Pemetaan Permintaan Musim Bunga

Pengaturcaraan

1. Gambaran keseluruhan

Dalam tutorial ini, kita akan memberi tumpuan kepada salah satu anotasi utama di Spring MVC: @RequestMapping.

Secara sederhana, anotasi digunakan untuk memetakan permintaan web ke kaedah Spring Controller.

2. @ Asas Permintaan Pemetaan

Mari kita mulakan dengan contoh mudah: memetakan permintaan HTTP ke kaedah menggunakan beberapa kriteria asas.

2.1. @RequestMapping - mengikut Laluan

@RequestMapping(value = "/ex/foos", method = RequestMethod.GET) @ResponseBody public String getFoosBySimplePath() { return "Get some Foos"; }

Untuk menguji pemetaan ini dengan perintah ikal sederhana , jalankan:

curl -i //localhost:8080/spring-rest/ex/foos

2.2. @RequestMapping - Kaedah HTTP

Parameter kaedah HTTP tidak mempunyai lalai. Jadi, jika kita tidak menentukan nilai, ia akan memetakan ke permintaan HTTP.

Berikut adalah contoh mudah, serupa dengan yang sebelumnya, tetapi kali ini dipetakan untuk permintaan HTTP POST:

@RequestMapping(value = "/ex/foos", method = POST) @ResponseBody public String postFoos() { return "Post some Foos"; }

Untuk menguji POST melalui arahan curl :

curl -i -X POST //localhost:8080/spring-rest/ex/foos

3. Permintaan Pemetaan dan HTTP Header

3.1. @RequestMapping With Atribut tajuk

Pemetaan dapat dipersempit lebih jauh dengan menentukan tajuk untuk permintaan:

@RequestMapping(value = "/ex/foos", headers = "key=val", method = GET) @ResponseBody public String getFoosWithHeader() { return "Get some Foos with Header"; }

Untuk menguji operasi, kami akan menggunakan sokongan header curl :

curl -i -H "key:val" //localhost:8080/spring-rest/ex/foos

malah pelbagai tajuk melalui atribut header @RequestMapping :

@RequestMapping( value = "/ex/foos", headers = { "key1=val1", "key2=val2" }, method = GET) @ResponseBody public String getFoosWithHeaders() { return "Get some Foos with Header"; }

Kita boleh mengujinya dengan arahan:

curl -i -H "key1:val1" -H "key2:val2" //localhost:8080/spring-rest/ex/foos

Perhatikan bahawa untuk sintaks curl , titik dua memisahkan kunci header dan nilai header, sama seperti pada spesifikasi HTTP, sementara pada Spring, tanda sama digunakan.

3.2. @RequestMapping Menggunakan dan Menghasilkan

Pemetaan jenis media yang dihasilkan dengan kaedah pengawal perlu diberi perhatian khusus.

Kami dapat memetakan permintaan berdasarkan header Terima melalui atribut header @RequestMapping yang diperkenalkan di atas:

@RequestMapping( value = "/ex/foos", method = GET, headers = "Accept=application/json") @ResponseBody public String getFoosAsJsonFromBrowser() { return "Get some Foos with Header Old"; }

Pencocokan untuk cara mendefinisikan header Accept ini fleksibel - ia menggunakan mengandungi bukan yang sama, jadi permintaan seperti berikut masih akan dipetakan dengan betul:

curl -H "Accept:application/json,text/html" //localhost:8080/spring-rest/ex/foos

Bermula dengan Spring 3.1, yang @RequestMapping anotasi kini yang menghasilkan dan consumes sifat-sifat , khusus untuk tujuan ini:

@RequestMapping( value = "/ex/foos", method = RequestMethod.GET, produces = "application/json" ) @ResponseBody public String getFoosAsJsonFromREST() { return "Get some Foos with Header New"; }

Juga, pemetaan jenis lama dengan atribut header akan secara automatik ditukar kepada mekanisme penghasilan baru bermula dengan Spring 3.1, sehingga hasilnya akan sama.

Ini dimakan melalui curl dengan cara yang sama:

curl -H "Accept:application/json" //localhost:8080/spring-rest/ex/foos

Selain itu, menghasilkan menyokong pelbagai nilai juga:

@RequestMapping( value = "/ex/foos", method = GET, produces = { "application/json", "application/xml" } )

Perlu diingat bahawa ini - cara lama dan baru untuk menentukan tajuk Terima - pada dasarnya adalah pemetaan yang sama, jadi Spring tidak akan membenarkannya bersama.

Setelah kedua-dua kaedah ini aktif akan menghasilkan:

Caused by: java.lang.IllegalStateException: Ambiguous mapping found. Cannot map 'fooController' bean method java.lang.String org.baeldung.spring.web.controller .FooController.getFoosAsJsonFromREST() to { [/ex/foos], methods=[GET],params=[],headers=[], consumes=[],produces=[application/json],custom=[] }: There is already 'fooController' bean method java.lang.String org.baeldung.spring.web.controller .FooController.getFoosAsJsonFromBrowser() mapped.

Satu nota terakhir pada yang baru menghasilkan dan consumes mekanisme, yang berkelakuan berbeza daripada kebanyakan anotasi lain: Apabila tertentu pada tahap jenis, penjelasan kaedah-peringkat tidak melengkapi tetapi mengatasi maklumat jenis-peringkat.

Dan tentu saja, jika anda ingin menggali lebih mendalam untuk membina REST API dengan Spring, lihat kursus REST dengan Spring yang baru .

4. Permintaan Pemetaan Dengan Pembolehubah Laluan

Sebahagian dari URI pemetaan dapat diikat kepada pemboleh ubah melalui anotasi @PathVariable .

4.1. Single @PathVariable

Contoh mudah dengan pemboleh ubah jalur tunggal:

@RequestMapping(value = "/ex/foos/{id}", method = GET) @ResponseBody public String getFoosBySimplePathWithPathVariable( @PathVariable("id") long id) { return "Get a specific Foo with/ex/foos/{id}", method = GET) @ResponseBody public String getFoosBySimplePathWithPathVariable( @PathVariable String id) { return "Get a specific Foo with2-multiple-pathvariable">4.2. Multiple @PathVariable
A more complex URI may need to map multiple parts of the URI to multiple values:
@RequestMapping(value = "/ex/foos/{fooid}/bar/{barid}", method = GET) @ResponseBody public String getFoosBySimplePathWithPathVariables (@PathVariable long fooid, @PathVariable long barid) { return "Get a specific Bar with from a Foo with3-pathvariable-with-regex">4.3. @PathVariable With Regex
Regular expressions can also be used when mapping the @PathVariable.
For example, we will restrict the mapping to only accept numerical values for the id:
@RequestMapping(value = "/ex/bars/{numericId:[\\d]+}", method = GET) @ResponseBody public String getBarsBySimplePathWithPathVariable( @PathVariable long numericId) { return "Get a specific Bar withrequest-param">5. RequestMapping With Request Parameters
@RequestMapping allows easy mapping of URL parameters with the @RequestParam annotation. 
We are now mapping a request to a URI:
//localhost:8080/spring-rest/ex/bars?id=100
@RequestMapping(value = "/ex/bars", method = GET) @ResponseBody public String getBarBySimplePathWithRequestParam( @RequestParam("id") long id) { return "Get a specific Bar with/ex/bars", params = "id", method = GET) @ResponseBody public String getBarBySimplePathWithExplicitRequestParam( @RequestParam("id") long id) { return "Get a specific Bar with/ex/bars", params = { "id", "second" }, method = GET) @ResponseBody public String getBarBySimplePathWithExplicitRequestParams( @RequestParam("id") long id) { return "Narrow Get a specific Bar withcorner-cases">6. RequestMapping Corner Cases
6.1. @RequestMapping — Multiple Paths Mapped to the Same Controller Method
Although a single @RequestMapping path value is usually used for a single controller method (just good practice, not a hard and fast rule), there are some cases where mapping multiple requests to the same method may be necessary.
In that case, the value attribute of @RequestMapping does accept multiple mappings, not just a single one:
@RequestMapping( value = { "/ex/advanced/bars", "/ex/advanced/foos" }, method = GET) @ResponseBody public String getFoosOrBarsByPath() { return "Advanced - Get some Foos or Bars"; }
Now both of these curl commands should hit the same method:
curl -i //localhost:8080/spring-rest/ex/advanced/foos curl -i //localhost:8080/spring-rest/ex/advanced/bars
6.2. @RequestMapping — Multiple HTTP Request Methods to the Same Controller Method
Multiple requests using different HTTP verbs can be mapped to the same controller method:
@RequestMapping( value = "/ex/foos/multiple", method = { RequestMethod.PUT, RequestMethod.POST } ) @ResponseBody public String putAndPostFoos() { return "Advanced - PUT and POST within single method"; }
With curl, both of these will now hit the same method:
curl -i -X POST //localhost:8080/spring-rest/ex/foos/multiple curl -i -X PUT //localhost:8080/spring-rest/ex/foos/multiple
6.3. @RequestMapping — a Fallback for All Requests
To implement a simple fallback for all requests using a particular HTTP method, for example, for a GET:
@RequestMapping(value = "*", method = RequestMethod.GET) @ResponseBody public String getFallback() { return "Fallback for GET Requests"; }
or even for all requests:
@RequestMapping( value = "*", method = { RequestMethod.GET, RequestMethod.POST ... }) @ResponseBody public String allFallback() { return "Fallback for All Requests"; }
6.4. Ambiguous Mapping Error
The ambiguous mapping error occurs when Spring evaluates two or more request mappings to be the same for different controller methods. A request mapping is the same when it has the same HTTP method, URL, parameters, headers, and media type.
For example, this is an ambiguous mapping:
@GetMapping(value = "foos/duplicate" ) public String duplicate() { return "Duplicate"; } @GetMapping(value = "foos/duplicate" ) public String duplicateEx() { return "Duplicate"; }
The exception thrown usually does have error messages along these lines:
Caused by: java.lang.IllegalStateException: Ambiguous mapping. Cannot map 'fooMappingExamplesController' method public java.lang.String org.baeldung.web.controller.FooMappingExamplesController.duplicateEx() to {[/ex/foos/duplicate],methods=[GET]}: There is already 'fooMappingExamplesController' bean method public java.lang.String org.baeldung.web.controller.FooMappingExamplesController.duplicate() mapped.
A careful reading of the error message points to the fact that Spring is unable to map the method org.baeldung.web.controller.FooMappingExamplesController.duplicateEx(), as it has a conflicting mapping with an already mapped org.baeldung.web.controller.FooMappingExamplesController.duplicate().
The code snippet below will not result in ambiguous mapping error because both methods return different content types:
@GetMapping(value = "foos/duplicate", produces = MediaType.APPLICATION_XML_VALUE) public String duplicateXml() { return "Duplicate"; } @GetMapping(value = "foos/duplicate", produces = MediaType.APPLICATION_JSON_VALUE) public String duplicateJson() { return "{\"message\":\"Duplicate\"}"; }
This differentiation allows our controller to return the correct data representation based on the Accepts header supplied in the request.
Another way to resolve this is to update the URL assigned to either of the two methods involved.
7. New Request Mapping Shortcuts
 Spring Framework 4.3 introduced a few new HTTP mapping annotations, all based on @RequestMapping : 

            
    
             
  • @GetMapping
    • 
             
  • @PostMapping
    • 
             
  • @PutMapping
    • 
             
  • @DeleteMapping
    • 
             
  • @PatchMapping
    • 
            
 These new annotations can improve the readability and reduce the verbosity of the code. 
 Let's look at these new annotations in action by creating a RESTful API that supports CRUD operations: 
@GetMapping("/{id}") public ResponseEntity getBazz(@PathVariable String id){ return new ResponseEntity(new Bazz(id, "Bazz"+id), HttpStatus.OK); } @PostMapping public ResponseEntity newBazz(@RequestParam("name") String name){ return new ResponseEntity(new Bazz("5", name), HttpStatus.OK); } @PutMapping("/{id}") public ResponseEntity updateBazz( @PathVariable String id, @RequestParam("name") String name) { return new ResponseEntity(new Bazz(id, name), HttpStatus.OK); } @DeleteMapping("/{id}") public ResponseEntity deleteBazz(@PathVariable String id){ return new ResponseEntity(new Bazz(id), HttpStatus.OK); }
 A deep dive into these can be found here. 
8. Spring Configuration
The Spring MVC Configuration is simple enough, considering that our FooController is defined in the following package:
package org.baeldung.spring.web.controller; @Controller public class FooController { ... }
We simply need a @Configuration class to enable the full MVC support and configure classpath scanning for the controller:
@Configuration @EnableWebMvc @ComponentScan({ "org.baeldung.spring.web.controller" }) public class MvcConfig { // }
9. Conclusion
This article focused on the @RequestMapping annotation in Spring, discussing a simple use case, the mapping of HTTP headers, binding parts of the URI with @PathVariable, and working with URI parameters and the @RequestParam annotation.
If you'd like to learn how to use another core annotation in Spring MVC, you can explore the @ModelAttribute annotation here.
The full code from the article is available over on GitHub.