如何从清单文件读取元数据

Question

我正在尝试从清单文件中提取信息以在文件中的一种方法中显示jar，但是似乎存在一些问题。任何帮助表示赞赏。

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

那有什么呢？看起来pkg对象已正确定义，但是它不读取任何Specification或Implementation属性。

Answer 1

所以我终于弄清楚了，以为我愿意和别人分享我的头，以防其他人像我那样把头撞在那堵砖墙上。我再也无法让Package类中的方法返回除以外的任何值null。请参阅下面的修订代码，以了解如何实现这一目标。

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。

因此，如果您希望少写几行，这就是我使用的：

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);
}