java 自定义类加载器 UserDefineClassLoader.java

java 自定义类加载器 UserDefineClassLoader.java

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import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;
 
public class UserDefineClassLoader extends ClassLoader {
    private String classPath;
 
    public UserDefineClassLoader(String classPath) {
        this.classPath = classPath;
    }
 
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        byte[] classData = loadClassData(name);
        return defineClass(name, classData, 0, classData.length);
    }
 
    private byte[] loadClassData(String className) {
        String path = classPath + File.separatorChar + className.replace('.', File.separatorChar) + ".class";
        File file = new File(path);
        FileInputStream fileInputStream = null;
        FileChannel fileChannel = null;
        try {
            fileInputStream = new FileInputStream(file);
            fileChannel = fileInputStream.getChannel();
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            WritableByteChannel writableByteChannel = Channels.newChannel(byteArrayOutputStream);
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            while (fileChannel.read(buffer) != -1) {
                buffer.flip();
                writableByteChannel.write(buffer);
                buffer.clear();
            }
            return byteArrayOutputStream.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (fileChannel != null) {
                    fileChannel.close();
                }
                if (fileInputStream != null) {
                    fileInputStream.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}