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查询java 类加载的路径
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>
查询java 类加载的路径
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