blocks|key|3080345|text|你几乎已经写好了解决方案。我希望下面的代码片段能有所帮助。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3080346|ClassLoader+cl+=+new+URLClassLoader(new+URL[]+{new+File("v1.jar").toURL()},+Thread.currentThread().getContextClassLoader());
Class<?>+clazz+=+cl.loadClass("Hello");|code-block|syntax|javascript|3080347|将v1.jar替换为v2.jar，此代码将加载版本2。|offset|length|style|CODE|3080348|entityMap^0|0|0|1|6|A|6|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

You have almost written the solution. 
I hope the following code fragment will help.

<pre><code>ClassLoader cl = new URLClassLoader(new URL[] {new File("v1.jar").toURL()}, Thread.currentThread().getContextClassLoader());
Class&lt;?&gt; clazz = cl.loadClass("Hello");
</code></pre>

Replace <code>v1.jar</code> by <code>v2.jar</code> and this code will load version #2.

blocks|key|218823|text|这取决于你打算如何处理这两个版本以及如何处理，但通常你至少可以在不同的类加载器中加载2个版本的类，然后设置Thread.contextClassloader()并播放...|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|218824|请参阅http://www.javaworld.com/javaqa/2003-06/01-qa-0606-load.html和http://docs.oracle.com/javase/jndi/tutorial/beyond/misc/classloader.html|218825|entityMap|0|LINK|mutability|MUTABLE|url|http://www.javaworld.com/javaqa/2003-06/01-qa-0606-load.html|1|http://docs.oracle.com/javase/jndi/tutorial/beyond/misc/classloader.html^0|1H|R|0|3|1O|0|1S|20|1|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@$9|V|A|W|1|X]|$9|Y|A|Z|1|10]]|E|$]]|$1|H|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]]]

it depends on what are u going to do with both versions and how, but in general you can at least load 2 version of class in different classloaders, and then set the Thread.contextClassloader() and play...

see <a href="http://www.javaworld.com/javaqa/2003-06/01-qa-0606-load.html" rel="nofollow">http://www.javaworld.com/javaqa/2003-06/01-qa-0606-load.html</a> and <a href="http://docs.oracle.com/javase/jndi/tutorial/beyond/misc/classloader.html" rel="nofollow">http://docs.oracle.com/javase/jndi/tutorial/beyond/misc/classloader.html</a>

blocks|key|3080393|text|你走对了路。你必须考虑到一些事情。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3080394|正常的事情是使用父类加载器中存在的类。因此，如果你想要两个版本，这些类就不能存在。|3080395|但是如果你想进行交互，你可以使用反射，或者更好的通用接口。因此，我将这样做：|3080396|common.jar:
BaseInterface

v1.jar:
SomeImplementation+implements+BaseInterface

v2.jar:
OtherImplementation+implements+BaseInterface

command-line:
java+-classpath+common.jar+YourMainClass
//+you+don't+put+v1+nor+v2+into+the+parent+classloader+classpath

Then+in+your+program:

loader1+=+new+URLClassLoader(new+URL[]+{new+File("v1.jar").toURL()},+Thread.currentThread().getContextClassLoader());
loader2+=+new+URLClassLoader(new+URL[]+{new+File("v2.jar").toURL()},+Thread.currentThread().getContextClassLoader());

Class<?>+c1+=+loader1.loadClass("com.abc.Hello");
Class<?>+c2+=+loader2.loadClass("com.abc.Hello");

BaseInterface+i1+=+(BaseInterface)+c1.newInstance();
BaseInterface+i2+=+(BaseInterface)+c2.newInstance();|code-block|syntax|javascript|3080397|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You're going the right way. You must take some things into account.

The normal thing is classes that exist in parent classloaders are used. So if you want two versions those classes must not be there.

But if you want to interact you can use reflection, or even better a common interface. So I'll do this:

<pre><code>common.jar:
BaseInterface

v1.jar:
SomeImplementation implements BaseInterface

v2.jar:
OtherImplementation implements BaseInterface

command-line:
java -classpath common.jar YourMainClass
// you don't put v1 nor v2 into the parent classloader classpath

Then in your program:

loader1 = new URLClassLoader(new URL[] {new File("v1.jar").toURL()}, Thread.currentThread().getContextClassLoader());
loader2 = new URLClassLoader(new URL[] {new File("v2.jar").toURL()}, Thread.currentThread().getContextClassLoader());

Class&lt;?&gt; c1 = loader1.loadClass("com.abc.Hello");
Class&lt;?&gt; c2 = loader2.loadClass("com.abc.Hello");

BaseInterface i1 = (BaseInterface) c1.newInstance();
BaseInterface i2 = (BaseInterface) c2.newInstance();
</code></pre>

blocks|key|218866|text|有关@helios+checkout+github.com/atulsm/ElasticsearchClassLoader接受答案的示例实现，请参阅|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|218867|entityMap|0|LINK|mutability|MUTABLE|url|http://github.com/atulsm/ElasticsearchClassLoader^0|J|16|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

For a sample implementation of the accepted answer by @helios checkout <a href="http://github.com/atulsm/ElasticsearchClassLoader" rel="nofollow">github.com/atulsm/ElasticsearchClassLoader</a>

I have read a lot about Java classloaders, but so far I have failed to find an answer for this simple question:

I have two versions of com.abc.Hello.class in jars v1.jar and v2.jar. I want to use both in my application. What is the simplest way of doing this ?

I don't expect to be that simple, but something along these lines would be awesome :

<pre><code>Classloader myClassLoader = [magic that includes v1.jar and ignores v2.jar]
Hello hello = myclassLoader.load[com.abc.Hello]
</code></pre>

And in a different class :

<pre><code>Classloader myClassLoader = [magic that includes v2.jar and ignores v1.jar]
Hello hello = myclassLoader.load[com.abc.Hello]
</code></pre>

I would like to avoid using OSGi.

Java - how to load different versions of the same class?

Java

我读了很多关于Java类加载器的文章，但到目前为止，我还没有找到这个简单问题的答案：我在jars中有两个版本的com.abc.Hello.class：v1.jar和v2.jar。我想在我的应用程序中同时使用这两种方法。执行此操作的最简单方法是什么？我并不期望这么简单，但以下内容将是非常棒的：Classloader my...

问Java -如何加载同一个类的不同版本？
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