Question 233209 in Json Question posted in
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Spring Boot controller to handle invalid JSON

I have a Spring Boot controller that consumes JSON:

    @PostMapping(
    value = "/shipdetails")
    public ResponseEntity acceptShip(@RequestBody Ship ship, HttpServletRequest request) {
        shipService.checkShip(ship);
        return new ResponseEntity<>(HttpStatus.OK);
    }

There is a corresponding Ship Entity:

public class Ship implements Serializable {

@JsonProperty("Name")
private String name;
@JsonProperty("Owner")
private String owner;

public Ship(String name, String owner) {
    this.name = name;
    this.owner = owner;    }

public Ship() {
}

// Getters and Setters removed for brevity

And finally the service:

@Service
public class ShipService {

Boolean checkShip(Ship ship) {
    if (ship.getName().equals("Queen Mary")) {
         // do something
    }
//edited for brevity

Sample invalid JSON:

{
    "name_wrong":"test name",
    "owner":"Lloyds Shipping"
}

Currently the error I get on the stacktrace if I send invalid JSON is (service layer) : Cannot invoke "String.equals(Object)" because the return value of "com.ships.Ship.getName()" is null.

Jackson needs the no-args constructor for de-serialization.

When inspecting in the debugger the Ship entity has a owner set, but not a name set, so its not the the whole entity is null – just one field.

I tried my Ship entity without a default no args constructor so you could not even pass entity with a null field to the service but then it fails with even valid JSON.

How and where should the exception for invalid JSON be handled?

Tags:

2

Answers


  1. 0

    Rather than viewing the issue as being a misnamed field, think of it as instead being two issues: a missing property (name) and an extra property (name_wrong).

    Spring Boot is configured by default to ignore any extra properties. And unless you tell the controller that the name property is required (e.g. by using the @NotNull bean validation annotation on the name field), it will happily accept a null value for this property.

    Missing required property

    The NullPointerException is happening since you’re attempting to call equals on the null name field.

    ship.getName().equals("Queen Mary")
^^^^^^^^^^^^^^

    There are a few different fixes for this. First, you could add a bean validation to the required fields:

    public class Ship implements Serializable {
  @NotNull
  @JsonProperty("Name")
  private String name;

  @JsonProperty("Owner")
  private String owner;

  // ...
}

    Alternatively, you could change the equals method to be null-safe:

    Boolean checkShip(Ship ship) {
    if (Objects.equals(ship.getName(), "Queen Mary"))) {
         // do something
    }
}

    Extra property

    There are several ways to have Spring reject the extra name_wrong property.

    If you want the application to always reject unknown properties (unless a particular bean opts out of it), you can configure it globally:

    application.yml

    spring.jackson.deserialization.fail-on-unknown-properties: false
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  2. 0

    Need to add few annotations and checks for the validation of the request body json.

    1. Add dependency in pom.xml for the below annotations-

    <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
            <version>3.1.1</version>
</dependency>

    2. @Valid with Request Body

        @PostMapping(value = "/shipdetails")
    public ResponseEntity acceptShip(@Valid @RequestBody Ship ship, 
                                     HttpServletRequest request)

    3. @NotNull with the mandatory attributes

        public class Ship implements Serializable {

      @NotNull(message = "The name is mandatory")
      @JsonProperty("Name")
      private String name;
      @JsonProperty("Owner")
      private String owner;

    4. Additional null check before equals method

    Boolean checkShip(Ship ship) {
        if (StringUtils.isNotBlank(ship.getName()) 
            && ship.getName().equals("Queen Mary")) {
            // do something
        }

    Output with Invalid json:

    Input

        {
     "name_wrong":"test name",
     "owner":"Lloyds Shipping"
    }

    Output:
    You will get a 400 Bad request status with the long error stack trace includes something like this

        "message": "Validation failed for object='ship'. Error count: 1",
"errors": [
    {
        "codes": [
            "NotNull.ship.name",
            "NotNull.name",
            "NotNull.java.lang.String",
            "NotNull"
        ],
        "arguments": [
            {
                "codes": [
                    "ship.name",
                    "name"
                ],
                "arguments": null,
                "defaultMessage": "name",
                "code": "name"
            }
        ],
        "defaultMessage": "The name is mandatory",
        "objectName": "ship",
        "field": "name",
        "rejectedValue": null,
        "bindingFailure": false,
        "code": "NotNull"
    }
]
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