java - 类加载器 : how to load class from another project

Question

我想使用 ClassLoader 从另一个项目访问一个类。如何指定该类的路径并获取该类文件？

我希望能够通过代码完成此操作，因为我将通过我的应用程序加载许多不同的类文件，并且不同类的路径将不断变化。

我正在使用 CustomClassLoader，它正在加载类文件，但前提是它们在项目中而不是在另一个项目中

import java.io.FileInputStream;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedExceptionAction;

public class CustomClassLoader extends ClassLoader {

String repoLocation = "C:/TempBINfolder/bin/";

public CustomClassLoader() {
}

public CustomClassLoader(ClassLoader parent) {
    super(parent);
}

@Override
protected Class<?> findClass(final String name)
        throws ClassNotFoundException {

    AccessControlContext acc = AccessController.getContext();

    try {
        return (Class) AccessController.doPrivileged(
                new PrivilegedExceptionAction() {

                    public Object run() throws ClassNotFoundException {

                        FileInputStream fi = null;
                        try {

                            String path = name.replace('.', '/');
                            fi = new FileInputStream(repoLocation + path
                                    + ".class");
                            ByteArrayOutputStream baos = new ByteArrayOutputStream();
                            byte[] buffer = new byte[8192]; // a big chunk
                            int read;
                            while ((read = fi.read(buffer)) > 0)
                                baos.write(buffer, 0, read);
                            byte[] classBytes= baos.toByteArray();

                            return defineClass(name, classBytes, 0,
                                    classBytes.length);
                        } catch (Exception e) {
                            throw new ClassNotFoundException(name);
                        }
                    }
                }, acc);
    } catch (java.security.PrivilegedActionException pae) {
        return super.findClass(name);
    }
}
}

调用类

for (Class singleClass : listOfClasses) {
            try {

                ClassLoader classLoader = new CustomClassLoader(ClassLoader.getSystemClassLoader());
                Class stringClass = null;
                try {
                    stringClass = classLoader.loadClass(singleClass.getName());
                } catch (ClassNotFoundException ex) {
                    Logger.getLogger(CompilerForm.class.getName()).log(Level.SEVERE, null, ex);
                }
                try {
                    stringClass.newInstance();
                } catch (InstantiationException ex) {
                    Logger.getLogger(CompilerForm.class.getName()).log(Level.SEVERE, null, ex);
                } catch (IllegalAccessException ex) {
                    Logger.getLogger(CompilerForm.class.getName()).log(Level.SEVERE, null, ex);
                }


                Class cls = Class.forName(stringClass.getName());

如果我尝试执行 Class cls = Class.forName(stringClass.getPackage()+"."+stringClass.getName()); 包为 null

编辑:以下对我有用

URL classUrl;
classUrl = new URL("file:///"+ccl.getRepoLocation());    //This is location of .class file
URL[] classUrls = {classUrl};
URLClassLoader ucl = new URLClassLoader(classUrls);
Class cls = ucl.loadClass(stringClass.getName());    // Current .class files name

Answer 1

使用 URLClassLoader为你做到这一点。