用于找出编译类文件的JDK版本的Java API？
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Java API to find out the JDK version a class file is compiled for?
提问by Prabhu R
Are there any Java APIs to find out the JDK version a class file is compiled for? Of course there is the javap tool to find out the major version as mentioned in here. However I want to do it programmatically so that that I could warn the user to compile it for the appropriate JDK
是否有任何 Java API 可以找出编译类文件的 JDK 版本？当然有 javap 工具来找出这里提到的主要版本。但是我想以编程方式进行，以便我可以警告用户为适当的 JDK 编译它
采纳答案by RealHowTo
import java.io.*;
public class ClassVersionChecker {
public static void main(String[] args) throws IOException {
for (int i = 0; i < args.length; i++)
checkClassVersion(args[i]);
}
private static void checkClassVersion(String filename)
throws IOException
{
DataInputStream in = new DataInputStream
(new FileInputStream(filename));
int magic = in.readInt();
if(magic != 0xcafebabe) {
System.out.println(filename + " is not a valid class!");;
}
int minor = in.readUnsignedShort();
int major = in.readUnsignedShort();
System.out.println(filename + ": " + major + " . " + minor);
in.close();
}
}
The possible values are :
可能的值为：
major minor Java platform version
45 3 1.0
45 3 1.1
46 0 1.2
47 0 1.3
48 0 1.4
49 0 5
50 0 6
51 0 7
52 0 8
53 0 9
54 0 10
55 0 11
56 0 12
57 0 13
58 0 14
回答by Robert Munteanu
回答by Michael Borgwardt
This gets you the contents of the class file:
这会让您获得类文件的内容：
MysteryClass.class.getResourceAsStream("MysteryClass.class")
MysteryClass.class.getResourceAsStream("MysteryClass.class")
Then look at bytes 5-8 to get the minor and major version. A mapping between those numbers and the JDK releases can be found here.
然后查看字节 5-8 以获取次要和主要版本。可以在此处找到这些数字与 JDK 版本之间的映射。
回答by basszero
Just read the class file directly. It's VERY easy to figure out the version. Check out the the specand wikiand then try the code. Wrapping this code and making is more useful/pretty is left as an exercise. Alternatively, you could use a library like BCEL, ASM, or JavaAssist
直接读取类文件即可。很容易找出版本。查看规范和维基，然后尝试代码。包装此代码并制作更有用/漂亮作为练习。或者，您可以使用像BCEL、ASM或JavaAssist这样的库
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class ClassVersionTest
{
private static final int JAVA_CLASS_MAGIC = 0xCAFEBABE;
public static void main(String[] args)
{
try
{
DataInputStream dis = new DataInputStream(new FileInputStream("Test.class"));
int magic = dis.readInt();
if(magic == JAVA_CLASS_MAGIC)
{
int minorVersion = dis.readUnsignedShort();
int majorVersion = dis.readUnsignedShort();
/**
* majorVersion is ...
* J2SE 6.0 = 50 (0x32 hex),
* J2SE 5.0 = 49 (0x31 hex),
* JDK 1.4 = 48 (0x30 hex),
* JDK 1.3 = 47 (0x2F hex),
* JDK 1.2 = 46 (0x2E hex),
* JDK 1.1 = 45 (0x2D hex).
*/
System.out.println("ClassVersionTest.main() " + majorVersion + "." + minorVersion);
}
else
{
// not a class file
}
}
catch (FileNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
回答by McDowell
回答by skaffman
Apache BCELprovides this API:
Apache BCEL提供了这个 API：
JavaClass c = Repository.lookupClass("com.x.MyClass")
c.getMinor();
c.getMajor();
回答by rickumali
basszero's approach can be done via the UNIX command line, and the "od(1)" command:
basszero 的方法可以通过 UNIX 命令行和“od(1)”命令完成：
% od -x HelloWorldJava.class |head -2
0000000 feca beba 0000 3100 dc00 0007 0102 2a00
0000020 6f63 2f6d 6e65 6564 6163 642f 6d65 2f6f
"feca beba" is the magic number. The "0000 3100" is 0x31, which represents J2SE 5.0.
“feca beba”是神奇的数字。“0000 3100”是 0x31，代表 J2SE 5.0。
回答by Daniel Wille
On Linux, you can use the filecommand on a class file, which I found easiest for my use case. For example:
在 Linux 上，您可以file在类文件上使用该命令，我发现这对我的用例来说是最简单的。例如：
$ file Foo.class
Foo.class: compiled Java class data, version 50.0 (Java 1.6)
