REST架构风格

REST的几条关键原则列举如下：

1.为所有“事物”定义ID

对事物使用一致的命名规则（naming scheme）最主要的好处就是你不需要提出自己的规则——而是依靠某个已被定义，在全球范围中几乎完美运行，并且能被绝大多数人所理解的规则。如果在一个类似于Amazon.com的在线商城中，没有用唯一的ID（一个URI）标识它的每一件商品，可想而知这将是多么可怕的业务决策。 下面是一些你可能想到的URI的例子：

http://example.com/customers/1234
http://example.com/orders/2007/10/776654
http://example.com/orders/2007/11

2.将所有事物链接在一起
任何可能的情况下，使用链接指引可以被标识的事物（资源）。也正是超链接造就了现在的Web。
3.使用标准方法
GET、POST、DELETE、PUT
4.资源多重表述
针对不同的需求提供资源多重表述，客户端可以请求返回指定格式的资源如xml
上面的内容来源于http://www.infoq.com/cn/articles/rest-introduction
英文地址http://www.infoq.com/articles/rest-introduction

还有一篇文章Build RESTful web services using Spring 3介绍了如何利用spring 3构建REST风格应用。

下面借用下上篇文章的例子介绍下如何在Spring3下搭建REST应用，首先在web.xml
配置contextConfigLocation

<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
    /WEB-INF/rest-context.xml
</param-value>
</context-param>

<!-- This listener will load other application context file in addition to
            rest-servlet.xml -->
<listener>
<listener-class>
    org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>

<servlet>
<servlet-name>rest</servlet-name>
<servlet-class>
    org.springframework.web.servlet.DispatcherServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>rest</servlet-name>
<url-pattern>/service/*</url-pattern>
</servlet-mapping>

下面是在rest-servlet.xml中配置Spring MVC

<context:component-scan base-package="dw.spring3.rest.controller" />
<!--To enable @RequestMapping process on type level and method level-->
<bean class="org.springframework.web.servlet.mvc.annotation
        .DefaultAnnotationHandlerMapping" />
<bean class="org.springframework.web.servlet.mvc.annotation
        .AnnotationMethodHandlerAdapter" />
<!--Use JAXB OXM marshaller to marshall/unmarshall following class-->
<bean id="jaxbMarshaller"
class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
<property name="classesToBeBound">
    <list>
        <value>dw.spring3.rest.bean.Employee</value>
        <value>dw.spring3.rest.bean.EmployeeList</value>
    </list>
</property>
</bean>
<bean id="employees" class=
    "org.springframework.web.servlet.view.xml.MarshallingView">
<constructor-arg ref="jaxbMarshaller" />
</bean>
<bean id="viewResolver" class=
"org.springframework.web.servlet.view.BeanNameViewResolver" />

  

Listing 3. EmployeeController控制器类

 

@Controller
public class EmployeeController {
@RequestMapping(method=RequestMethod.GET, value="/employee/{id}")
public ModelAndView getEmployee(@PathVariable String id) {
    Employee e = employeeDS.get(Long.parseLong(id));
    return new ModelAndView(XML_VIEW_NAME, "object", e);
}
}

 

Listing 4. EmployeeController in dw.spring3.rest.controller

@RequestMapping(method=RequestMethod.POST, value="/employee")
public ModelAndView addEmployee(@RequestBody String body) {
    Source source = new StreamSource(new StringReader(body));
    Employee e = (Employee) jaxb2Mashaller.unmarshal(source);
    employeeDS.add(e);
    return new ModelAndView(XML_VIEW_NAME, "object", e);
}
@RequestMapping(method=RequestMethod.PUT, value="/employee/{id}")
public ModelAndView updateEmployee(@RequestBody String body) {
    Source source = new StreamSource(new StringReader(body));
    Employee e = (Employee) jaxb2Mashaller.unmarshal(source);
    employeeDS.update(e);
    return new ModelAndView(XML_VIEW_NAME, "object", e);
}
@RequestMapping(method=RequestMethod.DELETE, value="/employee/{id}")
public ModelAndView removeEmployee(@PathVariable String id) {
    employeeDS.remove(Long.parseLong(id));
    List<Employee> employees = employeeDS.getAll();
    EmployeeList list = new EmployeeList(employees);
    return new ModelAndView(XML_VIEW_NAME, "employees", list);
}

Listing 5. getAllEmployees in EmployeeController

 

@RequestMapping(method=RequestMethod.GET, value="/employees")
public ModelAndView getEmployees() {
    List<Employee> employees = employeeDS.getAll();
    EmployeeList list = new EmployeeList(employees);
    return new ModelAndView(XML_VIEW_NAME, "employees", list);
}

Listing 6. EmployeeList class in dw.spring3.rest.bean

 

@XmlRootElement(name="employees")
public class EmployeeList {
    private int count;
    private List<Employee> employees;
    public EmployeeList() {}

    public EmployeeList(List<Employee> employees) {
        this.employees = employees;
        this.count = employees.size();
    }
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }

    @XmlElement(name="employee")
    public List<Employee> getEmployees() {
        return employees;
    }
    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }

}

Listing 7. Define content negotiation

 

<bean class="org.springframework.web.servlet.view
        .ContentNegotiatingViewResolver">
<property name="mediaTypes">
    <map>
    <entry key="xml" value="application/xml"/>
    <entry key="html" value="text/html"/>
    </map>
</property>
<property name="viewResolvers">
    <list>
    <bean class="org.springframework.web.servlet.view
            .BeanNameViewResolver"/>
    <bean class="org.springframework.web.servlet.view
            .UrlBasedViewResolver">
        <property name="viewClass" value=
        "org.springframework.web.servlet.view.JstlView"/>
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    </list>
</property>
</bean>

Listing 8. employees.jsp in /WEB-INF/jsp

<table border=1>
    <thead><tr>
        <th>ID</th>
        <th>Name</th>
        <th>Email</th>
    </tr></thead>
    <c:forEach var="employee" items="${employees.employees}">
    <tr>
        <td>${employee.id}</td>
        <td>${employee.name}</td>
        <td>${employee.email}</td>
    </tr>
    </c:forEach>
</table>

下面演示Clients如何与 REST services交互

 

curl –HAccept:application/xml http://localhost:8080/rest/service/employees

下面返回的xml包含employees

Figure 2. 用浏览器打开的HTML展示

 

下面演示创建一个新的employee到服务端,

curl -X POST -HContent-type:application/xml --data
"<employee><id>3</id><name>guest</name><email>guest@ibm.com</employee>"
http://localhost:8080/rest/service/employee

这样一个新的employee注册好了. 可以用第一个例子的 employee 列表验证下.

PUT 和POST方法类似.

curl -X PUT -HContent-type:application/xml --data
"<employee><id>3</id><name>guest3</name><email>guest3@ibm.com</employee>"
http://localhost:8080/rest/service/employee/3

上面代码更新了编号为3的 employee 数据。

现在spring3的mvc层以及完全支持REST了，你可以很轻松的用Spring APIs和注解去构建RESTful web services.