Spring-MVC注解全解析，忘掉Servlet API

相信大家对spring-mvc（下面直接使用mvc代替）不陌生了。本文为大家详尽讲述mvc为大家提供的各种注解，方便开发，除了某些特定场景，基本可以完全和servlet api解耦，其中很多地方可能困扰大家很久。本文使用的mvc为spring-mvc-3.2，使用maven构建，如果没有用过maven的同学，可以先去看看maven的使用，附上demo源码地址：

https://github.com/a953924393/spring-mvc-annotation.git

RequestMapping

用于类和方法上，只是作用于不同，参数的意义相同，

1. value[]：请求路径名，可以匹配多个
2. method[]：接受的Request的类型，参考org.springframework.web.bind.annotation.RequestMethod
3. params[]：用于窄化请求，即请求中必须匹配param中含有的参数才能映射成功
4. headers[]：同样用于匹配必须请求头中必须包含headers中特定的请求头信息的请求
5. consumes[]：mvc的controller是作为http请求的消费者，请求方是生产者，同样用于限定请求，如consumes = "application/json"
6. produces[]：生产即返回的类型如：produces = "text/plain"

<span style="font-size:14px;">@Controller
@RequestMapping(
        value = {"request"},
        method = {RequestMethod.GET, RequestMethod.POST},
        params = {"create","!add"},
        consumes = {"application/*"},
        produces = {"text/*"}
)
public class RequestMappingController {
    @RequestMapping("mapping")
    public void mapping(String create) {
        System.out.println(create);
    }
}</span>

在上面的demo中，可以使用http://localhost:8080/request/mapping?create=aaa请求，可以接受post和get请求，请求参数中必须含有create，不能含有add参数，只能消费application/*类型的请求，如头信息中包含

<span style="font-size:14px;">Accept:text/html,<strong>application/xhtml+xml,application/xml</strong>;q=0.9,image/webp,*/*;q=0.8</span>

RequestParm

用来处理简单类型的绑定，处理Content-Type: 为 application/x-www-form-urlencoded编码的内容，提交方式GET、POST；处理复杂对象

1. value，参数名
   
2. required，该参数是否必须
   
3. defaultValue，设置他的默认值

@RequestMapping("requestParam")
public void requestParam(@RequestParam(value = "name", required = true, defaultValue = "hello") String name) {
        System.out.println(name);
}

RequestBody

用来处理复杂json对象，常用来处理Content-Type: 不是application/x-www-form-urlencoded编码的内容，例如application/json, application/xml等；

1. required，该参数是否必须

前台请求代码

    var submitRequestBody = function () {
        $.ajax({
            type: "POST",
            url: "hello/requestBody",
            contentType: "application/json",
            //注意，这里必须是string类型，下面注释中的提交方式不能被RequestBody正确映射，注意单引号 <span style="font-family: Arial, Helvetica, sans-serif;">            //data: {"id":1,"name":"cxh","password":"cxh123","boo<span style="white-space:pre">			</span>//kList":[{"id":123,"name":"java core"}]},
<span style="white-space:pre">		</span>        data: '{"id":1,"name":"cxh","password":"cxh123","bookList":[{"id":123,"name":"java core"}]}', success: function (data) { alert(data); } }) }</span>

一般会遇到以下错误：

HTTP Status 415 -

type Status report

message

description The server refused this request because the request entity is in a format not supported by the requested resource for the requested method.

这种错误一般发生于

1. 没有json的解析包，所需包，请看源码，或者查看日志打印的信息，添加所需的jar
2. 没有设置content-Type:"application/json"
3. json不够标准，会发生400错误，spring所使用的json解析包需要非常标准的json，如：{name:"jack"}是不标准的，必须是{"name":"jack"}，

后台代码：

    @RequestMapping(value = "requestBody", consumes = "application/json")
    @ResponseBody
    public User requestBody(@RequestBody User user) {
        System.out.println(user);
        return user;
    }

User对象

public class User {
    private Integer  id;
    private String name;
    private String password;
    private List<Book> bookList;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public List<Book> getBookList() {
        return bookList;
    }

    public void setBookList(List<Book> bookList) {
        this.bookList = bookList;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                ", bookList=" + bookList +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        User user = (User) o;

        if (bookList != null ? !bookList.equals(user.bookList) : user.bookList != null) return false;
        if (id != null ? !id.equals(user.id) : user.id != null) return false;
        if (name != null ? !name.equals(user.name) : user.name != null) return false;
        if (password != null ? !password.equals(user.password) : user.password != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = id != null ? id.hashCode() : 0;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        result = 31 * result + (password != null ? password.hashCode() : 0);
        result = 31 * result + (bookList != null ? bookList.hashCode() : 0);
        return result;
    }
}

Book对象

public class Book {

    private Integer id;
    private String name;
    private Date  publication;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getPublication() {
        return publication;
    }

    public void setPublication(Date publication) {
        this.publication = publication;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", publication=" + publication +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Book book = (Book) o;

        if (id != null ? !id.equals(book.id) : book.id != null) return false;
        if (name != null ? !name.equals(book.name) : book.name != null) return false;
        if (publication != null ? !publication.equals(book.publication) : book.publication != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = id != null ? id.hashCode() : 0;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        result = 31 * result + (publication != null ? publication.hashCode() : 0);
        return result;
    }
}

PathVariable

这个注解用于参数上，让你很容易构建restful的url

1. value，参数名

前台请求http://localhost:8080/hello/pathVariable/123/chen

后台代码

    @RequestMapping(value = "pathVariable/{id}/{name}")
    public String pathVariable(@PathVariable Integer id, @PathVariable String name) {
        System.out.println(id + name);
        return "hello";
    }

ResponseBody

用在方法上，用于返回一个json类型的字符串

前台请求

Request Headersview 
GET /hello/responseBody HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: zh-CN,zh;q=0.8
Cookie: JSESSIONID=C09D6923C357C127CA408BF68B7FF8A9
Response Headersview  
Content-Type:application/json;charset=UTF-8
Date:Sun, 07 Dec 2014 08:56:15 GMT
Server:Apache-Coyote/1.1
Transfer-Encoding:chunked

后台代码返回一个user对象

    @RequestMapping("responseBody")
    @ResponseBody
    public User responseBody() {
        User user = new User();
        Book book = new Book();
        book.setName("java core");
        book.setId(1);
        book.setPublication(new Date());
        ArrayList<Book> books = new ArrayList<Book>();
        books.add(book);
        user.setId(1);
        user.setName("jack");
        user.setPassword("123asd");
        user.setBookList(books);
        return user;
    }

CookieValue

用于参数上，按照名称获取一个cookie值，源码中采用foreach循环得到cookie，

CookieValue的参数列表

1. value，参数名
   
2. required，该参数是否必须
   
3. defaultValue，设置他的默认值

后台代码

    @RequestMapping("cookieValue")
    public String cookieValue(@CookieValue("JSESSIONID") String jsessionId) {
        System.out.println(jsessionId);
        return "hello";
    }

RequestHeader

获取http头信息中的内容，参数同CookieValue，value的大小写不明感，比如Accept和accept都可以得到accept的值

后台代码

    @RequestMapping("requestHeader")
    public String requestHeader(@RequestHeader String accept) {
        System.out.println(accept);
        return "hello";
    }