How to get request data in SpringMVC?

1. Obtain request parameters

The format of client request parameters is: name=value&name=value... The server needs to obtain the requested parameters, sometimes Data also needs to be encapsulated. SpringMVC can receive the following types of parameters:

1) Basic type parameters:

The parameter name of the business method in the Controller must be consistent with the name of the request parameter. Values ​​are automatically mapped and matched.

//http://localhost:8080/project/quick9?username=zhangsan&age=12
@RequestMapping("/quick9")
@ResponseBody
public void quickMethod9(String username,int age) throws IOException {
    System.out.println(username);
    System.out.println(age);
}

2) POJO type parameters:

The attribute name of the POJO parameter of the business method in the Controller is consistent with the name of the request parameter, and the parameter value will be automatically mapped and matched.

//http://localhost:8080/itheima_springmvc1/quick9?username=zhangsan&age=12
public class User {
    private String username;
    private int age;
    getter/setter…
}
@RequestMapping("/quick10")
@ResponseBody
public void quickMethod10(User user) throws IOException {
    System.out.println(user);
}

3) Array type parameters

The name of the business method array in the Controller is consistent with the name of the request parameter, and the parameter values ​​will be automatically mapped and matched.

//http://localhost:8080/project/quick11?strs=111&strs=222&strs=333
@RequestMapping("/quick11")
@ResponseBody
public void quickMethod11(String[] strs) throws IOException {
    System.out.println(Arrays.asList(strs));
}

4) Collection type parameters

When obtaining collection parameters, you must wrap the collection parameters into a POJO.

<form action="${pageContext.request.contextPath}/quick12" method="post">
 <input type="text" name="userList[0].username"><br>
 <input type="text" name="userList[0].age"><br>
 <input type="text" name="userList[1].username"><br>
 <input type="text" name="userList[1].age"><br>
 <input type="submit" value="提交"><br>
</form>

@RequestMapping("/quick12")
@ResponseBody
public void quickMethod12(Vo vo) throws IOException {
    System.out.println(vo.getUserList());
}

When submitting using ajax, you can specify the contentType as json, then use @RequestBody in the method parameter position to directly receive the collection data without using POJO for packaging.

<script>
//模拟数据
var userList = new Array();
userList.push({username: "zhangsan",age: "20"});
userList.push({username: "lisi",age: "20"});
$.ajax({
type: "POST",
url: "/itheima_springmvc1/quick13",
data: JSON.stringify(userList),
contentType : &#39;application/json;charset=utf-8&#39;
});
</script>

@RequestMapping("/quick13")
@ResponseBody
public void quickMethod13(@RequestBody List<User> userList) throws 
IOException {
    System.out.println(userList);
}

Note: Through the Google developer tool packet capture, it was found that the jquery file was not loaded. The reason is that the url-pattern of the SpringMVC front-end controller DispatcherServlet is configured with /, which means that all resources are filtered. , we can specify the released static resources in the following two ways: • Specify the released resources in the spring-mvc.xml configuration file

<mvc:resources mapping="/js/**" location="/js/"/>

• Or use the tag

2. The problem of garbled request

When a post request is made, the data will be garbled. We can set a filter in web.xml to filter the encoding.

<!--资源过滤器-->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

When the requested parameter name is inconsistent with the Controller's business method parameter name, you need to display the binding through the @RequestParam annotation.

<form action="${pageContext.request.contextPath}/quick14" method="post">
 <input type="text" name="name"><br>
 <input type="submit" value="提交"><br>
</form>

3. Parameter binding annotation @RequestParam

The annotation @RequestParam also has the following parameters that can be used:

value:	Request parameter name
required:	Whether the specified request parameter must be included, the default is true, if there is no such parameter when submitting, an error will be reported
defaultValue:	When no request parameters are specified, the specified default value is used for assignment

@RequestMapping("/quick14")
@ResponseBody
public void quickMethod14(@RequestParam(value="name",required = 
false,defaultValue = "defaultname") String username) throws IOException {
System.out.println(username);
}

4. Get Restful style parameters

Restful is a software architectural style and design style, not a standard. It just provides a set of design principles and constraints. It is mainly used for client-server interactive software. Software designed based on this style can be simpler, more layered, and easier to implement caching mechanisms.

Restful style requests use "url request method" to indicate the purpose of a request. The four verbs in the HTTP protocol indicating the operation method are as follows:

##DELETE:Delete the resource##PUT:POST:##For example:

GET:	Get the resource
Update resources
New resource

/user/1 GET: Get the user with id = 1/user/1 DELETE: Delete user/user/1 with id = 1 PUT:Update useruser with id = 1 POST ：Add new user1 in the above url address/user/1 is the request parameter to be obtained, and placeholders can be used in SpringMVC Perform parameter binding. The address /user/1 can be written as /user/{id}, and the placeholder {id} corresponds to the value of 1. In the business method, we can use the @PathVariable annotation to obtain placeholder matching.

//http://localhost:8080/itheima_springmvc1/quick19/zhangsan
@RequestMapping("/quick19/{name}")
@ResponseBody
public void quickMethod19(@PathVariable(value = "name",required = true) String name){
System.out.println(name);
}

5. Custom type converter

Although SpringMVC has provided some commonly used type converters by default, such as converting a string submitted by the client into an int type Make parameter settings.

• But not all data types provide converters. If they are not provided, you need to customize the converter. For example, date type data requires a custom converter.

• Development steps for custom type converters:

① Define the converter class to implement the Converter interface

public class DateConverter implements Converter<String, Date> {
    @Override
    public Date convert(String source) {
        SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd");
        Date date = null;
        try {
            date = format.parse(source);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return date;
    }
}

② Configure in spring-mvc.xml Declare the converter

<!--配置自定义转换器-->
    <bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
        <property name="converters">
            <list>
                <bean class="converter.DateConverter"/>
            </list>
        </property>
    </bean>

in the file ③ Reference the converter

 <!--注解驱动-->
    <mvc:annotation-driven conversion-service="conversionService"/>

in 6. Obtain the request header

@RequestHeader

Use @RequestHeader to obtain the request header information, which is equivalent to request.getHeader(name) learned in the web stage. The attributes annotated by @RequestHeader are as follows:

value The name of the request headerrequiredWhether this request header must be carried

@RequestMapping("/quick17")
@ResponseBody
public void quickMethod17(@RequestHeader(value = "User-Agent",required = false) String 
headerValue){
    System.out.println(headerValue);
}

@CookieValue

使用@CookieValue可以获得指定Cookie的值 @CookieValue注解的属性如下：

value	指定cookie的名称
required	是否必须携带此cookie

@RequestMapping("/quick18")
@ResponseBody
public void quickMethod18(@CookieValue(value = "JSESSIONID",required = false) String jsessionid){
    System.out.println(jsessionid);
}

7.文件上传

文件上传客户端三要素：

• 表单项type=“file”

• 表单的提交方式是post

• 表单的enctype属性是多部分表单形式，及enctype=“multipart/form-data”

<form action="${pageContext.request.contextPath}/quick20" method="post" 
enctype="multipart/form-data">
名称：<input type="text" name="name"><br>
文件：<input type="file" name="file"><br>
 <input type="submit" value="提交"><br>
</form>

文件上传步骤

① 在pom.xml导入fileupload和io坐标

<!--文件下载-->
    <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.4</version>
    </dependency>
    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.6</version>
    </dependency>

② 配置文件上传解析器

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="defaultEncoding" value="UTF-8"/>
        <property name="maxUploadSize" value="500000"/>
    </bean>

③ 编写文件上传代码

@RequestMapping("/quick8")
    @ResponseBody
    public void save8(String name, MultipartFile uploadfile) {
        System.out.println("save8 running...");
        System.out.println(name);
        String filename = uploadfile.getOriginalFilename();
        try {
            uploadfile.transferTo(new File("D:\\upload\\"+filename));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

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