在java spring中，是否可以动态将一个新的class加载到beanFactory中？

Question

在java spring中，是否可以动态将一个新的class加载到beanFactory中？是否可以将class类以字节流的方式存到redis中，再由类加载器重新加载到java运行实例中？
目前项目中有一个需求，需要可以动态地加载类到spring的beanFactory中或者说applicationContext里面，这个类是可以由开发人员动态上传到生产环境中，而无需重新启动生产环境。请问是否可以做到呢？还有一个问题，是否可以将class文件以字节的方式暂存在redis中间件上，需要用这个class时，动态地加载它？

Answer 1

After JDK1.5, there is a ready-made API java.lang.instrument.Instrumentation to implement this function.

java.lang.instrument.Instrumentation.redefineClasses(ClassDefinition... definitions)

The above interface can redefine the existing oneclass.
Use as below.

private void redefineScripts(File dir) {
    File[] files = dir.listFiles();
    for (File f : files) {
        if (f.isDirectory()) {
            redefineScripts(f);
        } else if (f.getName().endsWith(".class")) {
            String name = getScriptCanonicalName(f);
            String path = name.replaceAll("\.", "/");
            File target = new File(targetDir, path + ".class");

            try {
                InputStream in = new FileInputStream(target);
                byte[] buf = StreamUtils.copyToByteArray(in);
                ClassDefinition cdef = new ClassDefinition(scriptClassLoader.loadClass(name), buf);
                instrumentation.redefineClasses(cdef);
            } catch (Exception ex) {
                throw new ScriptException(ex);
            }
        }
    }
}

Method to get Instrumentationobject:

private void loadAgent() {
    try {
        String pid = ManagementFactory.getRuntimeMXBean().getName().split("@")[0];
        VirtualMachine vm = VirtualMachine.attach(pid);
        vm.loadAgent("<jar file>", OBJECT_NAME.toString());
        vm.detach();
    } catch (Exception ex) {
        throw new RuntimeException(
                "无法加载代理JAR文件["
                + Typhons.getProperty(Constants.AGENT_JAR_PATH) + "]", ex);
    }
}

agent.jar打包时需要指定Agent-Class，Can-Redefine-ClassesEnable class rewriting function.

<plugin>
    <artifactId>maven-jar-plugin</artifactId>
    <configuration>
        <archive>
            <manifest>
                <addClasspath>true</addClasspath>
            </manifest>
            <manifestEntries>
                <Agent-Class>org.skfiy.typhon.agent.Agent</Agent-Class>
                <Can-Redefine-Classes>true</Can-Redefine-Classes>
            </manifestEntries>
        </archive>
    </configuration>
</plugin>

Agent.java Realization

public class Agent {

    /**
     * 代理主函数入口. 通过传入的{@code str }{@code ObjectName }执行其{@code setInstrumentation }
     * 方法.
     * <p>
     * e.g.<pre>
     * public void setInstrumentation(Instrumentation instrumentation) {
     *  this.instrumentation = instrumentation;
     * }
     * </pre>
     * 
     * @param str 一个{@link ObjectName }字符串
     * @param inst {@link Instrumentation }实现
     * @throws Exception 异常
     */
    public static void agentmain(String str, Instrumentation inst) throws Exception {
        ObjectName objectName = ObjectName.getInstance(str);
        MBeanServer mbeanServer = MBeanServerFactory.findMBeanServer(null).get(0);
        mbeanServer.invoke(objectName, "setInstrumentation",
                new Object[]{inst},
                new String[]{Instrumentation.class.getName()});
    }
}

Here I injected the JMX将Instrumentation对象注入过去的，当时为什么要这样来做呢。
是因为vm.loadAgent();运行的环境是一个全新的，我无法使用静态方法来设置属性，虽然类相同但是加载该个类的ClassLoader却不一致。后面我尝试出可以使用JMX object through JMX. Why did I do it this way?

It’s because the running environment of vm.loadAgent(); is a brand new one, and I cannot use static methods to set properties. Although the classes are the same, the ClassLoader is inconsistent. Later I tried to call it using JMX.

InstrumentationOkay, as long as you get the

object, you can do anything you couldn't do before. 🎜

Answer 2

Try to get the AutowireCapableBeanFactory through ApplicationContext, and then call the createBean() or autowire() method to inject it

Answer 3

Java has object input and output streams, so you can definitely store objects in bytes

Answer 4

None of what is said above is correct. I can tell you clearly that everything is possible.

Answer 5

mark to learn