Question

如何查看class文件编译的jdk版本

Answer 1

在jar包中，用winrar解压一个类文件，然后在命令行下面输入
javap -verbose classname
会输出一些信息，大致如下:

Compiled from "HtmlCrawer.java"
public class org.eagleeye.html.HtmlCrawer extends java.lang.Object
SourceFile: "HtmlCrawer.java"
minor version: 0
major version: 50
Constant pool:
const #1 = class #2; // org/eagleeye/html/HtmlCrawer
const #2 = Asciz org/eagleeye/html/HtmlCrawer;
const #3 = class #4; // java.lang/Object
const #4 = Asciz java.lang/Object;
const #5 = Asciz client;
....

后面省略了，可以看到前面有两行:
minor version: 0
major version: 50
表示了类文件的版本

Answer 2

javap
javap