I searched for the use of #ResponseBody annotation and I found that this annotation binds data to the response according to the return type of the method here(https://zetcode.com/springboot/responsebody/),But today I got an old project where I saw a controller method like this:-
#Controller
public class MyConroller {
#Autowired
JsonMapper mapper;
#RequestMapping(value = "/methodURL", method = RequestMethod.GET)
#ResponseBody
public void controllerMethod(HttpServletRequest req, HttpServletResponse res) {
HttpSession hs = req.getSession(false);
Map<String, Object> map = service.getList();
mapper.WritecInJson(res, map);
}
}
JASON Mapper-:
public class JsonMapper {
public void WritecInJson(HttpServletResponse res,Object object)
{
MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
MediaType jsonMimeType = MediaType.APPLICATION_JSON;
if(jsonConverter.canWrite(object.getClass(), jsonMimeType)){
jsonConverter.write(object , jsonMimeType, new ServletServerHttpResponse(res));
}
}
As you can see the method in the controller class has void as its return type. So, How #ResponseBody binds data to the response through this void method?
#ResponseBody
must defined a return type. If you really don’t need to define a method with return type. You can use HttpServletResponse.getOutputStream() to write back the response content.
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 post request with URL http://my-custom-url/{param}
now
//pseudo code
if param == param1
then request body must be mapped to model Class A
if param == param2
then request body must be mapped to model Class B
In addition to mapping I also have Jsr303 validation inside my model class es hence I also want to use #Valid annotation
How do I do this
You can receive the payload as a Map<K, V> and use ObjectMapper to deserialize it.
#RestController
#RequestMapping(path = "/my-rest-api")
public class MyController {
#Autowired
ClassAValidator classAValidator; // assuming you wrote an validator
#Autowired
ClassBValidator classBValidator; // assuming you wrote an validator
#PostMapping("/{parameter}")
public ResponseEntity<Object> handleRequest(
#PathVariable("parameter") String parameter,
#RequestBody Map<Object, Object> request,
BindingResult result) {
ObjectMapper mapper = new ObjectMapper();
if (parameter.equals("X")) {
ClassA classA = mapper.convertValue(request, ClassA.class);
classAValidator.validate(classA, result);
if(result.hasErrors()) {
throw new CustomException(result);
}
} else if (parameter.equals("Y")) {
ClassB classB = mapper.convertValue(request, ClassB.class);
classBValidator.validate(classB, result);
if(result.hasErrors()) {
throw new CustomException(result);
}
} else {
// ..
}
return ResponseEntity.ok("Ok");
}
}
I think this one is a simpler solution:
#RestController
#RequestMapping("/my-custom-url")
public class MyController {
#PostMapping("/param1")
public ResponseEntity<Object> handleClassA(
#Valid #RequestBody ClassA classA,
BindingResult result) {
...
return ResponseEntity.ok("Ok");
}
#PostMapping("/param2")
public ResponseEntity<Object> handleClassB(
#Valid #RequestBody ClassB classB,
BindingResult result) {
...
return ResponseEntity.ok("Ok");
}
}
I am not sure why above answers explaining validators. as I understand you are trying to return two type of responses based on condition. that is not possible. because return type validate on compile time. so if you set return type as classA you must return classA. you cannot return classB. (unless classB is a classA relationship) so if you really want to do this you can use name interface to enforce the type.
#GetMapping(value = "/{id}")
public Response getRent(#PathVariable int id, #RequestParam(required = false) String type) {
if(type=="A"){
return new ClassA(rentService.findById(id));
}else{
return new ClassB (rentService.findDetailResponse(id));
}
}
P.S: you may need to return this as
public ResponseEntiry<Response>
but I just used Response directly.
now you need to create those two classes from same interface
public interface Response {
}
public class ClassA implements Response {
// your code goes here
}
public class ClassB implements Response {
// code here
}
this way you can achieve what you are trying.
I have created an API with a Map<String, Integer> parameter, like this:
#RequestMapping(value = "upload", method = RequestMethod.POST)
public ResponseEntity<String> handleContactsFileUpload(#RequestParam("file") MultipartFile file,
#RequestParam("name") String name,
#RequestParam("campaignAppItemId") Long campaignAppItemId,
#RequestParam("fileColumnHeaders") Map<String,Integer> fileColumnHeaders) throws Exception {
if (file == null)
return new ResponseEntity<>("No file uploaded", HttpStatus.BAD_REQUEST);
contactService.handleContactsFile(file, name, campaignAppItemId,fileColumnHeaders);
return new ResponseEntity<>("File uploaded successfully", HttpStatus.OK);
}
I am trying to call this via Postman:
I passed the fileColumnHeaders inside Body->Form Data as in the screenshot.
Then I got a message like this in Postman:
Failed to convert value of type 'java.lang.String' to required type 'java.util.Map'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'java.util.Map': no matching editors or conversion strategy found.
Anybody know why this message came ?
How can we pass a map as a parameter in Rest API request?
How can we pass a map through Postman?
You could use #RequestBody instead of #RequestParam for Maps and other non trivial data types and objects - this way spring will map the JSON representing your map parameter to a domain object, which is then serializable and can be converted to a java object.
... Or simply create a converter:
#Component
#RequiredArgsConstructor
public class StringToMapConverter implements Converter<String, Map<String, Object>> {
private final ObjectMapper objectMapper;
#Override
public Map<String, Object> convert(String source) {
try {
return objectMapper.readValue(source, new TypeReference<Map<String, String>>() {
});
} catch (final IOException e) {
return null;
}
}
}
Firstly, you create DTO object to get all data from your request.
public class FormDataDTO {
private MultipartFile file;
private String name;
private Long campaignAppItemId;
private Map<String,Integer> fileColumnHeaders;
// getters, setters
}
Secondly, you can map FormDataDTO from your request without any annotation:
#RequestMapping(value = "upload", method = RequestMethod.POST)
public ResponseEntity<String> handleContactsFileUpload(FormDataDTO formDataDTO){
// your logic code here
}
Finally, form-data in your request will be:
I think this could work:
#RequestMapping(value = "upload/{fileColumnHeaders}", method = RequestMethod.POST)
public ResponseEntity<String> handleContactsFileUpload(#RequestParam("file") MultipartFile file,
#RequestParam("name") String name,
#RequestParam("campaignAppItemId") Long campaignAppItemId,
#MatrixVariable Map<String,Integer> fileColumnHeaders) throws Exception {
if (file == null)
return new ResponseEntity<>("No file uploaded", HttpStatus.BAD_REQUEST);
contactService.handleContactsFile(file, name, campaignAppItemId,fileColumnHeaders);
return new ResponseEntity<>("File uploaded successfully", HttpStatus.OK);
}
Put all other parameters into the body, but add the fileColumnHeaders to the URL like this:
/upload/firstName=1;lastName=2;address=3;phone=4
You will also need this extra configuration:
#Configuration
public class WebConfig implements WebMvcConfigurer {
#Override
public void configurePathMatch(PathMatchConfigurer configurer) {
UrlPathHelper urlPathHelper = new UrlPathHelper();
urlPathHelper.setRemoveSemicolonContent(false);
configurer.setUrlPathHelper(urlPathHelper);
}
}
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 need to filter some attribute only in one controller.
Fasterxml JsonFilter works when I used it with ObjectMapper in the controller as follow
FilterProvider filter2 = new SimpleFilterProvider().addFilter("somefilter",
SimpleBeanPropertyFilter.filterOutAllExcept("prop1","prop2"));
With object like
#JsonFilter("somefilter")
public class Bar{
String prop1;
String prop2;
String prop3;
}
But when trying to return the same object with spring controller
#RequestMapping(value = "/path", method = RequestMethod.GET)
protected #ResponseBody Foo handleGet( ..
where
public class Foo{
Bar p1;
Bar p2;
}
the Bar attribute are omitted completely. In this case we need to return the Object unfiltered.
I have to use the object mapper in the controller to return the whole object.
Is there a way to disable the filter for the controller ?
You can try MappingJacksonValue to set Jackson filter provider to serialize the POJO with in Spring controller.
From the source code of AbstractJackson2HttpMessageConverter:
protected void writeInternal(Object object, Type type, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
...
try {
...
if (object instanceof MappingJacksonValue) {
MappingJacksonValue container = (MappingJacksonValue) object;
...
filters = container.getFilters();
}
...
ObjectWriter objectWriter;
if (serializationView != null) {
objectWriter = this.objectMapper.writerWithView(serializationView);
}
else if (filters != null) {
objectWriter = this.objectMapper.writer(filters);
}
else {
objectWriter = this.objectMapper.writer();
}
...
objectWriter.writeValue(generator, value);
...
}
It should be possible to reset the FilterProvider in objectMapper by filters set in MappingJacksonValue. In your case, you can try something like follows:
#RequestMapping(value = "/foo", method = RequestMethod.GET)
protected #ResponseBody MappingJacksonValue handleGet(...) {
MappingJacksonValue mappingJacksonValue = new MappingJacksonValue(foo);
FilterProvider filter = new SimpleFilterProvider().addFilter("somefilter", SimpleBeanPropertyFilter.serializeAllExcept());
mappingJacksonValue.setFilters(filter);
return mappingJacksonValue;
}
If you only have one controller require to filter out properties from Bar, you may also consider to add filter for the particular controller instead of setting it into the ObjectMapper:
#RequestMapping(value = "/bar", method = RequestMethod.GET)
protected #ResponseBody MappingJacksonValue handleGet(...) {
MappingJacksonValue mappingJacksonValue = new MappingJacksonValue(bar);
FilterProvider filter = new SimpleFilterProvider().addFilter("somefilter", SimpleBeanPropertyFilter.filterOutAllExcept("prop1","prop2"));
mappingJacksonValue.setFilters(filter);
return mappingJacksonValue;
}