验证Java版本兼容性 [英] Verify java version compatibility

问题描述

我有一个使用jdk 1.7编译的jar文件，我想在加载期间检查我的jar运行的Java运行时环境是1.7还是更高版本.有办法吗?

I have a jar file compiled using jdk 1.7, I'd like to check during load time that the java runtime environment my jar is running under is 1.7 or newer. Is there a way to do that?

我尝试使用System.getProperty("java.version")，但这没有帮助，因为我的类版本是51，而jre 1.6拒绝加载它.

I tried using System.getProperty("java.version") but that didn't help since my class version was 51 and jre 1.6 refuse to load it.

推荐答案

我有相同的要求，并通过以下方式解决了该问题:

I have the same requirement and I solved it the following way:

具有一个启动"类，该类绝对不依赖于(=导入)任何新的JDK类或您的应用程序的任何类.您不按名称导入您的主班！

Have a "startup" class that has absolutely no dependencies (=imports) to any new JDK class or to any of your application's classes. You man not import your main class by name!

类似:

在该启动程序类中，检查所需的Java版本.

Inside that starter class, check the Java version that you need.

如果检查成功，则使用反射加载您的主类并启动它的main方法(或您使用的任何方法).像这样:

If the check is successful then load your main class using reflection and start it's main method (or whichever method you use). Something like this:

public class MyStarter
{
   public static void main(String[] args)
   {
      String version = System.getProperty("java.version", null);
      boolean isVersionOK = ... ; 

      if (!isVersionOK)
      {
         System.err.println("Wrong Java version detected");
         // or display some messagebox using JOptionPane
         System.exit(1);
      }

      Class mainClass = Class.forName("com.foo.MyMain");
      Method main = mgr.getDeclaredMethod("main", new Class[] { String[].class });
      main.invoke(null, new Object[] { args });
   }
}

再次:确保MyStarter不包含任何导入到您的应用程序或Java 1.2(或您要定位的任何Java版本)中不可用的类.

Again: make sure MyStarter does not contain any imports to your application or classes that are not available in Java 1.2 (or whatever Java version you will target).

然后使用 -source 1.2 -target 1.2 编译 MyStarter (并且仅该类)使用常规编译器编译其余的类(例如，创建Java7 .class文件).

Then compile MyStarter (and only that class) with -source 1.2 -target 1.2 Compile the rest of your classes with the regular compiler (e.g. creating Java7 .class files).

如果生成可执行jar，则将 com.foo.MyStarter 添加为 Main-Class:属性.

If you generate an executable jar, then add com.foo.MyStarter as the Main-Class: attribute.

我的Ant build.xml 中的编译"目标看起来像这样:

My the "compile" target in my Ant build.xml looks something like this:

<-- compile the starter class for Java 1.2 -->
<javac destdir="${build}"
       srcdir="${src}"
       target="1.2"
       source="1.2"
       encoding="ISO-8859-1"
       includeantruntime="false"
       includes="com/foo/MyStarter.java"/>  

<-- compile the rest with for Java 1.6 -->
<javac destdir="${build}"
       srcdir="${src}"
       target="1.6"
       source="1.6"
       includeantruntime="false"
       encoding="ISO-8859-1">
  <exclude name="com/foo/MyStarter.java"/>
  <classpath>
      ....
  </classpath>
</javac>

然后将所有内容放入一个jar文件中.

Then put everything into one jar file.

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