如何用 Java 8 编写 instanceof？
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How to write instanceof with Java 8?
提问by Pracede
I am new in Java 8 Optional. I have to change the following code :
我是 Java 8 Optional 的新手。我必须更改以下代码：
@RequestMapping(value = "/account",
method = RequestMethod.GET,
produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<UserDTO> getAccount() {
return
Optional.ofNullable(userService.getUserWithAuthorities())
.map(user ->
new ResponseEntity<>(
new UserDTO(
user.getLogin(),
null,
user.getFirstName(),
user.getLastName(),
user.getEmail(),
"",
user.getLangKey(),
user.getAuthorities()
.stream()
.map(Authority::getName)
.collect(Collectors.toList())
),
HttpStatus.OK
)
)
.orElse(new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR));
}
I want to create a different ResponseEntity according to the instance of user.
How i can write the equivalent of the following code:
我想根据user. 我如何编写等效于以下代码的代码：
if(user instanceof Admin )
{
// my logic
}
else if(user instanceof NormalUser)
{
// my logic
}
Thanks
谢谢
回答by Tunaki
You would do it like this :
你会这样做：
@RequestMapping(value = "/account",
method = RequestMethod.GET,
produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<UserDTO> getAccount() {
return Optional.ofNullable(userService.getUserWithAuthorities())
.map(user -> {
if (user instanceof Admin) {
//...
}
return new ResponseEntity<>(new UserDTO(...), HttpStatus.OK);
})
.orElse(new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR));
}
However, if you can, avoid the instanceofoperator. Add a isAdminmethod to your Userclass : in class Admin, it would return trueand in class NormalUser, it would return false.
但是，如果可以，请避开instanceof运营商。isAdmin向您的User类添加一个方法：在类中Admin，它会返回，true而在类中NormalUser，它会返回false。
回答by bb94
The way you did it. However, you will have to cast uto the type you want.
你这样做的方式。但是，您必须强制u转换为您想要的类型。
if (u instanceof Admin) {
Admin a = (Admin) u;
// your logic
}
