Why I can't Receive String and It's null - spring-mvc

Question

#RequestMapping(value = "/save",method = RequestMethod.POST)
#ResponseStatus(value= HttpStatus.OK)
public void save(String str) throws IOException {
System.out.println(str);
}
all I got is null:

Answer 1

You need to tell Spring where to get str from.
If you're sending the JSON
{ "str": "sasfasfafa" }
You'll need a class that deserialises from this and annotate the method parameter with #RequestBody.
public class StrEntity {
private String str;
public String getStr() {
return str;
}
public void setStr(String str) {
this.str = str;
}
}
public class MyController {
#RequestMapping(value = "/save",method = RequestMethod.POST)
#ResponseStatus(value= HttpStatus.OK)
public void save(#RequestBody StrEntity entity) throws IOException {
System.out.println(entity.getStr());
}
}
If you just want to send a string as the request body (i.e. sasfasfafa) instead of the JSON document you can do this:
public class MyController {
#RequestMapping(value = "/save",method = RequestMethod.POST)
#ResponseStatus(value= HttpStatus.OK)
public void save(#RequestBody String str) throws IOException {
System.out.println(str);
}
}
There is no way to send the JSON { "str": "sasfasfafa" } as request body and only have a String as a method parameter in the controller.

Answer 2

Use #RequestParam annotation to get the parameter.
#RequestMapping(value = "/save",method = RequestMethod.POST)
#ResponseStatus(value= HttpStatus.OK)
public void save(#RequestParam(name="str") String str) throws IOException {
System.out.println(str);
}