用不同的软件包名称在Java中的动态加载类

Question

是否可以在Java中加载类并“伪造”类的包装名称/规范名称？我尝试这样做，这是一种显而易见的方法，但是我在 ClassDefNotFoundException.

我这样做的原因是我正在尝试加载默认软件包中写入的API，以便我可以直接使用它而无需使用反射。该代码将以代表软件包和软件包名称导入的文件夹结构中的类编译。 IE：

./com/DefaultPackageClass.class

// ...
import com.DefaultPackageClass;
import java.util.Vector;
// ...

我当前的代码如下：

public Class loadClass(String name) throws ClassNotFoundException {
    if(!CLASS_NAME.equals(name))
            return super.loadClass(name);

    try {
        URL myUrl = new URL(fileUrl);
        URLConnection connection = myUrl.openConnection();
        InputStream input = connection.getInputStream();
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        int data = input.read();

        while(data != -1){
            buffer.write(data);
            data = input.read();
        }

        input.close();

        byte[] classData = buffer.toByteArray();

        return defineClass(CLASS_NAME,
                classData, 0, classData.length);

    } catch (MalformedURLException e) {
        throw new UndeclaredThrowableException(e);
    } catch (IOException e) {
        throw new UndeclaredThrowableException(e); 
    }

}

Answer 1

正如皮特提到的那样, ，可以使用ASM字节码库来完成。实际上，该图书馆实际上是使用专门处理这些类名称重新构图的课程（RemappingClassAdapter）。这是使用此类的类加载程序的示例：

public class MagicClassLoader extends ClassLoader {

    private final String defaultPackageName;

    public MagicClassLoader(String defaultPackageName) {
        super();
        this.defaultPackageName = defaultPackageName;
    }

    public MagicClassLoader(String defaultPackageName, ClassLoader parent) {
        super(parent);
        this.defaultPackageName = defaultPackageName;
    }

    @Override
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        byte[] bytecode = ...; // I will leave this part up to you
        byte[] remappedBytecode;

        try {
            remappedBytecode = rewriteDefaultPackageClassNames(bytecode);
        } catch (IOException e) {
            throw new RuntimeException("Could not rewrite class " + name);
        }

        return defineClass(name, remappedBytecode, 0, remappedBytecode.length);
    }

    public byte[] rewriteDefaultPackageClassNames(byte[] bytecode) throws IOException {
        ClassReader classReader = new ClassReader(bytecode);
        ClassWriter classWriter = new ClassWriter(classReader, 0);

        Remapper remapper = new DefaultPackageClassNameRemapper();
        classReader.accept(
                new RemappingClassAdapter(classWriter, remapper),
                0
            );

        return classWriter.toByteArray();
    }

    class DefaultPackageClassNameRemapper extends Remapper {

        @Override
        public String map(String typeName) {
            boolean hasPackageName = typeName.indexOf('.') != -1;
            if (hasPackageName) {
                return typeName;
            } else {
                return defaultPackageName + "." + typeName;
            }
        }

    }

}

为了说明，我创建了两个类，这两个类都属于默认软件包：

public class Customer {

}

和

public class Order {

    private Customer customer;

    public Order(Customer customer) {
        this.customer = customer;
    }

    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

}

这是 Order 前 重新映射：

> javap -private -c Order
Compiled from "Order.java"
public class Order extends java.lang.Object{
private Customer customer;

public Order(Customer);
  Code:
   0:   aload_0
   1:   invokespecial   #10; //Method java/lang/Object."":()V
   4:   aload_0
   5:   aload_1
   6:   putfield    #13; //Field customer:LCustomer;
   9:   return

public Customer getCustomer();
  Code:
   0:   aload_0
   1:   getfield    #13; //Field customer:LCustomer;
   4:   areturn

public void setCustomer(Customer);
  Code:
   0:   aload_0
   1:   aload_1
   2:   putfield    #13; //Field customer:LCustomer;
   5:   return

}

这是 Order 后 重新映射（使用 com.mycompany 作为默认软件包）：

> javap -private -c Order
Compiled from "Order.java"
public class com.mycompany.Order extends com.mycompany.java.lang.Object{
private com.mycompany.Customer customer;

public com.mycompany.Order(com.mycompany.Customer);
  Code:
   0:   aload_0
   1:   invokespecial   #30; //Method "com.mycompany.java/lang/Object"."":()V
   4:   aload_0
   5:   aload_1
   6:   putfield    #32; //Field customer:Lcom.mycompany.Customer;
   9:   return

public com.mycompany.Customer getCustomer();
  Code:
   0:   aload_0
   1:   getfield    #32; //Field customer:Lcom.mycompany.Customer;
   4:   areturn

public void setCustomer(com.mycompany.Customer);
  Code:
   0:   aload_0
   1:   aload_1
   2:   putfield    #32; //Field customer:Lcom.mycompany.Customer;
   5:   return

}

如您所见，重新映射已经改变了所有 Order 参考 com.mycompany.Order 和所有 Customer 参考 com.mycompany.Customer.

此类加载程序必须加载所有的所有类：

• 属于默认包，或
• 使用属于默认软件包的其他类。

Answer 2

你应该能够敲一些东西 ASM, ，尽管在构建时间而不是在加载时间上进行一次重命名的软件包会更容易。

Answer 3

也许将API从默认软件包移动到更合理的位置会更容易？听起来您无法访问源代码。我不确定该软件包是否已编码为类文件，因此仅移动API类可能值得一试。否则，像JAD这样的Java分解器通常会做得很好，因此您可以更改分配源中的包装名称并再次编译。