如何使用Package类的getImplementationVersion（）方法从JAR的清单中获取包版本 [英] How to obtain a package version from the JAR's manifest, using the getImplementationVersion() method of the Package class

问题描述

当我准备我的程序进行部署时，我将它与Eclipse jar-in-jar类加载器一起打包到JAR中。当我的程序从JAR运行时，我需要知道一个包的版本，但我不能从jar的清单中以简单和诚实的方式获取它。
清单如下所示：

When I prepare my program for deployment, I pack it into a JAR, along with the Eclipse jar-in-jar class loader. When my program runs from the JAR, I need to know a package's version, but I can not obtain it from the jar's manifest a simple and "honest" way. The manifest looks like this:

 Manifest-Version: 1.0
 Created-By: 1.8.0_73-b02 (Oracle Corporation)
 Main-Class: org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader
 Rsrc-Main-Class: com.domain.sp2.controller.Controller
 Rsrc-Class-Path: ./ jar-in-jar-loader.zip javahelp-2.0.05.jar json-simple-1.1.1.jar
 Class-Path: .

 Name: com/domain/sp2/controller/
 Implementation-Version: 19

要获得软件包的实现版本，我尝试使用最简单直接的方法：

To obtain the package's implementation version, I try to use the simplest and straight-forward way:

package com.domain.sp2.controller;
public class Controller {
...
   public static String getBuildNumber() throws IOException {
     Package pckg = Controller.class.getPackage();
     pr(pckg.getName());    // prints "com.domain.sp2.controller", as expected 
     return pckg.getImplementationVersion();   // returns null
   }  
...
}

根据 http://docs.oracle.com/javase/tutorial/ deployment / jar / packageman.html 和 http://docs.oracle.com/javase/8/docs/api/java/lang/Package.html#getImplementationVersion-- （和其他来源），它应该返回19，但它返回null。对于JRE库的包，它返回正确的值。也许我错过了关于如何在清单中命名包的详细信息，或者与 JarRsrcLoader 相关的原因 - 可能需要一些特殊的语法来解决包。我也试过。com / domain /...\"，/ com / domain /...\"和... / controller，甚至rsrc：./ com / domain ...作为清单中的包名称 - 一切都没有成功。我可以使用其他方式，例如将清单加载为流并使用Manifest类解析它，但我想了解使用 getImplementationVersion（）方法的正确方法。

According to http://docs.oracle.com/javase/tutorial/deployment/jar/packageman.html and http://docs.oracle.com/javase/8/docs/api/java/lang/Package.html#getImplementationVersion-- (and other sources), it should return "19", but it returns null. For the packages of the JRE libraries, it returns correct values. Perhaps I have missed a detail about how to name the package in the manifest, or the reason pertains to the JarRsrcLoader - may be it requires some special syntax to address packages. I have also tried ".com/domain/...", "/com/domain/..." and ".../controller", and even "rsrc:./com/domain..." as the package name in the manifest - all without success. I could use other ways, e.g. to load the manifest as stream and parse it with the Manifest class, yet I would like to understand what is the correct way to use the getImplementationVersion() method.

推荐答案

您可以从classLoader中读取清单文件，并获得您需要的值，如下所示：

You can read the manifest file from the classLoader and get the value you need as below:

URLClassLoader cl = (URLClassLoader) YOUR_CLASS.class.getClassLoader();
try {
  URL url = cl.findResource("META-INF/MANIFEST.MF");
  Manifest manifest = new Manifest(url.openStream());
  Attributes mainAttributes = manifest.getMainAttributes();
  String implVersion = mainAttributes.getValue("Implementation-Version");

  System.out.println(implVersion);
} catch (IOException E) {
      // handle
}

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