I am trying to build a Spring MVC controller which will receive a POSTed form with a parameter in JSON format, and have Spring automatically convert it to a Java object.
Request content type is application/x-www-form-urlencoded
The name of the parameter that contains a JSON string is data.json
This is the controller:
#Controller
public class MyController {
#RequestMapping(value = "/formHandler", method = RequestMethod.POST)
public #ResponseBody String handleSubscription(
#RequestParam("data.json") MyMessage msg) {
logger.debug("id: " + msg.getId());
return "OK";
}
}
And this is what the MyMessage object looks like:
public class MyMessage {
private String id;
// Getter/setter omitted for brevity
}
Perhaps not surprisingly, posting a form with parameter data.json={"id":"Hello"} results in HTTP error 500 with this exception:
org.springframework.beans.ConversionNotSupportedException:
Failed to convert value of type 'java.lang.String' to required type 'MyMessage'
nested exception is java.lang.IllegalStateException:
Cannot convert value of type [java.lang.String] to required type [MyMessage]: no matching editors or conversion strategy found
If I read the MappingJackson2HttpMessageConverter docs correctly, Jackson JSON conversion is triggered by Content-Type application/json, which I obviously cannot use since this is a form POST (and I don't control the POSTing part).
Is it possible to get Spring to convert the JSON string into an instance of MyMessage, or should I just give up, read it as a String and perform the conversion myself?
Spring invokes your #RequestMapping methods with reflection. To resolve each argument it's going to pass to the invocation, it uses implementations of HandlerMethodArgumentResolver. For #RequestParam annotated parameters, it uses RequestParamMethodArgumentResolver. This implementation binds a request parameter to a single object, typically a String or some Number type.
However, your use case is a little more rare. You rarely receive json as a request parameter, which is why I think you should re-think your design, but if you have no other choice, you need to register a custom PropertyEditor that will take care of converting the request parameter's json value into your custom type.
Registration is simple in an #InitBinder annotated method in your #Controller class
#InitBinder
public void initBinder(WebDataBinder dataBinder) {
dataBinder.registerCustomEditor(MyMessage.class, new PropertyEditorSupport() {
Object value;
#Override
public Object getValue() {
return value;
}
#Override
public void setAsText(String text) throws IllegalArgumentException {
value = new Gson().fromJson((String) text, MyMessage.class);
}
});
}
In this particular case, we don't need all the methods of the PropertyEditor interface, so we can use PropertyEditorSupport which is a helpful default implementation of PropertyEditor. We simply implement the two methods we care about using whichever flavor of JSON parser we want. I used Gson because it was available.
When Spring sees that it has a request parameter that you requested, it will check the parameter type, find the type MyMessage and look for a registered PropertyEditor for that type. It will find it because we registered it and it it will then use it to convert the value.
You might need to implement other methods of PropertyEditor depending on what you do next.
My recommendation is to never send JSON as a request parameter. Set your request content type to application/json and send the json as the body of the request. Then use #RequestBody to parse it.
You can also use #RequestPart like this:
#RequestMapping(value = "/issues", method = RequestMethod.POST, headers = "Content-Type=multipart/form-data")
public String uploadIssue(#RequestParam("image") MultipartFile file, #RequestPart("issue") MyMessage issue)
Related
I have a java class with uppercase field names and some of them with under scroll, like this:
public class DATADto {
private String UPPERCASE;
private String UNDER_SCROLL;
public String getUPPERCASE() { return UPPERCASE; }
public void setUPPERCASE(String s) { UPPERCASE = s; }
...//setters and getters
}
and I used this in a rest endpoint that accepts json in a spring rest controller:
#RestController
#RequestMapping({"/api/path"})
public class MyRestController {
#PostMapping(path = {"/Data"}, consumes = MediaType.APPLICATION_JSON_VALUE,
produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> useDATADto(#RequestBody DATADto aDATADto ) {
//do something
}
}
what JSON fields do I need to send by default and why?
The story goes like this..
Spring Boot by default uses Jackson ObjectMapper to serialize and deserialize Java objects.
In this context, by serialization we mean the conversion of java objects into json, deserialization is the reverse process.
Regarding the #RequestBody annotation, the following is written in the documentation:
Annotation indicating a method parameter should be bound to the body
of the web request. The body of the request is passed through an
HttpMessageConverter to resolve the method argument depending on the
content type of the request. Optionally, automatic validation can be
applied by annotating the argument with #Valid.
In short, #RequestBody annotation tells Spring to deserialize an incoming request body into an object passed as a parameter to the handler method. Spring achieves this using MessageConverter
Since Spring Boot uses Jackson by default for serializing and deserializing request and response objects in your REST APIs, and Jackson uses MappingJackson2HttpMessageConverter, so that will be message converter implementation that spring will use. You can read more about that here.
The important thing is that Jackson uses Java Bean naming conventions to figure out the json properties in a Java class. Acutally it uses default PropertyNamingStrategy . Here is what is written in documentation:
In absence of a registered custom strategy, default Java property
naming strategy is used, which leaves field names as is, and removes
set/get/is prefix from methods (as well as lower-cases initial
sequence of capitalized characters).
So, since you didn't set any naming strategy, it will use default one.
Beacause of that, if you send payload like this :
{
"uppercase": "YOUR_VALUE",
"under_scroll": "YOUR_VALUE"
}
That won't work, you will get exception, since there jackson won't find under_scroll property in your class, it will look for under_SCROLL , therefore this payload:
{
"uppercase": "YOUR_VALUE",
"under_SCROLL": "YOUR_VALUE"
}
will work.
To change default PropertyNamingStrategy check
this article.
It will depend on the Jackson property naming strategy. The default is LOWER_CAMEL_CASE , so your request body should look like this:
{
"uppercase": "test",
"under_scroll": "test"
}
For all possible configurations of the naming strategy for Jackson please refer to the document «Class PropertyNamingStrategy»
If you're using Spring, you may use this property to configure the naming strategy:
spring.jackson.property-naming-strategy
Another possible way will be the bean configuration:
#Bean
public Jackson2ObjectMapperBuilder jacksonBuilder() {
Jackson2ObjectMapperBuilder jacksonMapper = new Jackson2ObjectMapperBuilder();
jacksonMapper.propertyNamingStrategy(PropertyNamingStrategy.LOWER_CASE);
return jacksonMapper;
}
Additional note:
Your current naming approach doesn't follow the Java Code Conventions. If you need to process JSON with some specific naming format better to use the #JsonProperty annotation on the fields of your POJO.
Please see the example below:
import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.Data;
#Data
public class DATADto {
#JsonProperty("UPPERCASE")
private String uppercase;
#JsonProperty("UNDER_SCROLL")
private String underScroll;
}
You should send post request to /api/path/data with this request body:
{
"uppercase": "YOUR_VALUE",
"under_scroll": "YOUR_VALUE"
}
I want to validate the PathVariable of an endpoint. Actually, it's not a validation because it's done by the java itself. For example, if the PathVariable type is Integer and I pass String to it, it will throw something like this: Failed to convert value of type [java.lang.String] to required type [java.lang.Long]... - this it the response message. How can I set custom message (ex: The age must be a number)? I know that I can create a custom validator and use it with annotation but as I have many endpoints, I will have to create a really big amount of validators for every single PathVariable - looks like something is not OK because I know there must be a just easier way. Am I wrong?
You can create a handler for the MethodArgumentTypeMismatchException that is thrown:
#RestControllerAdvice
public class ExceptionControllerAdvice {
#Inject
private MessageSource messageSource;
#ExceptionHandler(MethodArgumentTypeMismatchException.class)
#ResponseStatus(HttpStatus.BAD_REQUEST)
public String handleTypeMismatch(MethodArgumentTypeMismatchException e) {
// Return custom message from messageSource using e.getRequiredType()
}
}
I would like to validate input of following #RequestMapping:
#RequestMapping(value = "/{id}", method = RequestMethod.GET)
#ResponseBody
public Response getCategory(#PathVariable("id") Long id) {
// some logic here
}
When consumer of the endpoint passes string following error occurs:
Failed to convert value of type [java.lang.String] to required type [java.lang.Long]; nested exception is java.lang.NumberFormatException: For input string: "null"
I could change it to string but I believe there is a better way to do it.
The answer from RC is a very good way to make sure your id will be made of digits.
In general if you want to validate incoming requests you could also create and register a custom interceptor by implementing HandlerInterceptor and then add your validation in the overridden preHandle method.
Controller signature (I have tried as requestbody as well) :
#RequestMapping(value = "/Lame", method = RequestMethod.POST)
public
#ResponseBody
boolean getLame(#RequestParam String strToMatchA, #RequestParam String strToMatchB) {}
And this as my json :
{
"strToMatchA": "EN",
"strToMatchB": "lon"
}
Not working, I receive the error :
org.springframework.web.bind.MissingServletRequestParameterException: Required String parameter 'strToMatchA' is not present
Removing this first parameter from method signature then makes it work (the method gets called correctly), what should I be doing ?
When I change method parameters to be annotated with #RequestBody I get the following error :
java.io.IOException: Stream closed
Your json is fine but not the controller signature.
Create a class with setters matching the json.
Use it as argument instead of your strings.
Annotate it with requestbody. It should work.
I have a method to which I want to post some json data, that looks like this
#RequestMapping(value = "/m1", method = RequestMethod.POST)
public Object m1(#RequestBody Map<String, ?> body) {
// do something
}
This works great when I set the content-type header to application/json when I post, but fails with an error if I don't (it cannot deserialize the post body into the map because it doesn't know how)
What would I have to configure in spring to make it use application/json as a default when no header is specified?
The class that converts the JSON to your object is called an HttpMessageConverter. I assume you are using the default Jackson one that comes with Spring. You can write a custom MessageConverter, that will always return true in it's supports method with your response object type and then just call the Jackson httpconverter in your readInternal and writeInternal methods. If you do this however, be careful, as once it's registered in your requesthandler, it will be asked on all #ResponseBody and #RequestBody requests.