Http 302
302是一个普通的重定向代码。直观的看来是,请求者(浏览器或者模拟http请求)发起一个请求,然后服务端重定向到另一个地址。而事实上,服务端仅仅是增加一条属性到header,location=重定向地址。而一般的,浏览器会自动的再去请求这个location,重新获取资源。也就是说,这个会使得浏览器发起两次请求。
Example
Client request:
GET /index.html HTTP/1.1
Host: www.example.com
Server response:
HTTP/1.1 302 Found
Location: http://www.iana.org/domains/example/
实验
- 首先,我们用一个Map来存储信息,key为username,value为随机数。
- 当我请求list的时候,跳转到users,来获取所有的用户。
Map<String, Double> users = new HashMap<>();
@RequestMapping(value = "/list", method = RequestMethod.GET)
public String index(){
return "redirect:/users";
}
@ResponseBody
@RequestMapping(value = "/users", method = RequestMethod.GET)
public ResponseEntity getUsers(){
ResponseEntity responseEntity = new ResponseEntity(users, HttpStatus.OK);
return responseEntity;
}
当时用浏览器访问的时候,会明显的看到浏览器地址变了,也就是说我明明请求的是list,结果你给我变成了users。然而,由于浏览器帮我们做了跳转的工作,我们感觉不出来,但从地址栏还是可以看到的。
查看
通过拦截请求可以看出来,访问了两次:
并且list是302,而users是200.也就是说list进行了重定向。再来看list的response:
Request URL:https://localhost:8443/list
Request Method:GET
Status Code:302
Remote Address:127.0.0.1:8888
Response Headers
view source
Cache-Control:no-cache, no-store, max-age=0, must-revalidate
Content-Language:zh-CN
Content-Length:0
Date:Thu, 08 Sep 2016 14:31:33 GMT
Expires:0
Location:https://localhost:8443/users
Pragma:no-cache
Strict-Transport-Security:max-age=31536000 ; includeSubDomains
X-Application-Context:application:dev:8443
X-Content-Type-Options:nosniff
X-Frame-Options:DENY
X-XSS-Protection:1; mode=block
Request Headers
view source
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding:gzip, deflate, sdch, br
Accept-Language:zh-CN,zh;q=0.8
Authorization:Basic YWRtaW46dGVzdA==
Connection:keep-alive
Host:localhost:8443
Upgrade-Insecure-Requests:1
User-Agent:Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36
最关键的就是location:
Location:https://localhost:8443/users
浏览器获取到这个资源定位后就GET访问获取。所以users的请求是这样的:
Request URL:https://localhost:8443/users
Request Method:GET
Status Code:200
Remote Address:127.0.0.1:8888
**Response Headers**
view source
Cache-Control:no-cache, no-store, max-age=0, must-revalidate
Content-Type:application/json;charset=UTF-8
Date:Thu, 08 Sep 2016 14:31:33 GMT
Expires:0
Pragma:no-cache
Strict-Transport-Security:max-age=31536000 ; includeSubDomains
Transfer-Encoding:chunked
X-Application-Context:application:dev:8443
X-Content-Type-Options:nosniff
X-Frame-Options:DENY
X-XSS-Protection:1; mode=block
**Request Headers**
view source
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding:gzip, deflate, sdch, br
Accept-Language:zh-CN,zh;q=0.8
Authorization:Basic YWRtaW46dGVzdA==
Connection:keep-alive
Host:localhost:8443
Upgrade-Insecure-Requests:1
User-Agent:Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36
redirect的另一个作用是原请求的内容将会被舍弃,即如果是post请求,redirect的时候默认是不带参数的。与之相对应的forward的请求是转发,只有一次请求,并且带body转发过去。
Http 303
303 See Other。通常是指所请求的资源在别的地方,并且同302一样,会在header中的location标明资源的位置。在我的一个是使用过程中,我想要创建一个user,当关于这个user的key已经存在的时候,server将返回303,并且告之这个user的获取位置。
Example
Client request:
POST / HTTP/1.1
Host: www.example.com
Server response:
HTTP/1.1 303 See Other
Location: http://example.org/other
实验
我将要发送post请求创建user,如果user已经存在则返回303
Map<String, Double> users = new HashMap<>();
@ResponseBody
@RequestMapping(value = "/users", method = RequestMethod.POST)
public ResponseEntity createUser(String username){
Double luckNum = users.get(username);
if (luckNum ==null){
double random = Math.random();
users.put(username, random);
return new ResponseEntity(random,HttpStatus.OK);
}else{
MultiValueMap<String,String> headers = new HttpHeaders();
headers.add("Location", "/users/"+username);
return new ResponseEntity(luckNum, headers, HttpStatus.SEE_OTHER);
}
}
@ResponseBody
@RequestMapping(value = "/users/{username}", method = RequestMethod.GET)
public ResponseEntity getUser(@PathVariable("username") String username){
ResponseEntity responseEntity = new ResponseEntity("I'm user, My name is "+ username+ " And my luck num is "+users.get(username), HttpStatus.OK);
return responseEntity;
}
发送
查看拦截
可以看到,post的时候返回303,并且在返回的response的header中添加了:
Location: /users/test
所以see other的意思就是去别的地方看看。值得注意的是,如果返回303,但是没有添加location,那么只会查看一条请求303.而在httpclient的默认处理中,这时候会抛出exception:location not found。