How to serialize a runnable? Help me with an error: "NotSerializableException"

Question

Alex_ 0 Junior Poster

13 Years Ago

Hello. I'm trying to serialize a class that implements Serializable and a Runnable. My class has a transient Thread object as a field that is created and started after the restoration of my class(object).

This is proven possibile by a tutorial from Oracle, here. But i fail to compile my program which is very similar to the one in the tutorial(i think).

So in the following i attach my source code and the exception's trace in hope that someone can help me out.

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package ppc2;

import java.io.Serializable;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Main {

    Main(){

        SerializedThread [] threads = new SerializedThread[7];
        for(int i =1 ;i<8;i++){
            if(i==1)
                threads[i] = new SerializedThread(new String[]{"f2","f3","f4"});
            if(i==2)
                threads[i] = new SerializedThread(new String[]{"f5"});
            if(i==3)
                threads[i] = new SerializedThread(new String[]{"f6"});
            if(i==4)
                threads[i] = new SerializedThread(new String[]{"f7"});
        }
        for(int i =0;i<7;i++){
            writeMyObjectToFile(threads[i],"f"+(i+1));
        }
        readMyObjectFromFile("f1");
    }

    private void writeMyObjectToFile(SerializedThread runner, String fileName){
        FileOutputStream fos = null;
        ObjectOutputStream oos = null;
        try{
            fos = new FileOutputStream(fileName);
            oos = new ObjectOutputStream(fos);
            oos.writeObject(runner);
            oos.close();
        }catch(IOException e){
            e.printStackTrace();
        }

    }
    private SerializedThread readMyObjectFromFile(String fileName){
        FileInputStream fis = null;
        ObjectInputStream ois = null;
        SerializedThread runner = null;
        try{
            fis = new FileInputStream(fileName);
            ois = new ObjectInputStream(fis);
            runner = (SerializedThread)ois.readObject();
            ois.close();
        }catch(IOException e){
            e.printStackTrace();
        }catch(ClassNotFoundException ex){
            ex.printStackTrace();
        }
        return runner;
    }

    public static void main(String[] args) {
        new Main();

    }

    class SerializedThread implements Serializable, Runnable {

        transient private SerializedThread[] children = null;
        transient public Thread self = null;
        private String[] childrenFileNames = null;

        SerializedThread(String[] childrenFileNames) {
            setNames(childrenFileNames);
        }

        public void setNames(String[] childrenFileNames) {
            this.childrenFileNames = childrenFileNames;
        }

        @Override
        public void run() {
            restoreGivenChildren();//They will auto start, because of the "start" comand in the readObject function.
        }

        private void restoreGivenChildren() {
            if (childrenFileNames != null) {
                children = new SerializedThread[childrenFileNames.length];
                for (int i = 0; i < childrenFileNames.length; i++) {
                    children[i] = (SerializedThread) readMyObjectFromFile(childrenFileNames[i]);
                    //children[i].self=new Thread(this);
                    children[i].self.start();
                }

            }
        }

//        private void writeObject(ObjectOutputStream out) throws IOException {
//            out.defaultWriteObject();
//        }
//
//        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
//            // our "pseudo-constructor"
//            in.defaultReadObject();
//            // now we are a "live" object again, so let's run rebuild and start
//            self = new Thread(this);
//            self.start();
//        }
    }
}

The error>>>

run:
java.io.NotSerializableException: ppc2.Main
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
        at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
        at ppc2.Main.writeMyObjectToFile(Main.java:42)
        at ppc2.Main.<init>(Main.java:31)
        at ppc2.Main.main(Main.java:67)
java.io.NotSerializableException: ppc2.Main
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
        at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
        at ppc2.Main.writeMyObjectToFile(Main.java:42)
        at ppc2.Main.<init>(Main.java:31)
        at ppc2.Main.main(Main.java:67)
java.io.NotSerializableException: ppc2.Main
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
        at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
        at ppc2.Main.writeMyObjectToFile(Main.java:42)
        at ppc2.Main.<init>(Main.java:31)
        at ppc2.Main.main(Main.java:67)
java.io.NotSerializableException: ppc2.Main
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
        at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
        at ppc2.Main.writeMyObjectToFile(Main.java:42)
        at ppc2.Main.<init>(Main.java:31)
        at ppc2.Main.main(Main.java:67)
BUILD SUCCESSFUL (total time: 0 seconds)

java

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Latest Post 13 Years Ago Latest Post by Alex_

~s.o.s~ 2,560 Failure as a human

13 Years Ago

SerializedThread is an inner class i.e. a class which depends on some outer parent class i.e. there is an association between your class Main and SerializedThread. When you try to serialize SerializedThread, it also tries to serialize Main class (which doesn't implement Serializable) hence the error.

A couple of solutions: make the main class implement Serializable (not recommended) or move the SerializedThread out of Main (recommended).

Alex_ commented: solved +3

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JamesCherrill 4,733 Most Valuable Poster Team Colleague Featured Poster · Answer 1 · 2011-01-04T00:01:28+00:00

Don't have time to cehck this now, but don't you need a default constructor for a Serialisable class to be restored?

Alex_ 0 Junior Poster · Answer 2 · 2011-01-04T00:09:16+00:00

I don't see why, but i added one anyway... and corrected some logic bugs, but the error is the same.
This is my source code now:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package ppc2;

import java.io.Serializable;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Main {

    Main(){

        SerializedThread [] threads = new SerializedThread[7];
        for(int i =1; i < 8; i++) {
            switch (i) {
                case 1:
                    threads[i - 1] = new SerializedThread(new String[]{"f2", "f3", "f4"});
                    break;
                case 2:
                    threads[i - 1] = new SerializedThread(new String[]{"f5"});
                    break;
                case 3:
                    threads[i - 1] = new SerializedThread(new String[]{"f6"});
                    break;
                case 4:
                    threads[i - 1] = new SerializedThread(new String[]{"f7"});
                    break;
                default:
                    threads[i - 1] = new SerializedThread(null);
            }
        }
        for(int i =0;i<7;i++){
            writeMyObjectToFile(threads[i],"f"+(i+1));
        }
        readMyObjectFromFile("f1");
    }

    private void writeMyObjectToFile(SerializedThread runner, String fileName){
        FileOutputStream fos = null;
        ObjectOutputStream oos = null;
        try{
            fos = new FileOutputStream(fileName);
            oos = new ObjectOutputStream(fos);
            oos.writeObject(runner);
            oos.close();
        }catch(IOException e){
            e.printStackTrace();
        }

    }
    private SerializedThread readMyObjectFromFile(String fileName){
        FileInputStream fis = null;
        ObjectInputStream ois = null;
        SerializedThread runner = null;
        try{
            fis = new FileInputStream(fileName);
            ois = new ObjectInputStream(fis);
            runner = (SerializedThread)ois.readObject();
            ois.close();
        }catch(IOException e){
            e.printStackTrace();
        }catch(ClassNotFoundException ex){
            ex.printStackTrace();
        }
        return runner;
    }

    public static void main(String[] args) {
        new Main();

    }

    class SerializedThread implements Serializable, Runnable {

        transient private SerializedThread[] children = null;
        transient public Thread self = null;
        private String[] childrenFileNames = null;

        SerializedThread() {}
        SerializedThread(String[] childrenFileNames) {
            setNames(childrenFileNames);
        }

        public void setNames(String[] childrenFileNames) {
            this.childrenFileNames = childrenFileNames;
        }

        @Override
        public void run() {
            restoreGivenChildren();//They will auto start, because of the "start" comand in the readObject function.
        }

        private void restoreGivenChildren() {
            if (childrenFileNames != null) {
                children = new SerializedThread[childrenFileNames.length];
                for (int i = 0; i < childrenFileNames.length; i++) {
                    children[i] = (SerializedThread) readMyObjectFromFile(childrenFileNames[i]);
                    children[i].self=new Thread(this);
                    children[i].self.start();
                }

            }
        }

//        private void writeObject(ObjectOutputStream out) throws IOException {
//            out.defaultWriteObject();
//        }
//
//        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
//            // our "pseudo-constructor"
//            in.defaultReadObject();
//            // now we are a "live" object again, so let's run rebuild and start
//            self = new Thread(this);
//            self.start();
//        }
    }
}

Me errors>>>

java.io.NotSerializableException: ppc2.Main
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
        at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
        at ppc2.Main.writeMyObjectToFile(Main.java:50)
        at ppc2.Main.<init>(Main.java:39)
        at ppc2.Main.main(Main.java:75)

Alex_ 0 Junior Poster · Answer 3 · 2011-01-04T20:01:39+00:00

Thank you. I separated the classes and the serialization works.