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JAR文件是一种具有特定构造的zip文件

1.JAR文件的创建：

import java.util.jar.JarEntry;

import java.util.jar.JarOutputStream;

import java.util.jar.Manifest;

import java.io.File;

import java.io.FileOutputStream;

import java.io.FileInputStream;

import java.io.IOException;

public class JarCreate {

    public static void main(String arg[]) {

        JarCreate zc = new JarCreate();

        zc.create("testfile.jar",arg);

    }

    public void create(String jarfilename,String filename[]) {

        byte block[] = new byte[256];

        int length;

        try {

            //FileInputStream->Manifest->JarOutputStream

     //                                                                ^

     //                                                                 |

     //                                                    FileOutputStream

            FileInputStream fis = new FileInputStream("manifest");

            Manifest man = new Manifest(fis);//创建manifest文件

            FileOutputStream fos = new FileOutputStream(jarfilename);

            JarOutputStream out = new JarOutputStream(fos,man);

            for(int i=0; i<filename.length; i++) {

                FileInputStream in = new FileInputStream(filename[i]);

                String name = filename[i].replace(File.separatorChar,'/');

                JarEntry jarentry = new JarEntry(name);

                out.putNextEntry(jarentry);

                //FileInputStream->FileOutputStream

                while((length = in.read(block)) > 0)

                    out.write(block,0,length);

                out.closeEntry();

                in.close();

            }

            out.close();

        } catch(IOException e) {

            System.out.println(e);

        }

    }

}

2.JAR文件的读取

import java.util.jar.JarFile;

import java.util.jar.JarEntry;

import java.util.Enumeration;

import java.io.IOException;

public class JarList {

    public static void main(String arg[]) {

        JarList zl = new JarList();

        zl.list("testfile.jar");

    }

    public void list(String filename) {

        try {

            JarFile jarfile = new JarFile(filename);

Enumeration entrylist = jarfile.entries();

            while(entrylist.hasMoreElements()) {

                JarEntry jarentry = (JarEntry)entrylist.nextElement();

                System.out.println(jarentry.getName());

            }

            jarfile.close();

        } catch(IOException e) {

            System.out.println(e);

        }

    }

}

3.JAR文件的解压

import java.util.jar.JarFile;

import java.util.jar.JarEntry;

import java.util.Enumeration;

import java.io.InputStream;

import java.io.FileOutputStream;

import java.io.IOException;

public class JarExtract {

    public static void main(String arg[]) {

        JarExtract ze = new JarExtract();

        ze.extract("testfile.jar");

    }

    public void extract(String jarfilename) {

        byte block[] = new byte[256];

        int length;

        try {

            JarFile jarfile = new JarFile(jarfilename);

            Enumeration entrylist = jarfile.entries();

            while(entrylist.hasMoreElements()) {

                JarEntry jarentry = (JarEntry)entrylist.nextElement();

                InputStream in = jarfile.getInputStream(jarentry);

                String newfilename = jarentry.getName();

                FileOutputStream out = new FileOutputStream(newfilename);

                while((length = in.read(block)) > 0)

                    out.write(block,0,length);

                in.close();

                out.close();

            }

        } catch(IOException e) {

            System.out.println(e);

        }

    }

}

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