Java 如何在运行时动态加载JAR文件?
为什么在Java中这么难做到这一点?如果您想拥有任何类型的模块系统,您需要能够动态加载JAR文件。有人告诉我,有一种方法可以通过编写自己的Java 如何在运行时动态加载JAR文件?,java,jar,classloader,Java,Jar,Classloader,为什么在Java中这么难做到这一点?如果您想拥有任何类型的模块系统,您需要能够动态加载JAR文件。有人告诉我,有一种方法可以通过编写自己的类加载器来实现这一点,但这需要做大量的工作,至少在我看来,这应该像使用JAR文件作为参数调用方法一样简单 对实现这一点的简单代码有什么建议吗?下面的解决方案很粗糙,因为它使用反射来绕过封装,但它工作得非常完美: File file = ... URL url = file.toURI().toURL(); URLClassLoader classLoader
类加载器来实现这一点,但这需要做大量的工作,至少在我看来,这应该像使用JAR文件作为参数调用方法一样简单
对实现这一点的简单代码有什么建议吗?下面的解决方案很粗糙,因为它使用反射来绕过封装,但它工作得非常完美:
File file = ...
URL url = file.toURI().toURL();
URLClassLoader classLoader = (URLClassLoader)ClassLoader.getSystemClassLoader();
Method method = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);
method.setAccessible(true);
method.invoke(classLoader, url);
您应该查看,例如,在中实现的。正是这样。您可以安装、卸载、启动和停止所谓的bundle,它们实际上是JAR文件。但它做得更多,因为它提供了一些服务,例如,可以在运行时在JAR文件中动态发现这些服务
或者参见规范。它之所以难是因为安全性。类加载器是不可变的;您不应该在运行时随意向它添加类。事实上,我非常惊讶它能与系统类加载器一起工作。下面是制作自己的子类加载器的方法:
URLClassLoader child = new URLClassLoader(
new URL[] {myJar.toURI().toURL()},
this.getClass().getClassLoader()
);
Class classToLoad = Class.forName("com.MyClass", true, child);
Method method = classToLoad.getDeclaredMethod("myMethod");
Object instance = classToLoad.newInstance();
Object result = method.invoke(instance);
很痛苦,但确实如此。我发现最好的办法就是把它作为项目的一部分
这是我过去使用过的一个简短方法,用于从特定目录中的所有lib文件创建类加载器
public void initialize(String libDir) throws Exception {
File dependencyDirectory = new File(libDir);
File[] files = dependencyDirectory.listFiles();
ArrayList<URL> urls = new ArrayList<URL>();
for (int i = 0; i < files.length; i++) {
if (files[i].getName().endsWith(".jar")) {
urls.add(files[i].toURL());
//urls.add(files[i].toURI().toURL());
}
}
classLoader = new JarFileClassLoader("Scheduler CL" + System.currentTimeMillis(),
urls.toArray(new URL[urls.size()]),
GFClassLoader.class.getClassLoader());
}
这辆车怎么样?我得承认,我没有用过,但它看起来很有前途
用法示例:
JarClassLoader jcl = new JarClassLoader();
jcl.add("myjar.jar"); // Load jar file
jcl.add(new URL("http://myserver.com/myjar.jar")); // Load jar from a URL
jcl.add(new FileInputStream("myotherjar.jar")); // Load jar file from stream
jcl.add("myclassfolder/"); // Load class folder
jcl.add("myjarlib/"); // Recursively load all jar files in the folder/sub-folder(s)
JclObjectFactory factory = JclObjectFactory.getInstance();
// Create object of loaded class
Object obj = factory.create(jcl, "mypackage.MyClass");
这是一个未弃用的版本。我修改了原始版本以删除不推荐使用的功能
/**************************************************************************************************
* 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();
}
}
/**************************************************************************************************
* Copyright(C)2004,联邦大学的SO卡洛斯*
* *
*版权所有*
* *
*允许以源代码和二进制形式重新分发和使用,无论是否修改*
*但须符合下列条件:*
* *
**源代码的重新分发必须保留上述版权声明,此列表*
*条件和以下免责声明*
**以二进制形式重新分发时,必须复制上述版权声明,即*
**文件和/或其他材料中的条件和以下免责声明*
**提供分配*
*既不是卡洛斯大学的名字,也不是它的名字。
**贡献者可用于支持或推广从本软件衍生的产品*
**未经事先书面许可*
* *
*本软件由版权所有者和贡献者提供*
*“原样”和任何明示或暗示的保证,包括但不限于*
*仅限于对适销性和适用性的默示保证*
*不承认有特定目的。在任何情况下,版权所有人或*
*出资人对任何直接、间接、附带、特殊、*
*惩戒性或间接损害(包括但不限于*
*替代货物或服务的采购;使用、数据或服务的损失*
*利润;或业务中断),无论是何种原因造成的*
*责任,无论是合同责任、严格责任还是侵权责任(包括*
*因使用本文件而产生的任何疏忽或其他原因)*
*软件,即使已告知此类损坏的可能性*
**************************************************************************************************/
/*
*创建于2004年10月6日
*/
成套工具;
导入java.io.File;
导入java.io.IOException;
导入java.lang.reflect.Constructor;
导入java.lang.reflect.InvocationTargetException;
导入java.lang.reflect.Method;
导入java.net.URL;
导入java.net.URLClassLoader;
/**
*用于动态更改类路径、在运行时添加类的有用类。
*/
公共类路径黑客{
/**
*将URL添加到系统类的方法的参数。
*/
私有静态最终类[]参数=新类[]{URL.Class};
/**
*将文件添加到类路径。
*@param是指向文件的字符串
*@抛出异常
*/
公共静态void addFile(字符串s)引发IOException{
文件f=新文件;
addFile(f);
}
/**
*将文件添加到类路径
*@param f要添加的文件
*@抛出异常
*/
公共静态void addFile(文件f)引发IOException{
addURL(f.toURI().toul());
}
/**
*将URL指向的内容添加到类路径。
*@param u指向要添加的内容的URL
*@抛出异常
*/
公共静态void addURL(URL u)引发IOException{
URLClassLoader sysloader=(URLClassLoader)ClassLoader.getSystemClassLoader();
类sysclass=URLClassLoader.Class;
试一试{
Method=sysclass.getDeclaredMethod(“addURL”,参数);
M
/**************************************************************************************************
* 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();
}
}
String jarFile = "path/to/jarfile.jar";
DexClassLoader classLoader = new DexClassLoader(jarFile, "/data/data/" + context.getPackageName() + "/", null, getClass().getClassLoader());
Class<?> myClass = classLoader.loadClass("MyClass");
Thread.currentThread().setContextClassLoader(classLoader);
java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader
package ClassPathAgent;
import java.io.IOException;
import java.lang.instrument.Instrumentation;
import java.util.jar.JarFile;
public class ClassPathAgent {
public static void agentmain(String args, Instrumentation instrumentation) throws IOException {
instrumentation.appendToSystemClassLoaderSearch(new JarFile(args));
}
}
Manifest-Version: 1.0
Agent-Class: ClassPathAgent.ClassPathAgent
import java.io.File;
import net.bytebuddy.agent.ByteBuddyAgent;
public class ClassPathUtil {
private static File AGENT_JAR = new File("/path/to/agent.jar");
public static void addJarToClassPath(File jarFile) {
ByteBuddyAgent.attach(AGENT_JAR, String.valueOf(ProcessHandle.current().pid()), jarFile.getPath());
}
}
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();
File file = ...
URL url = file.toURI().toURL();
URLClassLoader sysLoader = new URLClassLoader(new URL[0]);
Method sysMethod = URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{URL.class});
sysMethod.setAccessible(true);
sysMethod.invoke(sysLoader, new Object[]{url});
package agent;
import java.io.IOException;
import java.lang.instrument.Instrumentation;
import java.util.jar.JarFile;
public class Agent {
public static Instrumentation instrumentation;
public static void premain(String args, Instrumentation instrumentation) {
Agent.instrumentation = instrumentation;
}
public static void agentmain(String args, Instrumentation instrumentation) {
Agent.instrumentation = instrumentation;
}
public static void appendJarFile(JarFile file) throws IOException {
if (instrumentation != null) {
instrumentation.appendToSystemClassLoaderSearch(file);
}
}
}
Launcher-Agent-Class: agent.Agent
Agent-Class: agent.Agent
Premain-Class: agent.Agent
java -jar <your jar>
java -javaagent:<your jar> -jar <your jar>
Agent.appendJarFile(new JarFile(<your file>));
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
ClassLoader classLoader = ClassLoader.getSystemClassLoader();
try {
Method method = classLoader.getClass().getDeclaredMethod("addURL", URL.class);
method.setAccessible(true);
method.invoke(classLoader, new File(jarPath).toURI().toURL());
} catch (NoSuchMethodException e) {
Method method = classLoader.getClass()
.getDeclaredMethod("appendToClassPathForInstrumentation", String.class);
method.setAccessible(true);
method.invoke(classLoader, jarPath);
}
java -Djava.system.class.loader=com.example.MyCustomClassLoader
public static synchronized void loadLibrary(java.io.File jar) {
try {
java.net.URL url = jar.toURI().toURL();
java.lang.reflect.Method method = java.net.URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{java.net.URL.class});
method.setAccessible(true); /*promote the method to public access*/
method.invoke(Thread.currentThread().getContextClassLoader(), new Object[]{url});
} catch (Exception ex) {
throw new RuntimeException("Cannot load library from jar file '" + jar.getAbsolutePath() + "'. Reason: " + ex.getMessage());
}
}
File object = new File(pack.getObjectFile()).getAbsoluteFile();
Object packObject;
try {
URLClassLoader classloader;
List<URL> classpath = new ArrayList<>();
classpath.add(new File(pack.getObjectRootPath()).toURI().toURL());
for (File jar : FileUtils.listFiles(new File(pack.getLibPath()), new String[] {"jar"}, true)) {
classpath.add(jar.toURI().toURL());
}
classloader = new URLClassLoader(classpath.toArray(new URL[] {}));
Class<?> clazz = classloader.loadClass(object.getName());
packObject = clazz.getDeclaredConstructor().newInstance();
} catch (Exception e) {
e.printStackTrace();
throw e;
}
return packObject;
public interface Greeting extends ExtensionPoint {
String getGreeting();
}
@Extension
public class WelcomeGreeting implements Greeting {
public String getGreeting() {
return "Welcome";
}
}
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();
}