java中如何判断类的重复加载

来源：互联网发布：数据对比用什么图表编辑：程序博客网时间：2024/04/30 08:13

这几天在看dubbo的源码，看到里面有一个方法是检测类的重复加载的，感觉挺实用的，写下来，防备自己忘记

package com.test;import java.net.URL;import java.util.Enumeration;import java.util.HashSet;import java.util.Set;public class VersionTest {public void checkDuplicate(String path, boolean failOnError){try {// 在ClassPath搜文件Enumeration<URL> urls = VersionTest.class.getClassLoader().getResources(path);Set<String> files = new HashSet<String>();while (urls.hasMoreElements()) {URL url = urls.nextElement();if (url != null) {String file = url.getFile();if (file != null && file.length() > 0) {files.add(file);}}}// 如果有多个，就表示重复if (files.size() > 1) {                String error = "Duplicate class " + path + " in " + files.size() + " jar " + files;                if (failOnError) {                    throw new IllegalStateException(error);                } else {   System.out.println(error);                }}} catch (Throwable e) { // 防御性容错e.printStackTrace();}}//获取版本号    public static String getVersion(Class<?> cls, String defaultVersion) {        try {            // 首先查找MANIFEST.MF规范中的版本号            String version = cls.getPackage().getImplementationVersion();            if (version == null || version.length() == 0) {                version = cls.getPackage().getSpecificationVersion();            }            if (version == null || version.length() == 0) {                // 如果规范中没有版本号，基于jar包名获取版本号                CodeSource codeSource = cls.getProtectionDomain().getCodeSource();                if(codeSource == null) {                    logger.info("No codeSource for class " + cls.getName() + " when getVersion, use default version " + defaultVersion);                }                else {                    String file = codeSource.getLocation().getFile();                    if (file != null && file.length() > 0 && file.endsWith(".jar")) {                        file = file.substring(0, file.length() - 4);                        int i = file.lastIndexOf('/');                        if (i >= 0) {                            file = file.substring(i + 1);                        }                        i = file.indexOf("-");                        if (i >= 0) {                            file = file.substring(i + 1);                        }                        while (file.length() > 0 && ! Character.isDigit(file.charAt(0))) {                            i = file.indexOf("-");                            if (i >= 0) {                                file = file.substring(i + 1);                            } else {                                break;                            }                        }                        version = file;                    }                }            }            // 返回版本号，如果为空返回缺省版本号            return version == null || version.length() == 0 ? defaultVersion : version;        } catch (Throwable e) { // 防御性容错            // 忽略异常，返回缺省版本号            logger.error("return default version, ignore exception " + e.getMessage(), e);            return defaultVersion;        }    }public static void main(String[] args) {new VersionTest().checkDuplicate("com/spring/schema/spring_schema/entity/People.class",false);}}

输出的结果为：

Duplicate class com/spring/schema/spring_schema/entity/People.class in 2 jar [file:/D:/workspacelianxi/spring-schema/src/spring-schema-0.0.1-SNAPSHOT.jar!/com/spring/schema/spring_schema/entity/People.class, /D:/workspacelianxi/spring-schema/target/classes/com/spring/schema/spring_schema/entity/People.class]

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