Jackson JsonMappingException: Can not deserialize instance

Question

I'm trying to convert my json data to a POJO object using Jackson. Here is the MainActivity and my POJO class code. I'm basically getting a JsonMappingException error. I have also attached the whole log.

MainActivity.java :

ObjectMapper mapper = new ObjectMapper();
    mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
    try {
        List<Entries> results = mapper.readValue(new URL("http://collegewires.com/android/jacksoncw.json"), new TypeReference<List<Entries>>(){});
        for(int i=0;i<results.size();++i){
            System.out.println(results.get(i).getName());
            out = out + " ## " + results.get(i).getName();
            txt.setText("1111");
        }
    } catch (JsonParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    } catch (JsonMappingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Entries.java (this is the POJO)

package com.collegewires.jackson;

public class Entries {
public Entries(){
}

private String id, name, email, address, gender;
private Phone phone;

public Phone getPhone() {
    return phone;
}

public void setPhone(Phone phone) {
    this.phone = phone;
}

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

public String getAddress() {
    return address;
}

public void setAddress(String address) {
    this.address = address;
}

public String getGender() {
    return gender;
}

public void setGender(String gender) {
    this.gender = gender;
}

@Override
public String toString() {
    return "Entries:{id: " + id + ", name: " + name + 
                ", email: " + email + ", address: " + address + ", gender: " + gender + ", phone: " + phone + "}";
}

public class Phone {
    public Phone(){
    }
    public String  mobile, home, office;
    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }

    public String getHome() {
        return home;
    }

    public void setHome(String home) {
        this.home = home;
    }

    public String getOffice() {
        return office;
    }

    public void setOffice(String office) {
        this.office = office;
    }

    @Override
    public String toString() {
        return "Phone:{mobile: " + mobile + ", home: " + home + 
                    ", office: " + office + "}";
    }
}


}

Now, I'm getting the following error in my log. Because of this, I'm unable to proceed with my work. Here is the log :

07-12 12:06:13.206: W/System.err(30593): 

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
07-12 12:06:13.206: W/System.err(30593):  at [Source: http://collegewires.com/android/jacksoncw.json; line: 1, column: 1]
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:575)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:569)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.handleNonArray(CollectionDeserializer.java:259)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:207)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:23)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2018)
07-12 12:06:13.211: W/System.err(30593):    at com.collegewires.jackson.MainActivity.onCreate(MainActivity.java:81)
07-12 12:06:13.211: W/System.err(30593):    at android.app.Activity.performCreate(Activity.java:5250)
07-12 12:06:13.211: W/System.err(30593):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2297)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.access$700(ActivityThread.java:152)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1282)
07-12 12:06:13.211: W/System.err(30593):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-12 12:06:13.211: W/System.err(30593):    at android.os.Looper.loop(Looper.java:137)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.main(ActivityThread.java:5328)
07-12 12:06:13.211: W/System.err(30593):    at java.lang.reflect.Method.invokeNative(Native Method)
07-12 12:06:13.211: W/System.err(30593):    at java.lang.reflect.Method.invoke(Method.java:511)
07-12 12:06:13.211: W/System.err(30593):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
07-12 12:06:13.211: W/System.err(30593):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
07-12 12:06:13.211: W/System.err(30593):    at dalvik.system.NativeStart.main(Native Method)
07-12 12:06:13.251: D/libEGL(30593): loaded /vendor/lib/egl/libEGL_POWERVR_SGX544_115.so
07-12 12:06:13.261: D/libEGL(30593): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX544_115.so
07-12 12:06:13.266: D/libEGL(30593): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX544_115.so
07-12 12:06:13.271: I/(30593): !@IMGSRV: DATE: 2013.04.23(11:19:33) | BUILDER: LSI3D | REVISION: e9cd1377d8225457ae40
07-12 12:06:13.346: D/OpenGLRenderer(30593): Enabling debug mode 0
07-12 12:06:31.521: W/IInputConnectionWrapper(30593): setComposingText on inactive InputConnection

Answer 1

Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

The key words here are ArrayList and START_OBJECT token. You cannot deserialize a single object into an array of objects. Try to make sense of doing that and you'll understand why.

You can only deserialize an array of JSON objects into an array or collection of POJO's. Note that, whereas a JSON object is delimited by { } braces, an array is delimited by [ ] brackets, with some number of objects inside of it.

Answer 2

1. Remove the Constructor in Entries & Phone

2. GetEntries results = mapper.readValue(new URL("http://collegewires.com/android/jacksoncw.json"), GetEntries.class);

3. Entries seems to be a parameter in your JSON.

GetEntries.java

package com.collegewires.jackson;

import java.util.List;

public class GetEntries{
    private List<Entries> entries;

    public List<Entries> getEntries(){
        return this.entries;
    }
    public void setEntries(List<Entries> entries){
        this.entries = entries;
    }
}

Entries.java

package com.collegewires.jackson;

import java.util.List;

public class Entries{
    private String address;
    private String email;
    private String gender;
    private String id;
    private String name;
    private Phone phone;

    public String getAddress(){
        return this.address;
    }
    public void setAddress(String address){
        this.address = address;
    }
    public String getEmail(){
        return this.email;
    }
    public void setEmail(String email){
        this.email = email;
    }
    public String getGender(){
        return this.gender;
    }
    public void setGender(String gender){
        this.gender = gender;
    }
    public String getId(){
        return this.id;
    }
    public void setId(String id){
        this.id = id;
    }
    public String getName(){
        return this.name;
    }
    public void setName(String name){
        this.name = name;
    }
    public Phone getPhone(){
        return this.phone;
    }
    public void setPhone(Phone phone){
        this.phone = phone;
    }
}

Phone.java

package com.collegewires.jackson;

import java.util.List;

public class Phone{
    private String home;
    private String mobile;
    private String office;

    public String getHome(){
        return this.home;
    }
    public void setHome(String home){
        this.home = home;
    }
    public String getMobile(){
        return this.mobile;
    }
    public void setMobile(String mobile){
        this.mobile = mobile;
    }
    public String getOffice(){
        return this.office;
    }
    public void setOffice(String office){
        this.office = office;
    }
}

Answer 3

The structor of the json implies that you read it back in an object like this:

class Response{
 private List<Entries> entries = ....
public setEntries(List<Entrie> e)
public getEntries()....

}

and load like this

 Response results = mapper.readValue(new URL("http://collegewires.com/android/jacksoncw.json"), Response.class);

Answer 4

Just put the data inside the [] rather than {} and it will work.

For example:

[
    {
        "id": "1",
        "name":"exemple"
    }
]