如何从清单文件中读取元数据

Question

我正在尝试从我的清单文件中提取信息以显示在我的 jar 文件中的一种方法中，但似乎遇到了一些问题。感谢任何帮助。

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

那么是什么原因呢？看起来 pkg 对象定义正确，但它没有读取任何规范或实现属性。

Answer 1

所以我终于弄明白了，我想我会分享，以防其他人像我一样用头撞在众所周知的砖墙上。除了 null 之外，我永远无法获得 Package class 到 return 中的方法。请参阅下面的修订代码，了解我是如何成功实现它的。

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，如果您喜欢少几行，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);
}

Answer 2

在包路径的末尾添加斜线。 IE。将 com/example/package1 更改为 com/example/package1/。在包 com.example.package1 中请求一些 class（我们称之为 Foo），一切都应该正常。

Package pkg = com.example.package1.class.getPackage();
String specVer = pkg.getSpecificationVersion();

结尾的斜杠似乎很重要。例如。这是来自 Apache ant.jar:

的清单

Name: org/apache/tools/ant/
Extension-name: org.apache.tools.ant
Specification-Title: Apache Ant
Specification-Version: 1.9.6
Specification-Vendor: Apache Software Foundation
Implementation-Title: org.apache.tools.ant
Implementation-Version: 1.9.6
Implementation-Vendor: Apache Software Foundation

Answer 3

我的做法

public class UtilReflection {
    
    public static void checkVersion(String[] args){
        if(args.length == 1 && "--info".equals(args[0])){
            try {
                InputStream inputStream = UtilReflection.class.getClassLoader().getResource("META-INF/MANIFEST.MF").openStream();
                Manifest manifest = new Manifest(inputStream);
                Attributes attrs = manifest.getMainAttributes();
                if(attrs == null){
                    throw new RuntimeException("no attributes found");
                }
                Set<Object> keys = attrs.keySet();
                for(Object key:keys){
                    System.out.println(String.format("%s: %s", key,attrs.get(key)));
                }
                
            } catch (IOException e) {
                e.printStackTrace();
            }

            java.lang.System.exit(0);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        UtilReflection.checkVersion(args);
    }
}

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