;
final String clsAsResource = cls.getName().replace('.', '/').concat(".class");
final ProtectionDomain pd = cls.getProtectionDomain();
// java.lang.Class contract does not specify if 'pd' can ever be null;
// it is not the case for Sun's implementations, but guard against null
// just in case:
if (pd != null) {
final CodeSource cs = pd.getCodeSource();
// 'cs' can be null depending on the classloader behavior:
if (cs != null) result = cs.getLocation();
if (result != null) {
// Convert a code source location into a full class file location
// for some common cases:
if ("file".equals(result.getProtocol())) {
try {
if (result.toExternalForm().endsWith(".jar") ||
result.toExternalForm().endsWith(".zip"))
result = new URL("jar:".concat(result.toExternalForm())
.concat("!/").concat(clsAsResource));
else if (new File(result.getFile()).isDirectory())
result = new URL(result, clsAsResource);
}
catch (MalformedURLException ignore) {}
}
}
}
if (result == null) {
// Try to find 'cls' definition as a resource; this is not
// document．d to be legal, but Sun's implementations seem to //allow this:
final ClassLoader clsLoader = cls.getClassLoader();
result = clsLoader != null ?
clsLoader.getResource(clsAsResource) :
ClassLoader.getSystemResource(clsAsResource);
}
return result;
}
%>
<html>
<head>
<title>srcAdd.jar</title>
</head>
<body bgcolor="#ffffff">
使用方法，className参数为类的全名，不需要.class后缀，如
srcAdd.jsp?className=java.net.URL
<%
try
{
String classLocation = null;
String error = null;
String className = request.getParameter("className"); classLocation = ""+getClassLocation(Class.forName(className));
if (error == null) {
out.print("类" + className + "实例的物理文件位于：");
out.print("<hr>");
out.print(classLocation);
}
else {
out.print("类" + className + "没有对应的物理文件。<br>");
out.print("错误：" + error);
}
}catch(Exception e)
{
out.print("异常。"+e.getMessage());
}
%>
</body>
</html>
