用于读取和显示Java .class版本的工具

Do any of you know of a tool that will search for .class files and then display their compiled versions?

您是否知道有一个工具可以搜索.class文件，然后显示它们的编译版本?

I know you can look at them individually in a hex editor but I have a lot of class files to look over (something in my giant application is compiling to Java6 for some reason).

我知道您可以在十六进制编辑器中单独查看它们，但是我有许多类文件需要查看(出于某种原因，我的大型应用程序中的一些内容正在编译为Java6)。

7 个解决方案

#1

133

Use the javap tool that comes with the JDK. The -verbose option will print the version number of the class file.

使用JDK附带的javap工具。-verbose选项将打印类文件的版本号。

> javap -verbose MyClass
Compiled from "MyClass.java"
public class MyClass
  SourceFile: "MyClass.java"
  minor version: 0
  major version: 46
...

To only show the version:

只显示版本:

WINDOWS> javap -verbose MyClass | find "version"
LINUX  > javap -verbose MyClass | grep version

#2

It is easy enough to read the class file signature and get these values without a 3rd party API. All you need to do is read the first 8 bytes.

读取类文件签名并在没有第三方API的情况下获取这些值非常容易。你所需要做的就是读取前8个字节。

ClassFile {
    u4 magic;
    u2 minor_version;
    u2 major_version;

For class file version 51.0 (Java 7), the opening bytes are:

对于类文件51.0 (Java 7)，打开的字节为:

CA FE BA BE 00 00 00 33

...where 0xCAFEBABE are the magic bytes, 0x0000 is the minor version and 0x0033 is the major version.

…0xCAFEBABE是神奇的字节，0x0000是次要版本，0x0033是主要版本。

import java.io.*;

public class Demo {
  public static void main(String[] args) throws IOException {
    ClassLoader loader = Demo.class.getClassLoader();
    try (InputStream in = loader.getResourceAsStream("Demo.class");
        DataInputStream data = new DataInputStream(in)) {
      if (0xCAFEBABE != data.readInt()) {
        throw new IOException("invalid header");
      }
      int minor = data.readUnsignedShort();
      int major = data.readUnsignedShort();
      System.out.println(major + "." + minor);
    }
  }
}

Walking directories (File) and archives (JarFile) looking for class files is trivial.

查找类文件的行走目录(文件)和归档(JarFile)是微不足道的。

Oracle's Joe Darcy's blog lists the class version to JDK version mappings up to Java 7:

Oracle的Joe Darcy的博客列出了JDK版本映射到Java 7的类版本:

Target   Major.minor Hex
1.1      45.3        0x2D
1.2      46.0        0x2E
1.3      47.0        0x2F
1.4      48.0        0x30
5 (1.5)  49.0        0x31
6 (1.6)  50.0        0x32
7 (1.7)  51.0        0x33
8 (1.8)  52.0        0x34
9        53.0        0x35

#3

On Unix-like

在类unix

file /path/to/Thing.class

Will give the file type and version as well. Here is what the output looks like:

将提供文件类型和版本。下面是输出的样子:

compiled Java class data, version 49.0

编译Java类数据，版本49.0

#4

If you are on a unix system you could just do a

如果你在unix系统上，你可以做一个

find /target-folder -name \*.class | xargs file | grep "version 50\.0"

(my version of file says "compiled Java class data, version 50.0" for java6 classes).

(我的文件版本是“编译Java类数据，版本50.0”用于java6类)。

#5

Yet another java version check

另一个java版本检查。

od -t d -j 7 -N 1 ApplicationContextProvider.class | head -1 | awk '{print "Java", $2 - 44}'

#6

In eclipse if you don't have sources attached. Mind the first line after the attach source button.

在eclipse中，如果没有附加源代码。注意附加源按钮后的第一行。

// Compiled from CDestinoLog.java (version 1.5 : 49.0, super bit)

/ /从CDestinoLog编译。java(版本1.5:49.0，超级位)

#7

Maybe this helps somebody, too. Looks there is more easy way to get JAVA version used to compile/build .class. This way is useful to application/class self check on JAVA version.

也许这对某些人也有帮助。看起来有更简单的方法可以让JAVA版本用于编译/构建.class。这种方法对于JAVA版本的应用程序/类自我检查非常有用。

I have gone through JDK library and found this useful constant: com.sun.deploy.config.BuiltInProperties.CURRENT_VERSION. I do not know since when it is in JAVA JDK.

我浏览了JDK库，发现了这个有用的常量:com.sun. deployment .config. build . current_version。我不知道它什么时候在JAVA JDK中。

Trying this piece of code for several version constants I get result below:

为几个版本常量尝试这段代码，我得到以下结果:

src:

src:

System.out.println("JAVA DEV       ver.: " + com.sun.deploy.config.BuiltInProperties.CURRENT_VERSION);
System.out.println("JAVA RUN     v. X.Y: " + System.getProperty("java.specification.version") );
System.out.println("JAVA RUN v. W.X.Y.Z: " + com.sun.deploy.config.Config.getJavaVersion() ); //_javaVersionProperty
System.out.println("JAVA RUN  full ver.: " + System.getProperty("java.runtime.version")  + " (may return unknown)" );
System.out.println("JAVA RUN       type: " + com.sun.deploy.config.Config.getJavaRuntimeNameProperty() );

output:

输出:

JAVA DEV       ver.: 1.8.0_77
JAVA RUN     v. X.Y: 1.8
JAVA RUN v. W.X.Y.Z: 1.8.0_91
JAVA RUN  full ver.: 1.8.0_91-b14 (may return unknown)
JAVA RUN       type: Java(TM) SE Runtime Environment

In class bytecode there is really stored constant - see red marked part of Main.call - constant stored in .class bytecode

在类字节码中确实存储了常量——参见Main的红色标记部分。调用-常量存储在.class字节码中

Constant is in class used for checking if JAVA version is out of date (see How Java checks that is out of date)...

常量在类中用于检查JAVA版本是否过时(参见JAVA如何检查过期)……

#1

133