One of my highest voted posts on Stack Overflow is an answer to Deserialize enum ignoring case in Spring Boot controller question. Frankly, the answer is incorrect. The whole situation is puzzling since I don’t get why it was upvoted.
Enum constants are case sensitive
Consider the following enum and corresponding @RestController:
public enum ExampleEnum {
FIRST,
SECOND
}
@RestController
public class ExampleEnumController {
@GetMapping("/enum")
public ExampleEnum getByName(@RequestParam(name = "name", required = false) ExampleEnum ee) {
return ee;
}
}
This will work as intended and return 200 response when name request parameter value is uppercase e.g. GET http://localhost:8080/enum?mame=FIRST. However, when name value is lowercase e.g. GET http://localhost:8080/enum?mame=first the code will return a 400 response:
{
"timestamp": "2020-03-28T10:21:20.989+0000",
"status": 400,
"error": "Bad Request",
"message": "Failed to convert value of type 'java.lang.String' to required type 'kad.ExampleEnum'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [@org.springframework.web.bind.annotation.RequestParam kad.ExampleEnum] for value 'first'; nested exception is java.lang.IllegalArgumentException: No enum constant kad.ExampleEnum.first",
"path": "/enum"
}
Custom case-insensitive matching
The default behaviour is caused by Spring utilizing com.sun.beans.editors.EnumEditor to map enum values mapped with @RequestParam annotation. To change this we have to declare our own editor.
import java.beans.PropertyEditorSupport;
public class CaseInsensitiveEnumEditor extends PropertyEditorSupport {
private final Class<? extends Enum> enumType;
private final String[] enumNames;
public CaseInsensitiveEnumEditor(Class<?> type) {
this.enumType = type.asSubclass(Enum.class);
var values = type.getEnumConstants();
if (values == null) {
throw new IllegalArgumentException("Unsupported " + type);
}
this.enumNames = new String[values.length];
for (int i = 0; i < values.length; i++) {
this.enumNames[i] = ((Enum<?>) values[i]).name();
}
}
@Override
public void setAsText(String text) throws IllegalArgumentException {
if (text == null || text.isEmpty()) {
setValue(null);
return;
}
for (String n : enumNames) {
if (n.equalsIgnoreCase(text)) {
@SuppressWarnings("unchecked")
var newValue = Enum.valueOf(enumType, n);
setValue(newValue);
return;
}
}
throw new IllegalArgumentException("No enum constant " + enumType.getCanonicalName() + " equals ignore case " + text);
}
}
Now we have to register the new editor with @InitBinder:
@RestController
public class ExampleEnumController {
@GetMapping("/enum")
public ExampleEnum getByName(@RequestParam(name = "name", required = false) ExampleEnum ee) {
return ee;
}
@InitBinder
public void initBinder(WebDataBinder binder) {
binder.registerCustomEditor(ExampleEnum.class, new CaseInsensitiveEnumEditor(ExampleEnum.class));
}
}