springMVC 对参数为null或参数不为null的处理

拼搏现实的明天。 2022-06-11 09:09 376阅读 0赞

### **前台传给后台的参数有时是不固定的，有些参数可能有，有些可能没有，比如获取定位的gps，有的用户有开gps，就有gps参数，有些没有，就没有gps参数，因此，我想让这些参数成为可选的，如果没有传入，则可能填充一个默认值。** ###

#### **在springMVC中，有相应的方法处理参数，根据版本的划分，大致可分为3类：** ####

*  **spring4.1+和jdk1.8以上的运行环境使用Optional，将参数可选化**
 *  **spring3.0+的运行环境使用defaultValue设定默认值**
 *  **spring2.5+的运行环境用if判断是否需要给参数注入默认值**

#### **我们以springMVC（版本:4.3.10）自带的hello world例子说明，如下，controller接收前台(index.html)传来的name参数，打印到greeting.html界面上** ####

*  **index.html**

<!DOCTYPE HTML>
 <html>
 <head> 
 <title>Getting Started: Serving Web Content</title> 
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
 </head>
 <body>
 Get your greeting <a href="/greeting_fourpointone">spring4.1以上--没有参数</a>
 Get your greeting <a href="/greeting_fourpointone?name=wen">spring4.1以上--带参数</a>
 Get your greeting <a href="/greeting_threepointzero">spring3.0以上--没有参数</a>
 Get your greeting <a href="/greeting_threepointzero?name=wen">spring3.0以上--带参数</a>
 Get your greeting <a href="/greeting_twopointfive">spring2.5以上--没有参数</a>
 Get your greeting <a href="/greeting_twopointfive?name=wen">spring2.5以上--带参数</a>
 </body>
 </html>

*  **GreetingController .java**

package wen.hello;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestParam;
 
 @Controller
 public class GreetingController { 
 
 //spring4.1+和jdk1.8以上的运行环境
 @RequestMapping("/greeting_fourpointone")
 public String greeting_spring_version_fourpointone(@RequestParam("name") Optional<String> name, Model model) {
 model.addAttribute("name", name);
 return "greeting";
 }
 
 //spring3.0+的运行环境
 @RequestMapping("/greeting_threepointzero")
 public String greeting_spring_version_threepointzero(@RequestParam(value="name", required=false, defaultValue="World") String name, Model model) {
 model.addAttribute("name", name);
 return "greeting";
 }
 
 //spring2.5+的运行环境
 @RequestMapping("/greeting_twopointfive")
 public String greeting_spring_version_twopointfive(@RequestParam(value = "name", required = false) String name, Model model) {
 if (name == null) {
 name = "world";
 }
 model.addAttribute("name", name);
 return "greeting";
 }
 
 }

*  **greeting.html**

<!DOCTYPE HTML>
 <html xmlns:th="http://www.thymeleaf.org">
 <head> 
 <title>Getting Started: Serving Web Content</title> 
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
 </head>
 <body>
 
 </body>
 </html>

*  **运行**

![这里写图片描述][SouthEast]

*  **在浏览器输入：*[http://localhost:8080/][http_localhost_8080]* 测试**  
      
    ![这里写图片描述][SouthEast 1]

[SouthEast]: /images/20220611/6aa5a1f80073416db4dfeba7b9a5f812.png
[http_localhost_8080]: http://localhost:8080/
[SouthEast 1]: /images/20220611/88b489997f7d473082f6a069b5a133d2.png