解压jar，获取xxx.calss文件

dos命令行javap -verbose classname

import java.io.InputStream;import java.io.PrintWriter;public class CMD命令 {    public static void main(String[] args) {        String filePath = "D:/git/new_baiwang/sdk-java/sdk-java/target/classes/com/baiwang/bop/Constants.class";        docmd(filePath);    }    static void docmd(String filePath) {        String[] command = { "cmd", };        Process p = null;        try {            p = Runtime.getRuntime().exec(command);            new Thread(new SyncPipe(p.getInputStream())).start();            new Thread(new SyncPipe(p.getErrorStream())).start();            PrintWriter stdin = new PrintWriter(p.getOutputStream());            String ml = "javap -verbose " + filePath;            stdin.println(ml);            stdin.close();        } catch (Exception e) {            throw new RuntimeException("编译出现错误：" + e.getMessage());        }    }}class SyncPipe implements Runnable {    private final InputStream istrm_;    public SyncPipe(InputStream istrm) {        istrm_ = istrm;    }    public void run() {        try {            final byte[] buffer = new byte[10240];            StringBuffer sbf = new StringBuffer();            for (int length = 0; (length = istrm_.read(buffer)) != -1;) {                sbf.append(new String(buffer, 0, length));            }            String msg = sbf.toString();            if (msg.length() > 10) {                if (msg.contains("major version: 50")) {                    System.out.println("编译的JDK版本是1.6");                } else if (msg.contains("major version: 51")) {                    System.out.println("编译的JDK版本是1.7");                } else if (msg.contains("major version: 52")) {                    System.out.println("编译的JDK版本是1.8");                } else {                    System.err.println("运行错误，未知版本！");                    System.out.println(msg);                }            } else {                System.err.println("运行错误，没有想要的信息！");            }        } catch (Exception e) {            throw new RuntimeException("处理命令出现错误：" + e.getMessage());        }    }}