Convert Java object to JSON string using gson

Question

In Java I have object that contains an List of object and each object in List Contains EncryptedInteger object

Vote.java

public class Vote implements Serializable {
private static final long serialVersionUID = 2L;
private int voteId;
private int surveyId;
private int voterId;
private List<Choice> choices;
private boolean counted;


public Vote(){
}

public Vote(int surveyId,int voterId){
    this.surveyId=surveyId;
    this.voterId=voterId;
    this.choices = new ArrayList<Choice>();
    this.counted=false;
}

public Vote(int voteId,int surveyId,int voterId, boolean counted){
    this.voteId=voteId;
    this.surveyId=surveyId;
    this.voterId=voterId;
    this.choices = new ArrayList<Choice>();
    this.counted=counted;
}

public void addChoice(Choice choice) {
    choices.add(choice);
}


public String ChoicesToJson() {
    Gson gson = new Gson();
    String json = gson.toJson(this.choices);
    return json;
}


public void JsonToChoices(String json) {
    Gson gson = new Gson();
    TypeToken<List<Choice>> token = new TypeToken<List<Choice>>() {
    };
    this.choices = gson.fromJson(json, token.getType());
}
public int getVoteId() {
    return voteId;
}
public void setVoteId(int voteId) {
    this.voteId = voteId;
}
public int getSurveyId() {
    return surveyId;
}
public void setSurveyId(int surveyId) {
    this.surveyId = surveyId;
}
public int getVoterId() {
    return voterId;
}
public void setVoterId(int voterId) {
    this.voterId = voterId;
}
public List<Choice> getChoices() {
    return choices;
}
public void setChoices(List<Choice> choices) {
    this.choices = choices;
}
public boolean isCounted() {
    return counted;
}
public void setCounted(boolean counted) {
    this.counted = counted;
}}

Choice.java

 public class Choice implements Serializable {

    private static final long serialVersionUID = 3L;
    private EncryptedInteger encryptedInteger;
    private int questionNumber;
    private int optionNumber;
    private double S;

    public Choice(EncryptedInteger encryptedInteger, int questionNumber,
            int optionNumber, double s) {

        this.encryptedInteger = encryptedInteger;
        this.questionNumber = questionNumber;
        this.optionNumber = optionNumber;
        S = s;
    }

    public EncryptedInteger getEncryptedInteger() {
        return encryptedInteger;
    }

    public void setEncryptedInteger(EncryptedInteger encryptedInteger) {
        this.encryptedInteger = encryptedInteger;
    }

    public int getQuestionNumber() {
        return questionNumber;
    }

    public void setQuestionNumber(int questionNumber) {
        this.questionNumber = questionNumber;
    }

    public int getOptionNumber() {
        return optionNumber;
    }

    public void setOptionNumber(int optionNumber) {
        this.optionNumber = optionNumber;
    }

    public double getS() {
        return S;
    }

    public void setS(double s) {
        S = s;
    }

    public String encryptedtoJson() {
        Gson gson = new Gson();

        String json = gson.toJson(this.encryptedInteger);

        return json;

    }}

I am using this EncryptedInteger

When I want to convert the object to Json using Gson it show this error

java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: java.math.BigInteger. Forgot to register a type adapter?
    com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:67)
    com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:61)
    com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    com.google.gson.Gson.toJson(Gson.java:593)
    com.google.gson.Gson.toJson(Gson.java:572)
    com.google.gson.Gson.toJson(Gson.java:527)
    recieving.request.server.GenerateNumberRequest.GNA(GenerateNumberRequest.java:151)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:606)
    com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
    com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:185)
    com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
    com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302)
    com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
    com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
    com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1511)
    com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1442)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1391)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1381)
    com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:538)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:716)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

Another example that show the same error :

public class test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        PrivateKey prk=new PrivateKey(1024);
        PublicKey pup= prk.getPublicKey();

        try {
            EncryptedInteger e=new EncryptedInteger(BigInteger.ONE, pup);
            Gson gson=new Gson();
System.out.println(gson.toJson(e));
  } catch (BigIntegerClassNotValid e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

Can you help me specifying the error and how to solve it ?

Note: I doubled check I am Using Gson 2.2.4

Answer 1

The version of EncryptedInteger you link to isn't the one you're using.

The one you're using is this one (The current version).

The difference is that it includes this line:

private Class bigi;

And it assigns BigInteger.class to it.

Gson can't serialize that, and that's what is throwing that exception.

You're going to have to write a custom serializer / deserializer to handle that class. The section for this in the Gson user guide should get you started. There's also numerous questions/answers on SO covering the subject.

Edit from comments:

I didn't look at it much further. Looking at it now, I mean, it uses that for something. It also holds an instance of java.util.Random.

Looking at it a little more in-depth ... you kind of have a problem serializing/deserializing it the way it sits. There's no constructor or public method to set the encrypted value. The method that would be useful for that is private (setCipherVal()). If that were public you could just write a serializer that outputs JSON holding the PublicKey and the encrypted value, then in your deserializer use those to create a new EncryptedInteger.

Without changing that class to allow for that I don't see a way to serialize/deserialize it to JSON.

Last edit: Actually, you could, it's just ugly because you have to use reflection to set the cipherval directly after constructing the EncryptedInteger with just the PublicKey