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 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;
 }
}