這幾天在看dubbo的原始碼，看到裡面有一個方法是檢測類的重複載入的，感覺挺實用的，寫下來，防備自己忘記

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搜檔案
			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);
					}
				}
			}
			// 如果有多個，就表示重複
			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) { // 防禦性容錯
			e.printStackTrace();
		}
	}
	//獲取版本號
    public static String getVersion(Class<?> cls, String defaultVersion) {
        try {
            // 首先查詢MANIFEST.MF規範中的版本號
            String version = cls.getPackage().getImplementationVersion();
            if (version == null || version.length() == 0) {
                version = cls.getPackage().getSpecificationVersion();
            }
            if (version == null || version.length() == 0) {
                // 如果規範中沒有版本號，基於jar包名獲取版本號
                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;
                    }
                }
            }
            // 返回版本號，如果為空返回預設版本號
            return version == null || version.length() == 0 ? defaultVersion : version;
        } catch (Throwable e) { // 防禦性容錯
            // 忽略異常，返回預設版本號
            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);
	}
}
 

輸出的結果為：

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]