如何从清单文件读取元数据 [英] How to read meta data from Manifest file

问题描述

我正在尝试从清单文件中提取信息以显示在jar文件中的一种方法中，但是似乎存在一些问题.感谢您的帮助.

I'm trying to extract information from my manifest file to display in one of the methods in my jar file, but seem to be having some issues. Any help is appreciated.

清单文件:

Manifest-Version: 1.0
Created-By: 1.8.0_60 (Oracle Corporation)
Main-Class: com.example.package1.myClass

Name: com/example/package1
Specification-Title: MyPackage
Specification-Version: v1.1
Specification-Vendor: MyCompanyName
Implementation-Title: MP
Implementation-Version: 2015-11-05-C
Implementation-Vendor: MyName

Name: com/example/package2
Specification-Title: MySecondaryPackage
Specification-Version: v2.0
Specification-Vendor: MyCompanyName
Implementation-Title: M2ndP
Implementation-Version: 2015-11-05-C
Implementation-Vendor: MyName

myClass.java:

package com.example.package1;
import com.example.package2;

class myClass {
  public static void main(String[] args) {
    try {
      myClass clz = new myClass();
      Thread.sleep(10000); //pause 10 seconnds so we can see what's spit out
    } catch (Exception e) {
    //excluded in example
    }
  }

  public myClass() {
    Package pkg = getClass().getPackage();
    if (pkg == null)
      System.out.println("No Package Found");
    else {
      System.out.println("specs: " + pkg.getSpecificationTitle() + " - " + pkg.getSpecificationVersion());
      System.out.println("imps:  " + pkg.getImplementationTitle() + " - " + pkg.getImplementationVersion());
      System.out.println("name:  " + pkg.getName());
    }
    //other code here excluded from example
  }
}

输出:

specs: null - null
imps:  null - null
name:  com.example.package1

那有什么用呢?看来pkg对象已正确定义，但它没有读取任何Specification或Implementation属性.

So what gives? It looks like the pkg object is being defined correctly, but it doesn't read any of the Specification or Implementation properties.

推荐答案

所以我终于弄清楚了，并认为我愿意和别人分享我的头撞在那堵砖墙上的情况.我从来没有得到Package类中的方法来返回null以外的任何东西.有关如何成功实现此功能，请参见下面的修订代码.

So I finally figured it out and thought I'd share incase anyone else was banging their head against the proverbial brick wall as much as I was. I never could get the methods in the Package class to return anything other than null. See revised code below for how I managed to pull it off.

package com.example.package1;
import java.util.*;
import java.util.jar.*;
import java.net.*;

class myClass {
  public static void main(String[] args) {
    try {
    new myClass();
    } catch (Exception e) {
    System.out.println(e.getMessage());
    } finally {
    System.out.println("Done");
    try{Thread.sleep(40000);}catch(Exception ee){}
    }
  }

public myClass() throws Exception {
  String clz = getClass().getSimpleName() + ".class";
  String pth = getClass().getResource(clz).toString();
  String mnf = pth.substring(0, pth.lastIndexOf("!") + 1) + "/META-INF/MANIFEST.MF";
  String pkg = getClass().getPackage().getName().replaceAll("\\.","/");
  URL url = new URL(mnf);
  Manifest manifest = new Manifest(url.openStream());

  Attributes attr = manifest.getAttributes(pkg);
  String value = attr.getValue("Specification-Title") + " - " + 
  attr.getValue("Implementation-Title") + " " + 
  attr.getValue("Specification-Version") + " build # " + 
  attr.getValue("Implementation-Version");
  System.out.println(value);
  }
}

输出:

MyPackage - MP v1.1 build # 2015-11-05-C
Done

提取四段元数据的代码很多.

Which is a lot of code to extract four pieces of Metadata.

因此，如果您希望少写几行，这就是我所使用的:

So if you like a few less lines here's what I used instead:

public myClass() throws Exception {
  Attributes attr = new Manifest(new URL(getClass().getResource(getClass().getSimpleName() + ".class").toString().substring(0, getClass().getResource(getClass().getSimpleName() + ".class").toString().lastIndexOf("!") + 1) + "/META-INF/MANIFEST.MF").openStream()).getAttributes(getClass().getPackage().getName().replaceAll("\\.","/"));
  String value = attr.getValue("Specification-Title") + " - " + attr.getValue("Implementation-Title") + " " + attr.getValue("Specification-Version") + " build # " + attr.getValue("Implementation-Version");
  System.out.println(value);
}

这篇关于如何从清单文件读取元数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！