实际上有一个可以使用的技巧

Actually there is a trick that could be used

最初，当您致电

classLoader.defineClass(className, classBytes, 0, classBytes.length)

它会调用Java本机方法 defineClass1 ，该方法实际上会调用 loadClass 方法.

It calls java native method defineClass1 that actually calls loadClass method.

因此，可以拦截此方法并对其进行处理，使其与原始方法有所不同.

So, possible to intercept this method and process it a bit different then original.

在包含缓存的类文件的文件夹中，我将以下常规代码编译为类: A.class

In the folder that contains cached class files I have the following groovy compiled to class: A.class

println "Hello World!"

B.class 检查相关类的加载情况

B.class to check dependent class loading

class B extends A {
    def run(){
        super.run()
        println "Hello from ${this.getClass()}!"
    }
}

和 C.class 检查多级类的加载情况

and C.class to check multi-level class loading

我使用此 jar 来编译以下类，运行类重新加载示例

i used this jar to compile following class and run the class re-loading example

class C extends org.apache.commons.lang3.RandomUtils {
    def rnd(){ nextInt() }
}

以下类+代码加载并重新加载同一类:

the following class + code loads and reloads the same class:

import java.security.PrivilegedAction;
import java.security.AccessController;
import org.codehaus.groovy.control.CompilationFailedException;

@groovy.transform.CompileStatic
class CacheClassLoader extends GroovyClassLoader{
    private File cacheDir = new File('/11/tmp/a__cache')

    private CacheClassLoader(){throw new RuntimeException("default constructor not allowed")}

    public CacheClassLoader(ClassLoader parent){
        super(parent)
    }
    public CacheClassLoader(Script parent){
        this(parent.getClass().getClassLoader())
    }

    @Override
    protected Class getClassCacheEntry(String name) {
        Class clazz = super.getClassCacheEntry(name)
        if( clazz ){
            println "getClassCacheEntry $name -> got from memory cache"
            return clazz
        }
        def cacheFile = new File(cacheDir, name.tr('.','/')+'.class')
        if( cacheFile.exists() ){
            println "getClassCacheEntry $name -> cache file exists, try to load it"
            //clazz = getPrivelegedLoader().defineClass(name, cacheFile.bytes)
            clazz = getPrivelegedLoader().defineClass(name, cacheFile.bytes)
            super.setClassCacheEntry(clazz)
        }
        return clazz
    }

    private PrivelegedLoader getPrivelegedLoader(){
        PrivelegedLoader loader = AccessController.doPrivileged(new PrivilegedAction<PrivelegedLoader>() {
            public PrivelegedLoader run() {
                return new PrivelegedLoader();
            }
        });
    }
    public class PrivelegedLoader extends CacheClassLoader {
        private final CacheClassLoader delegate

        public PrivelegedLoader(){ 
            super(CacheClassLoader.this)
            this.delegate = CacheClassLoader.this
        }

        public Class loadClass(String name, boolean lookupScriptFiles, boolean preferClassOverScript, boolean resolve) throws ClassNotFoundException, CompilationFailedException {
            Class c = findLoadedClass(name);
            if (c != null) return c;
            return delegate.loadClass(name, lookupScriptFiles, preferClassOverScript, resolve);
        }
    }
}

def c=null
//just to show intermediate class loaders could load some classes that will be used in CacheClassLoader
def cl_0 = new GroovyClassLoader(this.getClass().getClassLoader())
cl_0.addClasspath('/11/tmp/a__cache/commons-lang3-3.5.jar')
//create cache class loader
def cl = new CacheClassLoader(cl_0)

println "---1---"
c = cl.loadClass('A')
c.newInstance().run()

println "---2---"
c = cl.loadClass('A')
c.newInstance().run()

println "---3---"
cl.removeClassCacheEntry('A')
c = cl.loadClass('A')
c.newInstance().run()

println "---4---"
c = cl.loadClass('B')
c.newInstance().run()

println "---5---"
cl.removeClassCacheEntry('A')
cl.removeClassCacheEntry('B')
c = cl.loadClass('B')
c.newInstance().run()

println "---6---"
c = cl.loadClass('C')
println c.newInstance().rnd()

结果:

---1---
getClassCacheEntry A -> cache file exists, try to load it
Hello World!
---2---
getClassCacheEntry A -> got from memory cache
Hello World!
---3---
getClassCacheEntry A -> cache file exists, try to load it
Hello World!
---4---
getClassCacheEntry B -> cache file exists, try to load it
getClassCacheEntry A -> got from memory cache
Hello World!
Hello from class B!
---5---
getClassCacheEntry B -> cache file exists, try to load it
getClassCacheEntry A -> cache file exists, try to load it
Hello World!
Hello from class B!
---6---
getClassCacheEntry C -> cache file exists, try to load it
226399895

PS:不确定是否需要特权访问

PS: not sure priviledged access required