使用Spring MVC編寫RESTful Controller

時間 2019-11-10

標籤使用 spring mvc 編寫 restful controller 欄目 Spring 简体版

原文原文鏈接

一、Spring對REST的支持html

Spring3（這裏討論Spring3.2+）對Spring MVC的一些加強功能爲REST提供了良好的支持。Spring對開發REST資源提供如下支持：web

操做方式：控制器能夠處理全部的HTTP方法，包含4個主要的REST方法：GET、PUT、DELETE以及POST。Spring的表單綁定JSP標籤庫的<form:form>標籤以及新的HiddenHttpMethodFilter，使得經過HTML表單提交的PUT和DELETE請求成爲可能
資源標識：新的@PathVariable註解使得控制器可以處理參數化的URL
資源表述方法1：經過使用Spring的視圖解析器，資源能夠以各類形式進行表述，包括XML、JSON、Atom和RSS（）。使用新的ContentNegotiatingViewResolver來選擇最合適客戶端的表述
資源表述方法2：經過使用@ResponseBody註解和各類HttpMethodConverter實現來達到。@RequestBody註解記憶HttpMethodConverter實現能夠將傳入的HTTP數據轉化爲傳入控制器方法的Java對象
REST客戶端：RestTemplate簡化了客戶端對REST資源的使用

二、參數化URLspring

Spring3.0中引入了新的@PathVariable註解，幫助Controller使用面向資源的方式處理請求。如：json

 1 @Controller
 2 @RequestMapping(value="/spitters")
 3 public class SpittleController{
 4     private SpitterService spitterService;
 5     ...
 6     @RequestMapping(value="/{id}", method= RequestMethod.PUT)
 7     @ResponseStatus(HttpStatus.NO_CONTENT)
 8     public void putSpittle(@PathVariable("id")) long id,
 9                            @Valid Spittle spittle)
10     {
11         spitterService.saveSpittle(spittle);
12     }
13 }

三、協商資源表述c#

「協商資源表述」即肯定一個HTTP請求所須要返回的資源格式，HTML、XML仍是JSON等。按優先級，Spring MVC依次經過如下三個條件肯定客戶端須要什麼類型的內容表述：spring-mvc

URL路徑上添加擴展名，如 http://myserver/myapp/accounts/list.html 或者 http://myserver/myapp/accounts/list.xls。
URL參數，如 http://myserver/myapp/accounts/list?format=xls，參數名默認爲「format」，但也能夠更改。
經過HTTP請求的Accept頭部信息肯定返回資源格式，但因爲客戶端的處理不一樣，這個方法並不太可靠。

JAF（JavaBeans Activation Framework）可提供由擴展名（或URL參數）到資源格式的自動映射機制（如json->"application/json"），這時classpath下必須有activation.jar包。mvc

Spring MVC經過ContentNegotiationManager來進行資源協商，通常配置以下：app

 1 <bean id="contentNegotiationManager"
 2       class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
 3 <property name="favorPathExtension" value="false" />
 4 <property name="favorParameter" value="true" />
 5 <property name="parameterName" value="mediaType" />
 6 <property name="ignoreAcceptHeader" value="true"/>
 7 <property name="useJaf" value="false"/>
 8 <property name="defaultContentType" value="application/json" />
 9 
10 <property name="mediaTypes">
11     <map>
12         <entry key="json" value="application/json" />
13         <entry key="xml" value="application/xml" />
14     </map>
15 </property>
16 </bean>

以上配置表示：不使用路徑擴展名方式，也不使用Accept頭信息方式，僅使用URL參數方式肯定資源類型，URL參數名使用「mediaType」代替默認的「format」，不使用JAF而是自行定義URL參數到資源格式的映射，這裏只定義了JSON和XML。jsp

四、表述資源（一）ide

Spring MVC經過兩種方式將Java表述形式的資源轉化爲發送給客戶端的表述形式：

基於視圖渲染進行協商（@ContentNegotiatingViewResolver）
HTTP消息轉換器（HttpMessageConverters）

首先是第一種方式，使用HttpMessageConverters表述資源。當ContentNegotiationManager配置以下，且類路徑下包含JAXB和Jackson包時，Spring MVC將自動匹配使用哪一種HttpMessageCoverter。

ContentNegotiationManager配置：

 1 <!-- enable the "produces" annotation of "RequestMapping" -->
 2 <mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" />
 3 
 4 <!-- Simple strategy: only path extension is taken into account -->
 5 <bean id="cnManager"
 6       class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
 7 <property name="favorPathExtension" value="true"/>
 8 <property name="ignoreAcceptHeader" value="true" />
 9 <property name="defaultContentType" value="text/html" />
10 <property name="useJaf" value="false"/>
11 
12 <property name="mediaTypes">
13     <map>
14         <entry key="html" value="text/html" />
15         <entry key="json" value="application/json" />
16         <entry key="xml" value="application/xml" />
17     </map>
18 </property>
19 </bean>

Controller:

 1 @Controller
 2 class AccountController {
 3     // RESTful method, use MappingJacksonHttpMessageConverter and Jaxb2RootElementHttpMessageConverter automatically
 4     //accounts.json -> application/json
 5     //accounts.xml -> text/xml
 6     @RequestMapping(value="/accounts", produces={"application/xml", "application/json"})
 7     @ResponseStatus(HttpStatus.OK)
 8     public @ResponseBody List<Account> listWithMarshalling(Principal principal) {
 9         return accountManager.getAccounts(principal);
10     }
11 
12     // View-based method
13     //accounts.html -> text/html
14     //accounts.others -> text/html
15     @RequestMapping("/accounts")
16     public String listWithView(Model model, Principal principal) {
17         // Call RESTful method to avoid repeating account lookup logic
18         model.addAttribute( listWithMarshalling(principal) );
19 
20         // Return the view to use for rendering the response
21         return ¨accounts/list¨;
22     }
23 }

使用 JAXB 和 Jackson時，須要在account類上添加annotation：

 1 /**
 2  * Represents an account for a member of a financial institution. An account has
 3  * zero or more {@link Transaction}s and belongs to a {@link Customer}. An aggregate entity.
 4  */
 5 @Entity
 6 @Table(name = "T_ACCOUNT")
 7 @XmlRootElement
 8 public class Account {
 9 
10     // data-members omitted ...
11 
12     public Account(Customer owner, String number, String type) {
13         this.owner = owner;
14         this.number = number;
15         this.type = type;
16     }
17 
18     /**
19      * Returns the number used to uniquely identify this account.
20      */
21     @XmlAttribute
22     public String getNumber() {
23         return number;
24     }
25 
26     /**
27      * Get the account type.
28      *
29      * @return One of "CREDIT", "SAVINGS", "CHECK".
30      */
31     @XmlAttribute
32     public String getType() {
33         return type;
34     }
35 
36     /**
37      * Get the credit-card, if any, associated with this account.
38      *
39      * @return The credit-card number or null if there isn't one.
40      */
41     @XmlAttribute
42     public String getCreditCardNumber() {
43         return StringUtils.hasText(creditCardNumber) ? creditCardNumber : null;
44     }
45 
46     /**
47      * Get the balance of this account in local currency.
48      *
49      * @return Current account balance.
50      */
51     @XmlAttribute
52     public MonetaryAmount getBalance() {
53         return balance;
54     }
55 
56 
57     /**
58      * Returns a single account transaction. Callers should not attempt to hold
59      * on or modify the returned object. This method should only be used
60      * transitively; for example, called to facilitate reporting or testing.
61      *
62      * @param name
63      *            the name of the transaction account e.g "Fred Smith"
64      * @return the beneficiary object
65      */
66     @XmlElement   // Make these a nested <transactions> element
67     public Set<Transaction> getTransactions() {
68         return transactions;
69     }
70 
71     // Setters and other methods ...
72 
73 }

View Code

五、表述資源（二）

第二種方式，使用視圖渲染器（View Resolution）。使用ContentNegotiatingViewResolver和ContentNegotiationManager進行配置：

 1 <!-- View resolver that delegates to other view resolvers based on the content type -->
 2 <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
 3 <!-- All configuration is now done by the manager - since Spring V3.2 -->
 4     <property name="contentNegotiationManager" ref="cnManager"/>
 5 </bean>
 6 
 7 <!-- Setup a simple strategy -->
 8 <bean id="cnManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
 9     <property name="ignoreAcceptHeader" value="true"/>
10     <property name="defaultContentType" value="text/html" />
11 </bean>

使用以上配置Spring將根據約定自動查找ViewResolvers，並渲染資源。也可顯式配置ViewResolvers：

 1 <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
 2 <property name="contentNegotiationManager" ref="cnManager"/>
 3 
 4 <!-- Define the view resolvers explicitly -->
 5 <property name="viewResolvers">
 6     <list>
 7         <bean class="org.springframework.web.servlet.view.XmlViewResolver">
 8             <property name="location" value="spreadsheet-views.xml"/>
 9         </bean>
10 
11         <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
12             <property name="prefix" value="WEB-INF/views"/>
13             <property name="suffix" value=".jsp"/>
14         </bean>
15     </list>
16 </property>
17 </bean>