I am writing a web service the first time. I created a RESTful web service based on Jersey. And I want to produce JSON. What do I need to do to generate the correct JSON type of my web service?
Here's one of my methods:
#GET
#Path("/friends")
#Produces("application/json")
public String getFriends() {
return "{'friends': ['Michael', 'Tom', 'Daniel', 'John', 'Nick']}";
}
Is it sufficient that I simply point out annotation #Produces("application/json") for my method? Then this method may return any type of object? Or only String? Do I need additional processing or transformation of these objects?
Please help me as a beginner to deal with these issues. Thanks in advance!
You can annotate your bean with jaxb annotations.
#XmlRootElement
public class MyJaxbBean {
public String name;
public int age;
public MyJaxbBean() {} // JAXB needs this
public MyJaxbBean(String name, int age) {
this.name = name;
this.age = age;
}
}
and then your method would look like this:
#GET #Produces("application/json")
public MyJaxbBean getMyBean() {
return new MyJaxbBean("Agamemnon", 32);
}
There is a chapter in the latest documentation that deals with this:
https://jersey.java.net/documentation/latest/user-guide.html#json
You could use a package like org.json http://www.json.org/java/
Because you will need to use JSONObjects more often.
There you can easily create JSONObjects and put some values in it:
JSONObject json = new JSONObject();
JSONArray array=new JSONArray();
array.put("1");
array.put("2");
json.put("friends", array);
System.out.println(json.toString(2));
{"friends": [
"1",
"2"
]}
edit This has the advantage that you can build your responses in different layers and return them as an object
#GET
#Path("/friends")
#Produces(MediaType.APPLICATION_JSON)
public String getFriends() {
// here you can return any bean also it will automatically convert into json
return "{'friends': ['Michael', 'Tom', 'Daniel', 'John', 'Nick']}";
}
#POST
#Path ("Employee")
#Consumes("application/json")
#Produces("application/json")
public JSONObject postEmployee(JSONObject jsonObject)throws Exception{
return jsonObject;
}
Use this annotation
#RequestMapping(value = "/url", method = RequestMethod.GET, produces = {MediaType.APPLICATION_JSON})
Related
I have a sample RestController in Spring Boot:
#RestController
#RequestMapping("/api")
class MyRestController
{
#GetMapping(path = "/hello")
public JSONObject sayHello()
{
return new JSONObject("{'aa':'bb'}");
}
}
I am using the JSON library org.json
When I hit API /hello, I get an exception saying :
Servlet.service() for servlet [dispatcherServlet] in context with path
[] threw exception [Request processing failed; nested exception is
java.lang.IllegalArgumentException: No converter found for return
value of type: class org.json.JSONObject] with root cause
java.lang.IllegalArgumentException: No converter found for return
value of type: class org.json.JSONObject
What is the issue? Can someone explain what exactly is happening?
As you are using Spring Boot web, Jackson dependency is implicit and we do not have to define explicitly. You can check for Jackson dependency in your pom.xml in the dependency hierarchy tab if using eclipse.
And as you have annotated with #RestController there is no need to do explicit json conversion. Just return a POJO and jackson serializer will take care of converting to json. It is equivalent to using #ResponseBody when used with #Controller. Rather than placing #ResponseBody on every controller method we place #RestController instead of vanilla #Controller and #ResponseBody by default is applied on all resources in that controller. Refer this link: https://docs.spring.io/spring/docs/current/spring-framework-reference/html/mvc.html#mvc-ann-responsebody
The problem you are facing is because the returned object(JSONObject) does not have getter for certain properties. And your intention is not to serialize this JSONObject but instead to serialize a POJO. So just return the POJO.
Refer this link: https://stackoverflow.com/a/35822500/5039001
If you want to return a json serialized string then just return the string. Spring will use StringHttpMessageConverter instead of JSON converter in this case.
The reason why your current approach doesn't work is because Jackson is used by default to serialize and to deserialize objects. However, it doesn't know how to serialize the JSONObject. If you want to create a dynamic JSON structure, you can use a Map, for example:
#GetMapping
public Map<String, String> sayHello() {
HashMap<String, String> map = new HashMap<>();
map.put("key", "value");
map.put("foo", "bar");
map.put("aa", "bb");
return map;
}
This will lead to the following JSON response:
{ "key": "value", "foo": "bar", "aa": "bb" }
This is a bit limited, since it may become a bit more difficult to add child objects. Jackson has its own mechanism though, using ObjectNode and ArrayNode. To use it, you have to autowire ObjectMapper in your service/controller. Then you can use:
#GetMapping
public ObjectNode sayHello() {
ObjectNode objectNode = mapper.createObjectNode();
objectNode.put("key", "value");
objectNode.put("foo", "bar");
objectNode.put("number", 42);
return objectNode;
}
This approach allows you to add child objects, arrays, and use all various types.
You can either return a response as String as suggested by #vagaasen or you can use ResponseEntity Object provided by Spring as below. By this way you can also return Http status code which is more helpful in webservice call.
#RestController
#RequestMapping("/api")
public class MyRestController
{
#GetMapping(path = "/hello", produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> sayHello()
{
//Get data from service layer into entityList.
List<JSONObject> entities = new ArrayList<JSONObject>();
for (Entity n : entityList) {
JSONObject entity = new JSONObject();
entity.put("aa", "bb");
entities.add(entity);
}
return new ResponseEntity<Object>(entities, HttpStatus.OK);
}
}
you can also use a hashmap for this
#GetMapping
public Map<String, Object> get() {
Map<String, Object> map = new HashMap<>();
map.put("key1", "value1");
map.put("results", somePOJO);
return map;
}
More correct create DTO for API queries, for example entityDTO:
Default response OK with list of entities:
#GetMapping(produces=MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public List<EntityDto> getAll() {
return entityService.getAllEntities();
}
But if you need return different Map parameters you can use next two examples
2. For return one parameter like map:
#GetMapping(produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> getOneParameterMap() {
return ResponseEntity.status(HttpStatus.CREATED).body(
Collections.singletonMap("key", "value"));
}
And if you need return map of some parameters(since Java 9):
#GetMapping(produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> getSomeParameters() {
return ResponseEntity.status(HttpStatus.OK).body(Map.of(
"key-1", "value-1",
"key-2", "value-2",
"key-3", "value-3"));
}
#RequestMapping("/api/status")
public Map doSomething()
{
return Collections.singletonMap("status", myService.doSomething());
}
PS. Works only for 1 value
If you need to return a JSON object using a String, then the following should work:
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.ResponseEntity;
...
#RestController
#RequestMapping("/student")
public class StudentController {
#GetMapping
#RequestMapping("/")
public ResponseEntity<JsonNode> get() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
JsonNode json = mapper.readTree("{\"id\": \"132\", \"name\": \"Alice\"}");
return ResponseEntity.ok(json);
}
...
}
use ResponseEntity<ResponseBean>
Here you can use ResponseBean or Any java bean as you like to return your api response and it is the best practice. I have used Enum for response. it will return status code and status message of API.
#GetMapping(path = "/login")
public ResponseEntity<ServiceStatus> restApiExample(HttpServletRequest request,
HttpServletResponse response) {
String username = request.getParameter("username");
String password = request.getParameter("password");
loginService.login(username, password, request);
return new ResponseEntity<ServiceStatus>(ServiceStatus.LOGIN_SUCCESS,
HttpStatus.ACCEPTED);
}
for response ServiceStatus or(ResponseBody)
public enum ServiceStatus {
LOGIN_SUCCESS(0, "Login success"),
private final int id;
private final String message;
//Enum constructor
ServiceStatus(int id, String message) {
this.id = id;
this.message = message;
}
public int getId() {
return id;
}
public String getMessage() {
return message;
}
}
Spring REST API should have below key in response
Status Code
Message
you will get final response below
{
"StatusCode" : "0",
"Message":"Login success"
}
you can use ResponseBody(java POJO, ENUM,etc..) as per your requirement.
I use to return Map<String,Object> in the Controller by using the toMap() method of org.json.JSONObject as follows.
#GetMapping("/json")
public Map<String, Object> getJsonOutput() {
JSONObject jsonObject = new JSONObject();
//construct jsonObject here
return jsonObject.toMap();
}
you can do this :
#RestController
#RequestMapping("/api")
class MyRestController
{
#GetMapping(path = "/hello")
public JSONObject sayHello()
{
return new JSONObject("{'aa':'bb'}").toMap();;
}
}
I have a sample RestController in Spring Boot:
#RestController
#RequestMapping("/api")
class MyRestController
{
#GetMapping(path = "/hello")
public JSONObject sayHello()
{
return new JSONObject("{'aa':'bb'}");
}
}
I am using the JSON library org.json
When I hit API /hello, I get an exception saying :
Servlet.service() for servlet [dispatcherServlet] in context with path
[] threw exception [Request processing failed; nested exception is
java.lang.IllegalArgumentException: No converter found for return
value of type: class org.json.JSONObject] with root cause
java.lang.IllegalArgumentException: No converter found for return
value of type: class org.json.JSONObject
What is the issue? Can someone explain what exactly is happening?
As you are using Spring Boot web, Jackson dependency is implicit and we do not have to define explicitly. You can check for Jackson dependency in your pom.xml in the dependency hierarchy tab if using eclipse.
And as you have annotated with #RestController there is no need to do explicit json conversion. Just return a POJO and jackson serializer will take care of converting to json. It is equivalent to using #ResponseBody when used with #Controller. Rather than placing #ResponseBody on every controller method we place #RestController instead of vanilla #Controller and #ResponseBody by default is applied on all resources in that controller. Refer this link: https://docs.spring.io/spring/docs/current/spring-framework-reference/html/mvc.html#mvc-ann-responsebody
The problem you are facing is because the returned object(JSONObject) does not have getter for certain properties. And your intention is not to serialize this JSONObject but instead to serialize a POJO. So just return the POJO.
Refer this link: https://stackoverflow.com/a/35822500/5039001
If you want to return a json serialized string then just return the string. Spring will use StringHttpMessageConverter instead of JSON converter in this case.
The reason why your current approach doesn't work is because Jackson is used by default to serialize and to deserialize objects. However, it doesn't know how to serialize the JSONObject. If you want to create a dynamic JSON structure, you can use a Map, for example:
#GetMapping
public Map<String, String> sayHello() {
HashMap<String, String> map = new HashMap<>();
map.put("key", "value");
map.put("foo", "bar");
map.put("aa", "bb");
return map;
}
This will lead to the following JSON response:
{ "key": "value", "foo": "bar", "aa": "bb" }
This is a bit limited, since it may become a bit more difficult to add child objects. Jackson has its own mechanism though, using ObjectNode and ArrayNode. To use it, you have to autowire ObjectMapper in your service/controller. Then you can use:
#GetMapping
public ObjectNode sayHello() {
ObjectNode objectNode = mapper.createObjectNode();
objectNode.put("key", "value");
objectNode.put("foo", "bar");
objectNode.put("number", 42);
return objectNode;
}
This approach allows you to add child objects, arrays, and use all various types.
You can either return a response as String as suggested by #vagaasen or you can use ResponseEntity Object provided by Spring as below. By this way you can also return Http status code which is more helpful in webservice call.
#RestController
#RequestMapping("/api")
public class MyRestController
{
#GetMapping(path = "/hello", produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> sayHello()
{
//Get data from service layer into entityList.
List<JSONObject> entities = new ArrayList<JSONObject>();
for (Entity n : entityList) {
JSONObject entity = new JSONObject();
entity.put("aa", "bb");
entities.add(entity);
}
return new ResponseEntity<Object>(entities, HttpStatus.OK);
}
}
you can also use a hashmap for this
#GetMapping
public Map<String, Object> get() {
Map<String, Object> map = new HashMap<>();
map.put("key1", "value1");
map.put("results", somePOJO);
return map;
}
More correct create DTO for API queries, for example entityDTO:
Default response OK with list of entities:
#GetMapping(produces=MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public List<EntityDto> getAll() {
return entityService.getAllEntities();
}
But if you need return different Map parameters you can use next two examples
2. For return one parameter like map:
#GetMapping(produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> getOneParameterMap() {
return ResponseEntity.status(HttpStatus.CREATED).body(
Collections.singletonMap("key", "value"));
}
And if you need return map of some parameters(since Java 9):
#GetMapping(produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> getSomeParameters() {
return ResponseEntity.status(HttpStatus.OK).body(Map.of(
"key-1", "value-1",
"key-2", "value-2",
"key-3", "value-3"));
}
#RequestMapping("/api/status")
public Map doSomething()
{
return Collections.singletonMap("status", myService.doSomething());
}
PS. Works only for 1 value
If you need to return a JSON object using a String, then the following should work:
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.ResponseEntity;
...
#RestController
#RequestMapping("/student")
public class StudentController {
#GetMapping
#RequestMapping("/")
public ResponseEntity<JsonNode> get() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
JsonNode json = mapper.readTree("{\"id\": \"132\", \"name\": \"Alice\"}");
return ResponseEntity.ok(json);
}
...
}
use ResponseEntity<ResponseBean>
Here you can use ResponseBean or Any java bean as you like to return your api response and it is the best practice. I have used Enum for response. it will return status code and status message of API.
#GetMapping(path = "/login")
public ResponseEntity<ServiceStatus> restApiExample(HttpServletRequest request,
HttpServletResponse response) {
String username = request.getParameter("username");
String password = request.getParameter("password");
loginService.login(username, password, request);
return new ResponseEntity<ServiceStatus>(ServiceStatus.LOGIN_SUCCESS,
HttpStatus.ACCEPTED);
}
for response ServiceStatus or(ResponseBody)
public enum ServiceStatus {
LOGIN_SUCCESS(0, "Login success"),
private final int id;
private final String message;
//Enum constructor
ServiceStatus(int id, String message) {
this.id = id;
this.message = message;
}
public int getId() {
return id;
}
public String getMessage() {
return message;
}
}
Spring REST API should have below key in response
Status Code
Message
you will get final response below
{
"StatusCode" : "0",
"Message":"Login success"
}
you can use ResponseBody(java POJO, ENUM,etc..) as per your requirement.
I use to return Map<String,Object> in the Controller by using the toMap() method of org.json.JSONObject as follows.
#GetMapping("/json")
public Map<String, Object> getJsonOutput() {
JSONObject jsonObject = new JSONObject();
//construct jsonObject here
return jsonObject.toMap();
}
you can do this :
#RestController
#RequestMapping("/api")
class MyRestController
{
#GetMapping(path = "/hello")
public JSONObject sayHello()
{
return new JSONObject("{'aa':'bb'}").toMap();;
}
}
Am developing a rest webservice using Jersey.Am slightly new to webservices. I need to pass List of customer as input to rest webservice. having issue in achieving it.
Below is my customer object class
#Component
public class customer {
private String customerId;
private String customerName;
And my endpoint is as below. addCust is the method that will be called on calling the webservice
#Path("/add")
#Produces({MediaType.APPLICATION_JSON})
#Consumes({MediaType.APPLICATION_JSON})
public String addCust(#Valid customer[] customers){
//And json input is as below
{customers:{"customerId":"1","customerName":"a"},
{"customerId":"2","customerName":"b"}}
But jersey is not able to convert json array to Array of Customers. It is returning 400. And the logs shows "no viable alternative at c". How to pass Json array as input to webservice and convert into Array or ArrayList. Any help appreciated.
Your json is invalid, field names should be always double quotted, and arrays are placed inside [] for example:
{"customers":[{"customerId":"1","customerName":"a"},
{"customerId":"2","customerName":"b"}]}
thats why jackson cannot unmarshall it. But this json will never fit your api.
Here is an example of what You should send:
[{"customerId":"1","customerName":"a"},{"customerId":"2","customerName":"b"}]
Another thing is that You can use collections instead of arrays:
#Path("/add")
#Produces({MediaType.APPLICATION_JSON})
#Consumes({MediaType.APPLICATION_JSON})
public String addCust(#Valid List<Customer> customers){
If you want to send a json like this:
{"customers":[{"customerId":"1","customerName":"a"},
{"customerId":"2","customerName":"b"}]}
then you have to wrap everything into class with "customers" property:
class AddCustomersRequest {
private List<Customer> customers;
public void setCustomers(List<Customer> customers) {
this.customers = customers;
}
public void getCustomers() {
return this.customers;
}
}
And use it in Your API:
#Path("/add")
#Produces({MediaType.APPLICATION_JSON})
#Consumes({MediaType.APPLICATION_JSON})
public String addCust(#Valid AddCustomersRequest customersReq){
I have a rest webservice. For some reason I don't want to return class which needed to be converted to interface. I want to return interface and in the JSON I want to see only the methods(which starts get) values. Not the all attributes from the implemented class.
Say for an example:
#Path("getValues/")
#GET
#Produces( MediaType.APPLICATION_JSON)
public DetailInterface getClientDetail() {
return new DetailImpl();
}
and consider the interface:
public interface DetailInterface {
public String getName();
public String getAge();
}
and consider the implementation
public class DetailImpl implements DetailInterface {
public String getName()
return "my name";
}
public String getAge(){
return "my age";
}
public String iDontWantThisinJSON() {
return "I don't want this in JSON output";
}
}
when I request the rest service I see the iDontWantThisinJSON attribute also comes in the JSON response. I don't want to include it in the response.
How can I fix this?
Have you tried #JsonIgnore annotation? Marking the field as transient may be also helpful - however I'm not sure if it's ok.
This is a more of a java concept than Rest or Json. You will have to modify the code as follows and it should work as you want it to work.
#Path("getValues/")
#GET
#Produces( MediaType.APPLICATION_JSON)
public DetailInterface getClientDetail() {
DetailInterface di = new DetailImpl()
return di;
}
I have
#RequestMapping(method = RequestMethod.GET)
#ResponseBody
SessionInfo register(UserProfile profileJson){
...
}
I pass profileJson this way:
http://server/url?profileJson={"email": "mymail#gmail.com"}
but my profileJson object has all null fields. What should I do to make spring parse my json?
The solution to this is so easy and simple it will practically make you laugh, but before I even get to it, let me first emphasize that no self-respecting Java developer would ever, and I mean EVER work with JSON without utilizing the Jackson high-performance JSON library.
Jackson is not only a work horse and a defacto JSON library for Java developers, but it also provides a whole suite of API calls that makes JSON integration with Java a piece of cake (you can download Jackson at http://jackson.codehaus.org/).
Now for the answer. Assuming that you have a UserProfile pojo that looks something like this:
public class UserProfile {
private String email;
// etc...
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
// more getters and setters...
}
...then your Spring MVC method to convert a GET parameter name "profileJson" with JSON value of {"email": "mymail#gmail.com"} would look like this in your controller:
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper; // this is your lifesaver right here
//.. your controller class, blah blah blah
#RequestMapping(value="/register", method = RequestMethod.GET)
public SessionInfo register(#RequestParam("profileJson") String profileJson)
throws JsonMappingException, JsonParseException, IOException {
// now simply convert your JSON string into your UserProfile POJO
// using Jackson's ObjectMapper.readValue() method, whose first
// parameter your JSON parameter as String, and the second
// parameter is the POJO class.
UserProfile profile =
new ObjectMapper().readValue(profileJson, UserProfile.class);
System.out.println(profile.getEmail());
// rest of your code goes here.
}
Bam! You're done. I would encourage you to look through the bulk of Jackson API because, as I said, it is a lifesaver. For example, are you returning JSON from your controller at all? If so, all you need to do is include JSON in your lib, and return your POJO and Jackson will AUTOMATICALLY convert it into JSON. You can't get much easier than that. Cheers! :-)
This could be done with a custom editor, that converts the JSON into a UserProfile object:
public class UserProfileEditor extends PropertyEditorSupport {
#Override
public void setAsText(String text) throws IllegalArgumentException {
ObjectMapper mapper = new ObjectMapper();
UserProfile value = null;
try {
value = new UserProfile();
JsonNode root = mapper.readTree(text);
value.setEmail(root.path("email").asText());
} catch (IOException e) {
// handle error
}
setValue(value);
}
}
This is for registering the editor in the controller class:
#InitBinder
public void initBinder(WebDataBinder binder) {
binder.registerCustomEditor(UserProfile.class, new UserProfileEditor());
}
And this is how to use the editor, to unmarshall the JSONP parameter:
#RequestMapping(value = "/jsonp", method = RequestMethod.GET, produces = {MediaType.APPLICATION_JSON_VALUE})
#ResponseBody
SessionInfo register(#RequestParam("profileJson") UserProfile profileJson){
...
}
You can create your own Converter and let Spring use it automatically where appropriate:
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;
#Component
class JsonToUserProfileConverter implements Converter<String, UserProfile> {
private final ObjectMapper jsonMapper = new ObjectMapper();
public UserProfile convert(String source) {
return jsonMapper.readValue(source, UserProfile.class);
}
}
As you can see in the following controller method nothing special is needed:
#GetMapping
#ResponseBody
public SessionInfo register(#RequestParam UserProfile userProfile) {
...
}
Spring picks up the converter automatically if you're using component scanning and annotate the converter class with #Component.
Learn more about Spring Converter and type conversions in Spring MVC.
This does solve my immediate issue, but I'm still curious as to how you might pass in multiple JSON objects via an AJAX call.
The best way to do this is to have a wrapper object that contains the two (or multiple) objects you want to pass. You then construct your JSON object as an array of the two objects i.e.
[
{
"name" : "object1",
"prop1" : "foo",
"prop2" : "bar"
},
{
"name" : "object2",
"prop1" : "hello",
"prop2" : "world"
}
]
Then in your controller method you recieve the request body as a single object and extract the two contained objects. i.e:
#RequestMapping(value="/handlePost", method = RequestMethod.POST, consumes = { "application/json" })
public void doPost(#RequestBody WrapperObject wrapperObj) {
Object obj1 = wrapperObj.getObj1;
Object obj2 = wrapperObj.getObj2;
//Do what you want with the objects...
}
The wrapper object would look something like...
public class WrapperObject {
private Object obj1;
private Object obj2;
public Object getObj1() {
return obj1;
}
public void setObj1(Object obj1) {
this.obj1 = obj1;
}
public Object getObj2() {
return obj2;
}
public void setObj2(Object obj2) {
this.obj2 = obj2;
}
}
Just add #RequestBody annotation before this param