打好jar包之后还需要更改清单文件的.

打开生成的jar,里面有一个MANIFEST.MF的文件把它打开.

然后有一行Main-Class，没有就加上。如：

Manifest-Version: 1.0

Main-Class: 类的全地址

要在后面加上你的主main class文件.比如你的文件是HelloWrold.java编译后就是HelloWrold.class.那么这里就写HelloWrold.然后回车,

Main-Class: com.HelloWrold

注意一定要在名字后面有一个回车让光标到下一行.

这样你生成的jar包才能找到你的主class去运行

用工具打包的时候最后一步，选择Main calss的路径地址。

例子：MANIFEST.MF

Manifest-Version: 1.0

Main-Class: com.MD5File

执行： java -jar getMD5File.jar c:\systeminfo.txt

代码如下：

package com;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

public class MD5File {

protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

// private ReadBufferBean readBufferBean;

protected MessageDigest messagedigest = null;

public MD5File() {

try {

messagedigest = MessageDigest.getInstance("MD5");

} catch (NoSuchAlgorithmException e) {

// log.error(MD5File.class.getName()+

// "初始化失败，MessageDigest不支持MD5Util。", e);

messagedigest = null;

}

}

public void putContent(byte[] b) {

putContent(b, 0, b.length);

}

public void putContent(byte[] b, int start, int length) {

if (messagedigest != null)

messagedigest.update(b, start, length);

}

public String bufferToHex() {

String md5_value = bufferToHex(messagedigest.digest());

return md5_value;

}

/**

* 生成文件的md5校验值

*

* @param file

* @return

* @throws IOException

*/

public String getFileMD5String(File file) throws IOException {

InputStream fis = null;

try {

fis = new FileInputStream(file);

byte[] buffer = new byte[1024];

int numRead = 0;

while ((numRead = fis.read(buffer)) > 0) {

messagedigest.update(buffer, 0, numRead);

}

} finally {

if (fis != null)

try {

fis.close();

} catch (IOException e) {

// log.error("close error file:"+file.getAbsolutePath(),e);

}

}

return bufferToHex(messagedigest.digest());

}

private String bufferToHex(byte bytes[]) {

return bufferToHex(bytes, 0, bytes.length);

}

private String bufferToHex(byte bytes[], int m, int n) {

StringBuffer stringbuffer = new StringBuffer(2 * n);

int k = m + n;

for (int l = m; l < k; l++) {

appendHexPair(bytes[l], stringbuffer);

}

return stringbuffer.toString();

}

private void appendHexPair(byte bt, StringBuffer stringbuffer) {

char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换, >>>

// 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同

char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换

stringbuffer.append(c0);

stringbuffer.append(c1);

}

public static void main(String[] args) throws IOException {

long begin = System.currentTimeMillis();

MD5File md5 = new MD5File();

//  File file = new File("c:\\systeminfo.txt");

File file = new File(args[0]);

String md5str = md5.getFileMD5String(file);

System.out.println(md5str);

// String md5 = getFileMD5String(file);

// String md5 = getMD5String("a");

long end = System.currentTimeMillis();

System.out.println("md5:" + md5str + " time:" + ((end - begin) / 1000) + "s");

}

}