使用gson将Java对象转换为JSON字符串

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