这可能是一个延迟响应，我可以这样做(fastutil-8.2.2.jar的一个简单示例)使用jhplot。来自DataMelt的Web类(http://jwork.org/dmelt)

import jhplot.Web;
Web.load("http://central.maven.org/maven2/it/unimi/dsi/fastutil/8.2.2/fastutil-8.2.2.jar"); // now you can start using this library

根据文档，这个文件将在“lib/user”中下载，然后动态加载，因此您可以立即在同一个程序中使用这个jar文件中的类。

我知道我来晚了，但我一直在使用pf4j，这是一个插件框架，它工作得非常好。

PF4J是一个微框架，其目标是保持核心简单但可扩展。

一个插件使用的例子:

在你的应用/插件中使用ExtensionPoint接口标记定义一个扩展点:

public interface Greeting extends ExtensionPoint {

    String getGreeting();

}

使用@Extension注释创建一个扩展:

@Extension
public class WelcomeGreeting implements Greeting {

    public String getGreeting() {
        return "Welcome";
    }

}

然后你可以加载和卸载插件，如你所愿:

public static void main(String[] args) {

    // create the plugin manager
    PluginManager pluginManager = new JarPluginManager(); // or "new ZipPluginManager() / new DefaultPluginManager()"

    // start and load all plugins of application
    pluginManager.loadPlugins();
    pluginManager.startPlugins();

    // retrieve all extensions for "Greeting" extension point
    List<Greeting> greetings = pluginManager.getExtensions(Greeting.class);
    for (Greeting greeting : greetings) {
        System.out.println(">>> " + greeting.getGreeting());
    }

    // stop and unload all plugins
    pluginManager.stopPlugins();
    pluginManager.unloadPlugins();

}

欲了解更多细节，请参阅文档

请看看我开始的这个项目:proxy-object lib

这个库将从文件系统或任何其他位置加载jar。它将为jar专用一个类装入器，以确保没有库冲突。用户将能够从加载的jar中创建任何对象，并在其上调用任何方法。 这个库被设计用来从支持Java 7的代码库中加载用Java 8编译的jar。

创建一个对象:

    File libDir = new File("path/to/jar");

    ProxyCallerInterface caller = ObjectBuilder.builder()
            .setClassName("net.proxy.lib.test.LibClass")
            .setArtifact(DirArtifact.builder()
                    .withClazz(ObjectBuilderTest.class)
                    .withVersionInfo(newVersionInfo(libDir))
                    .build())
            .build();
    String version = caller.call("getLibVersion").asString();

ObjectBuilder支持工厂方法、调用静态函数和回调接口实现。 我将在自述页面上发布更多的例子。

下面是一个未弃用的版本。我修改了原始版本，删除了不推荐使用的功能。

/**************************************************************************************************
 * Copyright (c) 2004, Federal University of So Carlos                                           *
 *                                                                                                *
 * All rights reserved.                                                                           *
 *                                                                                                *
 * Redistribution and use in source and binary forms, with or without modification, are permitted *
 * provided that the following conditions are met:                                                *
 *                                                                                                *
 *     * Redistributions of source code must retain the above copyright notice, this list of      *
 *       conditions and the following disclaimer.                                                 *
 *     * Redistributions in binary form must reproduce the above copyright notice, this list of   *
 *     * conditions and the following disclaimer in the documentation and/or other materials      *
 *     * provided with the distribution.                                                          *
 *     * Neither the name of the Federal University of So Carlos nor the names of its            *
 *     * contributors may be used to endorse or promote products derived from this software       *
 *     * without specific prior written permission.                                               *
 *                                                                                                *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS                            *
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT                              *
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR                          *
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR                  *
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,                          *
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,                            *
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR                             *
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF                         *
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING                           *
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS                             *
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.                                   *
 **************************************************************************************************/
/*
 * Created on Oct 6, 2004
 */
package tools;

import java.io.File;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

/**
 * Useful class for dynamically changing the classpath, adding classes during runtime. 
 */
public class ClasspathHacker {
    /**
     * Parameters of the method to add an URL to the System classes. 
     */
    private static final Class<?>[] parameters = new Class[]{URL.class};

    /**
     * Adds a file to the classpath.
     * @param s a String pointing to the file
     * @throws IOException
     */
    public static void addFile(String s) throws IOException {
        File f = new File(s);
        addFile(f);
    }

    /**
     * Adds a file to the classpath
     * @param f the file to be added
     * @throws IOException
     */
    public static void addFile(File f) throws IOException {
        addURL(f.toURI().toURL());
    }

    /**
     * Adds the content pointed by the URL to the classpath.
     * @param u the URL pointing to the content to be added
     * @throws IOException
     */
    public static void addURL(URL u) throws IOException {
        URLClassLoader sysloader = (URLClassLoader)ClassLoader.getSystemClassLoader();
        Class<?> sysclass = URLClassLoader.class;
        try {
            Method method = sysclass.getDeclaredMethod("addURL",parameters);
            method.setAccessible(true);
            method.invoke(sysloader,new Object[]{ u }); 
        } catch (Throwable t) {
            t.printStackTrace();
            throw new IOException("Error, could not add URL to system classloader");
        }        
    }

    public static void main(String args[]) throws IOException, SecurityException, ClassNotFoundException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException{
        addFile("C:\\dynamicloading.jar");
        Constructor<?> cs = ClassLoader.getSystemClassLoader().loadClass("test.DymamicLoadingTest").getConstructor(String.class);
        DymamicLoadingTest instance = (DymamicLoadingTest)cs.newInstance();
        instance.test();
    }
}

对于jar文件的动态上传，您可以使用我对URLClassLoader的修改。这种修改对于在应用程序操作期间更改jar文件没有问题，就像标准的URLClassloader一样。所有加载的jar文件都加载到RAM中，因此独立于原始文件。

内存中的jar和JDBC类装入器

这可能是一个延迟响应，我可以这样做(fastutil-8.2.2.jar的一个简单示例)使用jhplot。来自DataMelt的Web类(http://jwork.org/dmelt)

import jhplot.Web;
Web.load("http://central.maven.org/maven2/it/unimi/dsi/fastutil/8.2.2/fastutil-8.2.2.jar"); // now you can start using this library

根据文档，这个文件将在“lib/user”中下载，然后动态加载，因此您可以立即在同一个程序中使用这个jar文件中的类。