First off my question is very similar to below however I'm not sure if the answers are applicable to my specific problem or whether I just need clarification about how to approach it:
Convert LinkedHashMap<String,String> to an object in Java
I am using struts2 json rest plugin to convert a json array into a java array. The array is sent through an ajax post request and the java receives this data. However instead of being the object type I expect it is received as a LinkedHashmap. Which is identical to the json request in structure.
[
{advance_Or_Premium=10000, available=true},
{advance_Or_Premium=10000, available=true},
{advance_Or_Premium=10000, available=true}
]
The data is all present and correct but just in the wrong type. Ideally I want to send the data in my object type or if this is not possible convert the LinkedHashMap from a list of keys and values into the object array. Here is the class I am using, incoming data is received in the create() method:
#Namespace(value = "/rest")
public class OptionRequestAction extends MadeAbstractAction implements ModelDriven<ArrayList<OptionRequestRest>>
{
private String id;
ArrayList<OptionRequestRest> model = new ArrayList<OptionRequestRest>();
public HttpHeaders create()
{
// TODO - need to use model here but it's a LinkedHashmap
return new DefaultHttpHeaders("create");
}
public String getId()
{
return this.id;
}
public ArrayList<OptionRequestRest> getModel()
{
return this.model;
}
public ArrayList<OptionRequestRest> getOptionRequests()
{
#SuppressWarnings("unchecked")
ArrayList<OptionRequestRest> lReturn = (ArrayList<OptionRequestRest>) this.getSession().get("optionRequest");
return lReturn;
}
// Handles /option-request GET requests
public HttpHeaders index()
{
this.model = this.getOptionRequests();
return new DefaultHttpHeaders("index").lastModified(new Date());
}
public void setId(String pId)
{
this.id = pId;
}
public void setModel(ArrayList<OptionRequestRest> pModel)
{
this.model = pModel;
}
// Handles /option-request/{id} GET requests
public HttpHeaders show()
{
this.model = this.getOptionRequests();
return new DefaultHttpHeaders("show").lastModified(new Date());
}
}
One of the things which is confusing me is that this code works fine and returns the correct object type if the model is not an array. Please let me know if my question is not clear enough and needs additional information. Thanks.
Related
I want to retrieve all the skills form the skills entity in postgresql and send it using get method to the Angular front end.In HTTP request I need to send a JSON object.How can I convert the retrieved values from the postgresql to a JSON object?
I have connected the postgresql db using spring JPA. And also I get a string values to my front end. But I wanted those as JSON object
This is my controller class
#RestController
#CrossOrigin
public class SkillsController {
#Autowired
SkillsRepository skillsRepository;
#RequestMapping("/getSkills")
#GetMapping("/getSkills")
#CrossOrigin
public String getSkills(){
String result = "";
for (Skills skill : skillsRepository.findAll()){
result += skill.toString();
}
return result;
}
This is my Angular front end ts file
public getAllSkills() {
const url = 'http://localhost:8080/getSkills';
this.http.get(url, {responseType: 'text'}).subscribe(
res => {
alert(res);
},
err => {
alert('Error in retrieving');
}
);
}
I want to convert my retrieved valus in to JSON object and catch that object using get method in the front end
Spring uses Jackson serialization/deserialization by default and also the return type is Json. Instead of returning a String return type, return the object itself and it will be converted into Json without any additional code from your end. You controller would typically look as specified below.
#RestController
#CrossOrigin
public class SkillsController {
#Autowired
SkillsRepository skillsRepository;
#GetMapping("/getSkills")
public List<Skill> getSkills() {
return skillsRepository.findAll();
}
}
I will be doing some rewrite to your post. so the answer is pretty straight forward, you can simply return list from the repository and Spring will convert the list to the appriopriate JSON object or array.
#CrossOrigin
public class SkillsController {
public SkillsRepository skillsRepository;
public SkillsController(SkillsRepository _skillsRepository){
skillsRepository = _skillsRepository;
}
#RequestMapping("/getSkills")
#CrossOrigin
public List<skillEntity> getSkills(){
return (List<skillEntity>)skillsRepository.findAll();
}
}
I have an application where I have an html page which takes user input through a textbox.This is a REST Spring Framework and is divided as Controller, Entity, Service, Repository, View and the main application class.
I take an input value and search in the Mongodb database, If the value is present, I return the entity object from Service to Controller. The controller returns the same Entity View object.- PersonView in this case. I get a JSON Data.
The above scenario works well as long as there are records in the database. In case if the record is not present, it returns an empty JSON. My Controller returns Person View Object and I do not wish to change the signature and make the return type as String since in that case it returns the address on my HTML page.
Considering this, how should I handle the case when there are no records in the database and I wish to display a message on this same HTML page saying there are no records available.
I tried throwing an exception but in this case too, how Do I display message on my HTML considering that my Controller returns JSON object and I do not wish to change its signature?
Controller Class is as below:
public PersonView searchPerson(#PathVariable String pname) {
List<Person> pList= PersonService.searchPerson(pname);
PersonView personView = new PersonView();
personView.setPersonView(pList);
return personView;
EDIT:
Here is the function from personView Class that I call in Controller:
public List<Person> setPersonView() {
this.personView = personView;
}
Here is the service Impl class:
public List<Person> searchPerson(String name) throws Exception {
List<Person> personlist= new ArrayList<Person>();
personlist = personRepository.findByName(name);
if (personlist.isEmpty())
throw new Exception("Records not found in the the database");
return personlist;
}
Create a custom Exception class:
public class EntityNotFoundException extends RuntimeException {
public EntityNotFoundException(String message) {
super(message);
}
}
Now, in you controller code:
public List<Person> searchPerson(String name) {
List<Person> personlist= new ArrayList<Person>();
personlist = personRepository.findByName(name);
if (personlist.isEmpty()) {
throw new EntityNotFoundException("Records not found in the the database");
}
return personlist;
}
After that you can try something like this in you controller class:
private static final MappingJacksonJsonView JSON_VIEW = new MappingJacksonJsonView();
#ExceptionHandler(EntityNotFoundException.class)
public ModelAndView handleNotFoundException( Exception ex )
{
return new ModelAndView(JSON_VIEW, "error", new ErrorMessage("No Record in Db") );
}
Your ErrorMessage class can be a simple POJO:
public class ErrorMessage {
private String message;
ErrorMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
Although already answered, I will add some points here.
Please note that at some point of time you will have a requirement to send the
headers, Response body (with different Objects). So consider using ResponseEntity Object which will be a wrapper to your List. Here is the sample code.
public ResponseEntity<List<Person>> searchPerson(String name) {
List<Person> personlist= new ArrayList<Person>();
personlist = personRepository.findByName(name);
if (personlist.isEmpty()) {
return new ResponseEntity(new EntityNotFoundException("Records not found in the the database"), HttpStatus.BAD_REQUEST);
}
return new ResponseEntity(personlist , HttpStatus.OK);
}
Response Entity Object provides flexibility to greater extent. Read the documentation here.
https://docs.spring.io/spring/docs/current/javadocapi/org/springframework/http/ResponseEntity.html
I need to replace the DateTime serialization for JSON in WCF REST Self Hosted service. Right now, I'm using something like the following code to do it, but it's definitely not the way to go since it requires manipulating each class.
[DataContract]
public class Test
{
[IgnoreDataMember]
public DateTime StartDate;
[DataMember(Name = "StartDate")]
public string StartDateStr
{
get { return DateUtil.DateToStr(StartDate); }
set { StartDate = DateTime.Parse(value); }
}
}
where my utility function DateUtil.DateToStr does all the formatting work.
Is there any easy way to do it without having to touch the attributes on my classes which have the DataContract attribute? Ideally, there would be no attributes, but a couple of lines of code in my configuration to replace the serializer with one where I've overridden DateTime serialization.
Everything that I've found looks like I have to replace huge pieces of the pipeline.
This article doesn't appear to apply because in I'm using WebServiceHost not HttpServiceHost, which not part of the 4.5.1 Framework.
JSON.NET Serializer for WCF REST Services
By default WCF uses DataContractJsonSerializer to serialize data into JSON. Unfortunatelly date from this serializer is in very difficult format to parse by human brain.
"DateTime": "\/Date(1535481994306+0200)\/"
To override this behavior we need to write custom IDispatchMessageFormatter. This class will receive all data which should be returned to requester and change it according to our needs.
To make it happen to the operations in the endpoint add custom formatter - ClientJsonDateFormatter:
ServiceHost host=new ServiceHost(typeof(CustomService));
host.AddServiceEndpoint(typeof(ICustomContract), new WebHttpBinding(), Consts.WebHttpAddress);
foreach (var endpoint in host.Description.Endpoints)
{
if (endpoint.Address.Uri.Scheme.StartsWith("http"))
{
foreach (var operation in endpoint.Contract.Operations)
{
operation.OperationBehaviors.Add(new ClientJsonDateFormatter());
}
endpoint.Behaviors.Add(new WebHttpBehavior());
}
}
ClientJsonDateFormatter is simple class which just applies formatter ClientJsonDateFormatter
public class ClientJsonDateFormatter : IOperationBehavior
{
public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters) { }
public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation) { }
public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
{
dispatchOperation.Formatter = new ResponseJsonFormatter(operationDescription);
}
public void Validate(OperationDescription operationDescription) { }
}
In the formatter we took imput and serialize it with the changed Serializer:
public class ResponseJsonFormatter : IDispatchMessageFormatter
{
OperationDescription Operation;
public ResponseJsonFormatter(OperationDescription operation)
{
this.Operation = operation;
}
public void DeserializeRequest(Message message, object[] parameters)
{
}
public Message SerializeReply(MessageVersion messageVersion, object[] parameters, object result)
{
string json=Newtonsoft.Json.JsonConvert.SerializeObject(result);
byte[] bytes = Encoding.UTF8.GetBytes(json);
Message replyMessage = Message.CreateMessage(messageVersion, Operation.Messages[1].Action, new RawDataWriter(bytes));
replyMessage.Properties.Add(WebBodyFormatMessageProperty.Name, new WebBodyFormatMessageProperty(WebContentFormat.Raw));
return replyMessage;
}
}
And to send information to client we need data writer - RawDataWriter. Its implementation is simple:
class RawDataWriter : BodyWriter
{
byte[] data;
public RawDataWriter(byte[] data)
: base(true)
{
this.data = data;
}
protected override void OnWriteBodyContents(XmlDictionaryWriter writer)
{
writer.WriteStartElement("Binary");
writer.WriteBase64(data, 0, data.Length);
writer.WriteEndElement();
}
}
Applying all code will result in returning date in more friendly format:
"DateTime":"2018-08-28T20:56:48.6411976+02:00"
To show it in practice I created example in the github branch DateTimeFormatter.
Please check also this answer as very likely you also will need it.
There is a limitation in JSON to convert DateTime, specially according to your case.
Please see http://msdn.microsoft.com/en-us/library/bb412170(v=vs.110).aspx
and read the section Dates/Times and JSON
To resolve this problem, I simply changed the type of serialization from JSON to XML for all the calls including DateTime.
After long time discussion ,I have find out the solution for it.
Please Use the following Code to Solve serialized date..
[IgnoreDataMember]
public DateTime? PerformanceDate { get; set; }
[DataMember(EmitDefaultValue = false, Name = "PerformanceDate")]
public string UpdateStartDateStr
{
get
{
if (this.PerformanceDate.HasValue)
return this.PerformanceDate.Value.ToUniversalTime().ToString("s", CultureInfo.InvariantCulture);
else
return null;
}
set
{
// should implement this...
}
}
What I want to do:
An user is prompted with a list of choices of actions to take, for example, Search User, Register New User, and so on. My idea is that when an user click pick one of the choices, an AJAX call is triggered using JQuery and then the method is executed, returning a JSONResponse.
A JSONResponse is just a simple object with 2 variables: status as String, and result as Object, as following:
public class JSONResponse {
private String status = null;
private Object result = null;
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public Object getResult() {
return result;
}
public void setResult(Object result) {
this.result = result;
}
}
However, sometimes I want to return a ModelAndView into this response. For example: when the user search for a user, the application searches for it and then return a ModelAndView with a list of possible users. One way to achieve this is to render a ModelAndView as String and then put it as result into a JSONResponse object. The problem is that how can I render a ModelAndView as String to put it into the JSONReponse?
PS: I'm using Tomcat 7, JDK 6, Spring MVC 3.0 with Tiles 2, Jackson (to convert java objects to JSON)
You can return ModelAndView if needed else write to a response stream.
public ModelAndView getSomething(HttpServletResponse response) {
// perform your logic
if(obj returned must be a json) {
try {
new MappingJacksonHttpMessageConverter().write(obj, MediaType.APPLICATION_JSON, new ServletServerHttpResponse(response));
} catch(Exception e) {
logger.error("Error while serializing to JSON string.");
}
return null;
} else {
return new ModelAndView("yourview");
}
}
From your question what I understand is sometimes you need to return json and sometimes model and view because you are passing search list using model and view.
Ideally these two things must be handled in different method but as you want to handle it in same method then your method must return String instead of ModelAndView so that you can return json data. And search list which you want to send you can put it into session and then you will get it on JSP page (because of Session Scope).
Method will look somewhat like this :
public #ResponseBody
String methodName(HttpServletRequest request) {
if(jsondata){ //Wants to send json data
return jsonFinalData.toString();
}else{
//store search list in session
return view_name;
}
I'm working on a little app and using GWT to build it.
I just tried making a request to a remote server which will return a response as JSON.
I've tried using the overlay types concept but I couldn't get it working. I've been changing the code around so its a bit off from where the Google GWT tutorials left.
JavaScriptObject json;
public JavaScriptObject executeQuery(String query) {
String url = "http://api.domain.com?client_id=xxxx&query=";
RequestBuilder builder = new RequestBuilder(RequestBuilder.GET,
URL.encode(url + query));
try {
#SuppressWarnings("unused")
Request request = builder.sendRequest(null, new RequestCallback() {
public void onError(Request request, Throwable exception) {
// violation, etc.)
}
public void onResponseReceived(Request request,
Response response) {
if (200 == response.getStatusCode()) {
// Process the response in response.getText()
json =parseJson(response.getText());
} else {
}
}
});
} catch (RequestException e) {
// Couldn't connect to server
}
return json;
}
public static native JavaScriptObject parseJson(String jsonStr) /*-{
return eval(jsonStr );
;
}-*/;
In the chrome's debugger I get umbrellaexception, unable to see the stack trace and GWT debugger dies with NoSuchMethodError... Any ideas, pointers?
You may have a look to GWT AutoBean framework.
AutoBean allow you to serialize and deserialize JSON string from and to Plain Old Java Object.
For me this framework became essential :
Code is cleaner than with JSNI objects (JavaScript Native Interface)
No dependancy with Framework not supported by Google (like RestyGWT)
You just define interfaces with getters and setters :
// Declare any bean-like interface with matching getters and setters,
// no base type is necessary
interface Person {
Address getAddress();
String getName();
void setName(String name):
void setAddress(Address a);
}
interface Address {
String getZipcode();
void setZipcode(String zipCode);
}
Later you can serialize or deserialize JSON String using a factory (See documentation) :
// (...)
String serializeToJson(Person person) {
// Retrieve the AutoBean controller
AutoBean<Person> bean = AutoBeanUtils.getAutoBean(person);
return AutoBeanCodex.encode(bean).getPayload();
}
Person deserializeFromJson(String json) {
AutoBean<Person> bean = AutoBeanCodex.decode(myFactory, Person.class, json);
return bean.as();
}
// (...)
First post on Stack Overflow (!) : I hope this help :)
Use JsonUtils#safeEval() to evaluate the JSON string instead of calling eval() directly.
More importantly, don't try to pass the result of an asynchronous call (like RequestBuilder#sendRequest() back to a caller using return - use a callback:
public void executeQuery(String query,
final AsyncCallback<JavaScriptObject> callback)
{
...
try {
builder.sendRequest(null, new RequestCallback() {
public void onError(Request request, Throwable caught) {
callback.onFailure(caught);
}
public void onResponseReceived(Request request, Response response) {
if (Response.SC_OK == response.getStatusCode()) {
try {
callback.onSuccess(JsonUtils.safeEval(response.getText()));
} catch (IllegalArgumentException iax) {
callback.onFailure(iax);
}
} else {
// Better to use a typed exception here to indicate the specific
// cause of the failure.
callback.onFailure(new Exception("Bad return code."));
}
}
});
} catch (RequestException e) {
callback.onFailure(e);
}
}
Generally, the workflow you're describing consists of four steps:
Make the request
Receive the JSON text
Parse the JSON in JavaScript objects
Describe these JavaScript objects using an overlay type
It sounds like you've already got steps 1 and 2 working properly.
Parse the JSON
JSONParser.parseStrict will do nicely. You'll be returned a JSONValue object.
This will allow you to avoid using your custom native method and will also make sure that it prevents arbitrary code execution while parsing the JSON. If your JSON payload is trusted and you want raw speed, use JSONParser.parseLenient. In either case, you need not write your own parser method.
Let's say that you're expecting the following JSON:
{
"name": "Bob Jones",
"occupations": [
"Igloo renovations contractor",
"Cesium clock cleaner"
]
}
Since you know that the JSON describes an object, you can tell the JSONValue that you're expecting to get a JavaScriptObject.
String jsonText = makeRequestAndGetJsonText(); // assume you've already made request
JSONValue jsonValue = JSONParser.parseStrict(jsonText);
JSONObject jsonObject = jsonValue.isObject(); // assert that this is an object
if (jsonObject == null) {
// uh oh, it wasn't an object after
// do error handling here
throw new RuntimeException("JSON payload did not describe an object");
}
Describe as an overlay type
Now that you know that your JSON describes an object, you can get that object and describe it in terms of a JavaScript class. Say you have this overlay type:
class Person {
String getName() /*-{
return this.name;
}-*/;
JsArray getOccupations() /*-{
return this.occupations;
}-*/;
}
You can make your new JavaScript object conform to this Java class by doing a cast:
Person person = jsonObject.getJavaScriptObject().cast();
String name = person.getName(); // name is "Bob Jones"
Using eval is generally dangerous, and can result in all kinds of strange behavior, if the server returns invalid JSON (note, that it's necessary, that the JSON top element is an array, if you simply use eval(jsonStr)!). So I'd make the server return a very simple result like
[ "hello" ]
and see, if the error still occurs, or if you can get a better stack trace.
Note: I assume, that the server is reachable under the same URL + port + protocol as your GWT host page (otherwise, RequestBuilder wouldn't work anyway due to Same Origin Policy.)
You actually don't need to parse the JSON, you can use native JSNI objects (JavaScript Native Interface).
Here's an example I pulled from a recent project doing basically the same thing you're doing:
public class Person extends JavaScriptObject{
// Overlay types always have protected, zero argument constructors.
protected Person(){}
// JSNI methods to get stock data
public final native String getName() /*-{ return this.name; }-*/;
public final native String getOccupation() /*-{ return this.occupation; }-*/;
// Non-JSNI methods below
}
and then to retrieve it like so:
/**
* Convert the string of JSON into JavaScript object.
*
*/
private final native JsArray<Person> asArrayOfPollData(String json) /*-{
return eval(json);
}-*/;
private void retrievePeopleList(){
errorMsgLabel.setVisible(false);
String url = JSON_URL;
url = URL.encode(url);
RequestBuilder builder = new RequestBuilder(RequestBuilder.POST, url);
try{
#SuppressWarnings("unused")
Request request = builder.sendRequest(null, new RequestCallback() {
#Override
public void onResponseReceived(Request req, Response resp) {
if(resp.getStatusCode() == 200){
JsArray<Person> jsonPeople = asArrayOfPeopleData(resp.getText());
populatePeopleTable(people);
}
else{
displayError("Couldn't retrieve JSON (" + resp.getStatusText() + ")");
}
}
#Override
public void onError(Request req, Throwable arg1) {
System.out.println("couldn't retrieve JSON");
displayError("Couldn't retrieve JSON");
}
});
} catch(RequestException e) {
System.out.println("couldn't retrieve JSON");
displayError("Couldn't retrieve JSON");
}
}
So essentially you're casting the response as an array of JSON Objects. Good stuff.
More info here: http://code.google.com/webtoolkit/doc/latest/DevGuideCodingBasicsJSNI.html