java获取版本号及字节码编译版本方法示例

package com.jinggujin.util;import java.io.DataInputStream;import java.io.File;import java.io.FileInputStream;import java.io.InputStream;import java.util.Enumeration;import java.util.jar.JarEntry;import java.util.jar.JarFile;/** * Java 版本工具 *  * @author jianggujin * */public class JavaVersionUtils{ private static final int JAVA_CLASS_MAGIC = 0xCAFEBABE; public final static int JDK_1_2 = 46; public final static int JDK_1_3 = 47; public final static int JDK_1_4 = 48; public final static int JDK_5 = 49; public final static int JDK_6 = 50; public final static int JDK_7 = 51; public final static int JDK_8 = 52; /** * 获得当前环境JDK版本 *  * @return */ public static int getJDKVersion() { String version = System.getProperty("java.version"); if (version != null && version.matches("1//.//d.*")) {  int v = Integer.parseInt(version.charAt(2) + "");  if (v >= 2)  {  return 44 + v;  } } return -1; } /** * 获得class或jar编译版本 *  * @param file * @return * @throws Exception */ public static int getCompileVersion(File file) throws Exception { if (file == null || !file.isFile() || !file.getName().matches(".*//.((jar)|(class))")) {  throw new IllegalArgumentException("the file must be a jar or class."); } int version = -1; if (file.getName().endsWith("jar")) {  JarFile jarFile = new JarFile(file);  Enumeration<JarEntry> enumeration = jarFile.entries();  while (enumeration.hasMoreElements())  {  JarEntry entry = enumeration.nextElement();  if (entry.getName().endsWith(".class"))  {  InputStream in = jarFile.getInputStream(entry);  version = getVersion(in);  in.close();  break;  }  }  jarFile.close(); } else {  InputStream in = new FileInputStream(file);  version = getVersion(in);  in.close(); } return version; } private static int getVersion(InputStream in) throws Exception { DataInputStream dis = new DataInputStream(in); // ，前面8个字节CA FE BA BE 是固定的，之后4个字节是次版本号，次版本号后面的4个字节是jdk的版本号 int magic = dis.readInt(); if (magic == JAVA_CLASS_MAGIC) {  // int minorVersion =  dis.readUnsignedShort();  int majorVersion = dis.readUnsignedShort();  // Java 1.2 >> 46  // Java 1.3 >> 47  // Java 1.4 >> 48  // Java 5 >> 49  // Java 6 >> 50  // Java 7 >> 51  // Java 8 >> 52  return majorVersion; } return -1; }}