Unable to deserialize MultivaluedHashMap<String, String> in Java

Question

I'm trying to deserialize a javax.ws.rs.core.MultivaluedHashMap.

The MultivaluedHashMap implements java.io.Serializable and has a public, no arg constructor.

However when deserializing a previously serialized MultivaluedHashMap, an InvalidClassException, no valid constructor, is thrown:

Exception in thread "main" org.apache.commons.lang3.SerializationException: java.io.InvalidClassException: javax.ws.rs.core.MultivaluedHashMap; no valid constructor at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:231) at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:267) at org.arx.serializationtest.Main.main(Main.java:17) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144) Caused by: java.io.InvalidClassException: javax.ws.rs.core.MultivaluedHashMap; no valid constructor at java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(ObjectStreamClass.java:150) at java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:768) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1775) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351) at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1993) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1918) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351) at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371) at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:223) ... 7 more

This is easily reproduced by running the simple 3 lines long main method below:

package test;

import org.apache.commons.lang3.SerializationUtils;
import javax.ws.rs.core.MultivaluedHashMap;

public class Test {
    public static void main(String[] args) throws Exception {

        MultivaluedHashMap<String, String> map = new MultivaluedHashMap<String, String>();
        byte[] serializedMap = SerializationUtils.serialize(map);

        MultivaluedHashMap<String, String> deserializedMap = SerializationUtils.deserialize(serializedMap);
    }
}

From there I'm not sure how to fix this issue. Any suggestion or pointer would be very much appreciated.

Thanks in advance for your help.

Answer 1

It seems that one of the classes that is needed for deserializeing MultivaluedHashMap doesn't have a parameterless constructor. You can do something like this:

MultivaluedHashMap<String, String> map = new MultivaluedHashMap<String, String>();
HashMap<String, List<String>> serMap = new HashMap<String, List<String>>(map);
byte[] serializedMap = SerializationUtils.serialize(serMap);

HashMap<String, List<String>> tempMap = SerializationUtils.deserialize(serializedMap);
MultivaluedHashMap<String, String> deserializedMap = new MultivaluedHashMap<String, String>();
for (Entry<String, List<String>> entry : tempMap.entrySet()) {
    deserializedMap.put(entry.getKey(), entry.getValue());
}

What this does is to create a HashMap which will hold all the values needed to reconstruct the original MultivaluedHashMap and serialize/deserialize this HashMap instead of the MultivaluedHashMap.

Answer 2

This happened because MultivaluedHashMap does not implement Serializable. To solve this do the following:

import java.io.Serializable;

import javax.ws.rs.core.MultivaluedHashMap;

public class MyMultivaluedHashMap<K, V> extends MultivaluedHashMap<K, V> implements Serializable{
	private static final long	serialVersionUID	= 1L;
	public MyMultivaluedHashMap(){
		super();
		//there are other contruc super class
	}
}

//your code
import javax.ws.rs.core.MultivaluedHashMap;

import org.apache.commons.lang3.SerializationUtils;

public class Teste{
    public Teste(){}
    public static void main(String[] args) throws Exception{
        MyMultivaluedHashMap<String, String> map = new MyMultivaluedHashMap<String, String>();
        map.addFirst("key-1", "chubby");
        map.add("key-2", "skinny");
        byte[] serializedMap = SerializationUtils.serialize(map);
        System.out.println(serializedMap);
        MultivaluedHashMap<String, String> deserializedMap = SerializationUtils.deserialize(serializedMap);
        System.out.println(deserializedMap);
    }
}

So you just create a new class, MyMultivaluedHashMap, that implements Serializable.