javaconvert在哪个包_Java查看JVM从哪个JAR包中加载指定类

背景方式一方式二

背景

有的时候&＃xff0c;我们经常会碰到java.lang.NoSuchMethodError的错误信息。  究其根源&＃xff0c;是由于JVM的 全盘负责委托机制导致的。  关于 全盘负责委托机制 &＃xff0c;请查看另一篇博文 全盘负责委托机制

特别是对于一些web项目&＃xff0c;jar包很多&＃xff0c;如何精确的查找呢&＃xff1f;

方式一

将下面的JSP文件&＃xff0c;放到web容器的根路径下&＃xff0c;启动web容器&＃xff0c;通过 http://ip:port/projectname/srcAdd.jsp?className&＃61;XXXXXX

比如&＃xff1a;

运行web项目&＃xff0c;访问

http://localhost:8080/hello-spring4/srcAdd.jsp?className&＃61;org.springframework.beans.factory.annotation.Autowired

srcAdd.jsp

public static URL getClassLocation(final Class cls) {

if (cls &＃61;&＃61; null)throw new IllegalArgumentException("null input: cls");

URL result &＃61; null;

final String clsAsResource &＃61; cls.getName().replace(&＃39;.&＃39;, &＃39;/&＃39;).concat(".class");

final ProtectionDomain pd &＃61; cls.getProtectionDomain();

// java.lang.Class contract does not specify if &＃39;pd&＃39; can ever be null;

// it is not the case for Sun&＃39;s implementations, but guard against null

// just in case:

if (pd !&＃61; null) {

final CodeSource cs &＃61; pd.getCodeSource();

// &＃39;cs&＃39; can be null depending on the classloader behavior:

if (cs !&＃61; null) result &＃61; cs.getLocation();

if (result !&＃61; 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 &＃61; new URL("jar:".concat(result.toExternalForm())

.concat("!/").concat(clsAsResource));

else if (new File(result.getFile()).isDirectory())

result &＃61; new URL(result, clsAsResource);

}

catch (MalformedURLException ignore) {}

}

}

}

if (result &＃61;&＃61; null) {

// Try to find &＃39;cls&＃39; definition as a resource; this is not

// document&＃xff0e;d to be legal, but Sun&＃39;s implementations seem to         //allow this:

final ClassLoader clsLoader &＃61; cls.getClassLoader();

result &＃61; clsLoader !&＃61; null ?

clsLoader.getResource(clsAsResource) :

ClassLoader.getSystemResource(clsAsResource);

}

return result;

}

%>

使用方法&＃xff0c;className参数为类的全名&＃xff0c;不需要.class后缀&＃xff0c;如

srcAdd.jsp?className&＃61;java.net.URL

try

{

String classLocation &＃61; null;

String error &＃61; null;

String className &＃61; request.getParameter("className");

classLocation &＃61;  ""&＃43;getClassLocation(Class.forName(className));

if (error &＃61;&＃61; null) {

out.print("类" &＃43; className &＃43; "实例的物理文件位于&＃xff1a;");

out.print("

out.print(classLocation);

}

else {

out.print("类" &＃43; className &＃43; "没有对应的物理文件。
");

out.print("错误&＃xff1a;" &＃43; error);

}

}catch(Exception e)

{

out.print("异常。"&＃43;e.getMessage());

}

%>

方式二

工具类 ClassLocationUtils.java

package com.xgj.master.ioc.classloaderUtil;

import java.io.File;

import java.net.MalformedURLException;

import java.net.URL;

import java.security.CodeSource;

import java.security.ProtectionDomain;

/**

*

* &＃64;ClassName: ClassLocationUtils

* &＃64;Description: tools to find which jar does the class come from

*

*/

public class ClassLocationUtils {

/**

* find the location of the class come from

* &＃64;param cls

* &＃64;return

*/

public static String where(final Class cls) {

if (cls &＃61;&＃61; null)throw new IllegalArgumentException("null input: cls");

URL result &＃61; null;

final String clsAsResource &＃61; cls.getName().replace(&＃39;.&＃39;, &＃39;/&＃39;).concat(".class");

final ProtectionDomain pd &＃61; cls.getProtectionDomain();

if (pd !&＃61; null) {

final CodeSource cs &＃61; pd.getCodeSource();

if (cs !&＃61; null) result &＃61; cs.getLocation();

if (result !&＃61; null) {

if ("file".equals(result.getProtocol())) {

try {

if (result.toExternalForm().endsWith(".jar") ||

result.toExternalForm().endsWith(".zip"))

result &＃61; new URL("jar:".concat(result.toExternalForm())

.concat("!/").concat(clsAsResource));

else if (new File(result.getFile()).isDirectory())

result &＃61; new URL(result, clsAsResource);

}

catch (MalformedURLException ignore) {}

}

}

}

if (result &＃61;&＃61; null) {

final ClassLoader clsLoader &＃61; cls.getClassLoader();

result &＃61; clsLoader !&＃61; null ?

clsLoader.getResource(clsAsResource) :

ClassLoader.getSystemResource(clsAsResource);

}

System.out.println(result.toString());

return result.toString();

}

}

运行查找

package com.xgj.master.ioc.classloader;

import com.xgj.master.ioc.classloaderUtil.ClassLocationUtils;

public class ClassLoaderTest {

public static void main(String[] args) {

// TODO Auto-generated method stub

ClassLocationUtils.where(java.lang.Thread.class);

}

}

运行结果&＃xff1a;