I'm trying to build dynamic json request in java to send to my c++ server. I'm using the GSON library.
This is my json example:
{
"nodes": {
"12131231231231241": {
"gToken": {
"token": "AABBCCDDEEFF99001122334455667788"
},
"objects": {
"WATER_CONTROL_1": "0"
}
},
"7682642342432423": {
"userAuthentication": {
"userEmail": "user#mail.com",
"userPassword": "userPassword"
},
"objects": {
"LIGHT_1_CONTROL": "1"
}
}
}
}
If you can see the nodes object is dynamic. Inside him i can have a lot of items (in the example i put two, representing by 12131231231231241 and 7682642342432423). Inside each item the authentication method can be different (by token, by email/password) and inside objects item i can have a lot of different dynamic items too.
The part to send to my c++ server, parse the JSON and do the all validations (authetication for example) is already done and working (i test this json example inside c++ string, encode to json and do the parse, get the all items,etc).
So my problem is to build my class to send the request with some struct to corresponding to this dynamic json.
I already implement some other class to send json to my server and its work because i already know the json expected and on other cases the json have a static/fixed content.
My class for this dynamic json:
public class MonitorControlGetRequestArgs implements SerializableJSON {
Nodes nodes;
public MonitorControlGetRequestArgs() {
nodes = new Nodes();
}
static class Nodes{
public Nodes(){
}
}
public static MonitorControlGetRequestArgs fromStringJson(String data){
try {
Gson gson = new Gson();
return gson.fromJson(data, MonitorControlGetRequestArgs.class);
}
catch(Exception e){
return null;
}
}
public static MonitorControlGetRequestArgs fromBytesJson(byte[] data){
if (data == null)
return null;
try {
String str = new String(data, "utf-8");
return fromStringJson(str);
}
catch (Exception e) {
return null;
}
}
#Override
public String toJsonString(){
try{
Gson gson = new Gson();
return gson.toJson(this);
}
catch(Exception e){
return null;
}
}
#Override
public byte[] toJsonBytes(){
try {
return this.toJsonString().getBytes("utf-8");
}
catch (Exception e){
return null;
}
}
}
I create a static class Nodes empty to show you. In my server c++ i receive the item nodes in json format, but now i have a lot of doubts how to build the struct inside nodes to corresponding to my dynamic json.
I hope you understand my doubts. If you don't understand something tell to me.
EDIT 1 - (try to use the example of Andriy Rymar)
I try to simulate this json:
{
"nodes": {
"1317055040393017962": {
"userAuthentication": {
"userEmail": "rr#rr.com",
"userPassword": "rr123"
}
}
}
}
My request class:
public class MonitorControlGetRequestArgs implements SerializableJSON
{
private final static String nodeTemplate = "\"%s\":%s";
List nodes = new ArrayList<>();
public MonitorControlGetRequestArgs(UserAuthentication userAuthentication)
{
JsonData jsonData = new JsonData();
jsonData.addNode(new Node("1317055040393017962", new NodeObject(userAuthentication)));
}
static class Node
{
private final String nodeName;
private final Object nodeBody;
public Node(String nodeName, Object nodeBody) {
this.nodeName = nodeName;
this.nodeBody = nodeBody;
}
public String getNodeName() {
return nodeName;
}
public Object getNodeBody() {
return nodeBody;
}
}
static class JsonData {
List<Node> nodes = new ArrayList<>();
public void addNode(Node node){
nodes.add(node);
}
}
static class NodeObject
{
UserAuthentication userAuthentication;
public NodeObject(UserAuthentication userAuthentication)
{
this.userAuthentication = userAuthentication;
}
}
public static MonitorControlGetRequestArgs fromStringJson(String data)
{
try
{
Gson gson = new Gson();
return gson.fromJson(data, MonitorControlGetRequestArgs.class);
}
catch(Exception e)
{
return null;
}
}
public static MonitorControlGetRequestArgs fromBytesJson(byte[] data)
{
if (data == null) return null;
try
{
String str = new String(data, "utf-8");
return fromStringJson(str);
}
catch (Exception e)
{
return null;
}
}
#Override
public String toJsonString()
{
try
{
Gson gson = new Gson();
return gson.toJson(this);
}
catch(Exception e)
{
return null;
}
}
#Override
public byte[] toJsonBytes()
{
try
{
return this.toJsonString().getBytes("utf-8");
}
catch (Exception e)
{
return null;
}
}
}
EDIT 2
I will try to explain better,i believe I was not totally explicit. My application java is a REST application that send json to my c++ server. In my server i receive the json, i do the parse, i do the validation, the operations, etc and return back to my java client the response in json too.
For example, imagine that my json request body (to create a new user for example) is something like this:
{
"userInformation": {
"name": "user name",
"age": 33
}
}
For this i don't have any doubts how to do (i already implement a lot of requests very similar). I can create a static class like this:
static class UserInfo
{
String name;
String age;
public UserInfo(String name, String age)
{
this.name = name;
this.age = age;
}
}
And inside a request class (very similar to a class like i copy before - MonitorControlGetRequestArgs) i create a new instance to my UserInfo
UserInfo userInformation = new UserInfo (name, age)
In this case its easy because the request json body is static. I already now that i have a userInformation section and inside i have a name and age. To create a list with userInfo (to create multiple users at same time for example) i already implement things like this.
But now, for this specific case i have this json:
{
"nodes": {
"12131231231231241": {
"gToken": {
"token": "AABBCCDDEEFF99001122334455667788"
},
"objects": {
"WATER_CONTROL_1": "0"
}
},
"7682642342432423": {
"userAuthentication": {
"userEmail": "user#mail.com",
"userPassword": "userPassword"
},
"objects": {
"LIGHT_1_CONTROL": "1"
"LIGHT_3_CONTROL": "0"
}
}
}
}
So in this case i have some problems. In these example i put two items (12131231231231241,7682642342432423) but the user can send more (3,4,5,50,100). In the other hand inside nodes i have two sections (12131231231231241,7682642342432423) but this numbers are some ids that i use in my app and i never know that ids the user will put. In last example ( userInformation ) its simple because i create a userInformation section because i already know that the user always put this section, it is static. In these new json request i dont know, because i never now what value he put, i only know that is a string. The authentication method i dont have problems to create. But other problem that i expected to have is in objects section, because the user can put to a lot of objects and i never know what is the key (in userInformation i know that the keys are always the name and age for example and only exits these two keys, i these new case i dont know what is the keys and what are the number of pair of keys/values he put).
EDIT 3 -
I implement this code and i could almost produce all the structure I need. I'm using the gson same.
Nodes nodes;
public MonitorControlGetRequestArgs(String userEmail, String userPassword, Map <String,String> objects)
{
nodes = new Nodes(userEmail, userPassword, objects);
}
static class Nodes
{
AuthenticationMethod authenticationMethod;
Map <String,String> objects;
public Nodes(String userEmail, String userPassword, Map <String,String> objects)
{
authenticationMethod = new AuthenticationMethod(userEmail, userPassword);
this.objects = objects;
}
}
The result json:
{
"nodes": {
"authenticationMethod": {
"userAuthentication": {
"userEmail": "user#mail.com",
"userPassword": "userPassword"
}
},
"objects": {
"aa": "aaaaaaaaaaaaa",
"bbbbbbb": "bbbbb",
"ccdd": "ccddccdd"
}
}
}
Know i only need to add some struct to support this json:
{
"nodes": {
"7682642342432423": {
"authenticationMethod": {
"userAuthentication": {
"userEmail": "user#mail.com",
"userPassword": "userPassword"
}
},
"objects": {
"0": "Hammersmith & City",
"1": "Circle",
"dasd": "dasda"
}
}
}
}
Note: The objects is a map, so i can put the number of objects string/string that i want. Know i need to do something to support the previous json with the 7682642342432423, 12131231231231241, etc, etc..
EDIT 4 - final
Map <String, Obj> nodes;
public MonitorControlGetRequestArgs(Map <String, Obj> nodes)
{
this.nodes = nodes;
}
static class Obj
{
AuthenticationMethod authenticationMethod;
Map <String,String> objects;
public Obj(String userEmail, String userPassword, Map <String,String> objects)
{
authenticationMethod = new AuthenticationMethod(userEmail, userPassword);
this.objects = objects;
}
}
Json that arrive in my server (like i want)
{
"nodes": {
"12131231231231241": {
"authenticationMethod": {
"userAuthentication": {
"userEmail": "user#mail.com",
"userPassword": "userPassword"
}
},
"objects": {
"aa": "aaaaaaaaaaaaa",
"bbbbbbb": "bbbbb",
"ccdd": "ccddccdd"
}
},
"777777777777777": {
"authenticationMethod": {
"userAuthentication": {
"userEmail": "user#mail.com",
"userPassword": "userPassword"
}
},
"objects": {
"aa": "aaaaaaaaaaaaa",
"bbbbbbb": "bbbbb",
"ccdd": "ccddccdd"
}
}
}
}
Here is improved code from previous example that is more flexible and has better serialization mechanism :
public class ForTestApplication {
public static void main(String[] args) {
NodeArray jsonContainer = new NodeArray(
new Node("nodes", new NodeArray(
new Node("12131231231231241", new NodeArray(
new Node("gToken",
new Node("token", "AABBCCDDEEFF99001122334455667788")),
new Node("objects", new NodeArray(
new Node("WATER_CONTROL_1", "0"),
new Node("WATER_CONTROL_2", "1")
)))),
new Node("7682642342432423", new NodeArray(
new Node("userAuthentication", new NodeArray(
new Node("userEmail","user#mail.com"),
new Node("userPassword","userPassword")
)),
new Node("objects", new NodeArray(
new Node("WATER_CONTROL_1", "0"),
new Node("WATER_CONTROL_2", "1")
))
))
)));
System.out.println(jsonContainer.toJSONString());
}
}
class NodeArray {
private static final String NODE_TEMPLATE = "\"%s\":%s";
private static final Gson gson = new Gson();
private List<Node> nodes = new ArrayList<>();
public NodeArray(Node... nodes){
addNode(nodes);
}
public void addNode(Node... node){
nodes.addAll(Arrays.asList(node));
}
public String toJSONString() {
return nodes.stream()
.map(node -> String.format(NODE_TEMPLATE, node.getNodeName(), getNodeBodyAsJSON(node)))
.collect(Collectors.joining(",", "{", "}"));
}
private String getNodeBodyAsJSON(Node node) {
if (node.getNodeBody() instanceof NodeArray) {
return ((NodeArray) node.getNodeBody()).toJSONString();
}
return gson.toJson(node.getNodeBody());
}
}
class Node {
private final String nodeName;
private final Object nodeBody;
public Node(String nodeName, Object nodeBody) {
this.nodeName = nodeName;
this.nodeBody = nodeBody;
}
public String getNodeName() {
return nodeName;
}
public Object getNodeBody() {
return nodeBody;
}
}
The output of such application is :
{"nodes":{"12131231231231241":{"gToken":{"nodeName":"token","nodeBody":"AABBCCDDEEFF99001122334455667788"},"objects":{"WATER_CONTROL_1":"0","WATER_CONTROL_2":"1"}},"7682642342432423":{"userAuthentication":{"userEmail":"user#mail.com","userPassword":"userPassword"},"objects":{"WATER_CONTROL_1":"0","WATER_CONTROL_2":"1"}}}}
Pretty view is :
NOTICE : this example use constructors to build complex structures but I highly recommend to use builder pattern for such case. Code will be clearer and better.
Here is example of what you need using Gson. But if you would like to use something else, for example OrgJson then the code will be more clear and without String templates.
public class ForTestApplication {
private final static String nodeTemplate = "\"%s\":%s";
public static void main(String[] args) {
JsonData jsonData = new JsonData();
jsonData.addNode(new Node("user-1", new TestObject(62, "James", "Gosling")));
jsonData.addNode(new Node("user-2", new TestObject(53, "James", "Hetfield")));
System.out.println(jsonData.toJSONStirng());
}
static class JsonData {
List<Node> nodes = new ArrayList<>();
public void addNode(Node node){
nodes.add(node);
}
public String toJSONStirng() {
Gson gson = new Gson();
return nodes.stream()
.map(node -> String.format(nodeTemplate, node.getNodeName(), gson.toJson(node.getNodeBody())))
.collect(Collectors.joining(",", "{", "}"));
}
}
static class Node {
private final String nodeName;
private final Object nodeBody;
public Node(String nodeName, Object nodeBody) {
this.nodeName = nodeName;
this.nodeBody = nodeBody;
}
public String getNodeName() {
return nodeName;
}
public Object getNodeBody() {
return nodeBody;
}
}
static class TestObject {
private int age;
private String firstName;
private String lastName;
public TestObject(int age, String firstName, String lastName) {
this.age = age;
this.firstName = firstName;
this.lastName = lastName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
}
Output :
{"user-1":{"age":62,"firstName":"James","lastName":"Gosling"},"user-2":{"age":53,"firstName":"James","lastName":"Hetfield"}}
Pretty view :
I am using Jackson to deserialize a JSON string into an enum.
public enum RoomType {
SHARED("shared"),
PRIVATE("private");
private String value;
RoomType(String value) {
this.value = value;
}
#JsonCreator
public static RoomType fromJson(final String jsonValue) {
for (RoomType type : values()) {
if (type.value.equals(jsonValue)) {
return type;
}
}
return null;
}
#JsonValue
#Override
public String toString() {
return value;
}
}
I want to unit test the different edge cases:
#RunWith(JUnit4.class)
public class RoomTypeTest {
private final ObjectMapper mapper = new ObjectMapper();
#Test
public void fromJsonWithShared() throws Exception {
String json = "{\"roomType\":\"shared\"}";
RoomType type = mapper.readValue(json, RoomType.class);
assertThat(type).isEqualTo(RoomType.SHARED);
}
}
The test fails. When I debug I see that jsonValue is null when RoomType.fromJson is invoked. Seems like that Jackson does not pick up the value from the JSON string.
Related examples
EnumCreatorTest929.java
I think Jackson doesn't know what value to pass to that fromJson method. Try adding #JsonProperty:
#JsonCreator
public static RoomType fromJson(#JsonProperty("roomType") final String jsonValue) {
....
}
I have a JSON object that looks like this
{
id:int,
tags: [
"string",
"string"
],
images: {
waveform_l:"url_to_image",
waveform_m:"url_to_image",
spectral_m:"url_to_image",
spectral_l:"url_to_image"
}
}
I'm trying to use retrofit to parse the JSON and create the interface. The problem that I have is that I get a null for the images urls. Everything else works, I am able to retrieve the id, the tags, but when I try to get the images they are all null.
I have a sound pojo that looks like this:
public class Sound {
private Integer id;
private List<String> tags = new ArrayList<String>();
private Images images;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Images getImages() {
return images;
}
public void setImages(Images images) {
this.images = images;
}
... setters and getter for tags as well
}
and I have a Images pojo that looks like this:
public class Images {
private String waveformL;
private String waveformM;
private String spectralM;
private String spectralL;
public String getWaveformL() {
return waveformL;
}
public void setWaveformL(String waveformL) {
this.waveformL = waveformL;
}
public String getWaveformM() {
return waveformM;
}
public void setWaveformM(String waveformM) {
this.waveformM = waveformM;
}
public String getSpectralM() {
return spectralM;
}
public void setSpectralM(String spectralM) {
this.spectralM = spectralM;
}
public String getSpectralL() {
return spectralL;
}
public void setSpectralL(String spectralL) {
this.spectralL = spectralL;
}
}
Whenever I try to call images.getWaveformM() it gives me a null pointer. Any ideas?
#SerializedName can also be used to solve this. It allows you to match the expected JSON format without having to declare your Class variable exactly the same way.
public class Images {
#SerializedName("waveform_l")
private String waveformL;
#SerializedName("waveform_m")
private String waveformM;
#SerializedName("spectral_m")
private String spectralM;
#SerializedName("spectral_l")
private String spectralL;
...
}
If the only differences from the JSON to your class variables are the snake/camel case then perhaps #njzk2 answer works better but in cases where there's more differences outside those bounds then #SerializeName can be your friend.
You possibly need this part:
Gson gson = new GsonBuilder()
.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
.create();
setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES) will allow gson to automatically transform the snake case into camel case.
public class Images {
private String waveform_l;
private String waveform_m;
private String spectral_m;
private String spectral_m;
}
Key name should be same in model as in json other wise it won't recognise it else you haven't define it at GsonBuilder creation.Generate the getter setter for the same and you will be good to go
I am using Retrofit to make a HTTP request which returns an array of object and I am getting the following errors:
com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY
The response returned is expected to be like this:
[ {key1: "value1", key2: "value2"}, {key1: "value1", key2: "value2"}, ... ]
I have the following class, for serializing the data:
public class data {
private List<element> dataList;
public List<element> getElements() {
return dataList;
}
public class element {
#SerializedName("key1")
private String key1;
#SerializedName("key2")
private String key2;
// Getters and Setters
}
}
Please let me know if you have any ideas. Thanks
The error was actually in my implementation of Retrofit Callback. My implementation was expecting an object when it should be expecting an array in this case. Thanks everyone for the help.
Before
//*****MyData*****//
public class MyData {
private List<Data> dataList;
public List<Data> getElements() {
return dataList;
}
public class Data {
#SerializedName("key1")
private String key1;
#SerializedName("key2")
private String key2;
// Getters and Setters
}
}
//*****Callback Implementation*****//
public class MyDataCallback extends Callback {
public MyDataCallback(MyDataCallbackListener<MyData> myDataCallbackListener) {
super(myDataCallbackListener);
}
#Override
public void success(MyData data, Response response) {
if (myDataCallbackListener != null) {
myDataCallbackListener.onCallbackComplete(true, response, MyDataCallback.CALLBACK_SUCCESS_MESSAGE, data);
}
}
}
After
//*****Data*****//
public class Data {
#SerializedName("key1")
private String key1;
#SerializedName("key2")
private String key2;
// Getters and Setters
}
//*****Callback Implementation*****//
public class MyDataCallback extends Callback {
public MyDataCallback(MyDataCallbackListener<List<Data>> myDataCallbackListener) {
super(myDataCallbackListener);
}
#Override
public void success(List<Data> data, Response response) {
if (myDataCallbackListener != null) {
myDataCallbackListener.onCallbackComplete(true, response, MyDataCallback.CALLBACK_SUCCESS_MESSAGE, data);
}
}
}
As Dave mentioned in his comment, it does seem strange that you have recursion in the class that I am assuming is your response object. (your class "data" has a list of "data" objects).
I would suggest something a little more strait forward such as this:
public class ResponseObject {
private ArrayList<DataObject> mDataObjects;
public ArrayList<DataObject> getDataObjects() {
return mDataObjects;
}
private class DataObject {
private String key1;
private String key2;
public String getKey1() {
return key1;
}
public String getKey2() {
return key2;
}
}
}
or since you are local maybe you can buy Jake a beer :) From his photo, I would check Rouge Ales, 21 Amendment or my favorite last time I was in SF - Magnolia
It's not valid JSON to begin with an array. You need to instead return something like this:
{
dataList: [
{
key1: "value1",
key2: "value2"
},
{
key1: "value3",
key2: "value4"
}
]
}
Then you can use GSON to deserialize that into your data class.
in my Android application, I am returned a simple JSON object with simple key value pairs, eg:
{"username" : "billySmith", "gender" : 1}
And an enum with the respective field names username and gender (String and int, respectively).
I am trying to use Gson to parse the JSON object and populate the enum fields with the json values. I am a little uncertain of how to use GSON with enums. I am familiar with the concept that an instance of an object should be set equal to gson.fromJson(jsonObect, instanceType.class);.
To add more detail, I am using Enums so that the values can be retrieved from anywhere in my android project.
if (response.getStatusLine().getStatusCode() == 200 && result != "")
{
GlobalEnum globalEnum = GlobalEnum.getInstance();
Gson gson = new GsonBuilder().create();
globalEnum = gson.fromJson(result, GlobalEnum.class);
}
where "result" is the string representation of an HTTP Response's entity
GlobalEnum snippet:
public enum GlobalEnum
{
INSTANCE;
private String username;
private int gender;
public static GlobalEnum getInstance()
{
return INSTANCE;
}
public int getGender()
{
return gender;
}
public void setGender(int gender)
{
this.gender = gender;
}
}
*Edit:
Reworded: I have an enum, and I have a jsonObject. Both the enum and JSON object have "username" and "gender". using Gson, I would like to parse the JSON object so that the Values from the JSONobject will be assigned to the respective fields in the Enum.
You may have misunderstood the meaning of an Enum in Java. They usually shouldn't be opened to modifications on runtime like this.
I guess the following logic would serve you better, saving you from this kind of trouble when parsing JSON into Enums.
First, a UserInformation Java Bean class, wrapping the username and gender fields:
public class UserInformation
{
private String username;
private int gender;
public UserInformation(String username, int gender)
{
this.username = username;
this.gender = gender;
}
public String getUsername()
{
return username;
}
public void setUsername(String username)
{
this.username = username;
}
public int getGender()
{
return gender;
}
public void setGender(int gender)
{
this.gender = gender;
}
}
Then your GlobalEnum class, renamed to GlobalValues and modified to work as a value container:
public abstract class GlobalValues
{
// You can also create get/set methods for encapsulation if you want
public static UserInformation userInformation;
}
And then the logic on which you are parsing your JSON String into your UserInformation object, and then storing it on your GlobalValues class.
String jsonStr = "{\"username\" : \"billySmith\", \"gender\" : 1}";
Gson gson = new Gson();
GlobalValues.userInformation = gson.fromJson(jsonStr, UserInformation.class);
As I said in the comment you need create a type adapter to be able to get your enum during json parsing. This is an example of what i have done for my purposes.
In your enum create TypeAdapterFactory gsonTypeAdaptor like so:
public static TypeAdapterFactory gsonTypeAdaptor = new TypeAdapterFactory() {
#Override
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
Class<T> rawType = (Class<T>) type.getRawType();
if (!(rawType.isEnum() && Predicates.assignableFrom(rawType).apply(<your enum>.class))) {
return null;
}
return new TypeAdapter<T>() {
public void write(JsonWriter out, T value) throws IOException {
if (value == null) {
out.nullValue();
} else {
out.value(((<your enum>)value).name);
}
}
public T read(JsonReader reader) throws IOException {
if (reader.peek() == JsonToken.NULL) {
reader.nextNull();
return null;
} else {
return (T) <get your enum by using reader.nextString()>;
}
}
};
}
};
one adapter is in place, register it with your gson builder like so:
builder.registerTypeAdapterFactory(<your enum>.gsonTypeAdaptor);
Let me know if this was useful.