在处理方法入参使用@RequestParam可以把请求参数传递给请求方法，@RequestParam包含的属性值：

--- value ：参数名称

--- required ：是否必须，默认为true，表示请求参数中必须包含对应的参数，否则抛出异常。

--- defaultValue：当请求参数缺少或者有请求参数但值为空时，值采用该设置值。

示例：

1）在HelloWord.java中添加testRequestParam方法：

package com.dx.springlearn.handlers;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
@RequestMapping("class_requestmapping")
public class HelloWord {
    private static String SUCCESS = "success";

    @RequestMapping("/testRequestParam")
    public String testRequestParam(@RequestParam(value = "username") String username,
            @RequestParam(value = "address") String address,
            @RequestParam(value = "age", required = false, defaultValue = "0") int age) {
        System.out.println("testRequestParam, username: " + username + ",address: " + address + ",age: " + age);
        return SUCCESS;
    }
}

2）在index.jsp中插入链接html：

<a
        href="class_requestmapping/testRequestParam?username=abc&address=def&age=26">testRequestParam</a>
    <br>

3）测试。

当请求url为：http://localhost:8080/SpringMVC\_01/class\_requestmapping/testRequestParam?username=abc&address=def&age=26

打印信息为：testRequestParam, username: abc,address: def,age: 26

当请求url为：http://localhost:8080/SpringMVC\_01/class\_requestmapping/testRequestParam?username=abc&address=def&age=

抛出异常：

Jan 04, 2018 8:02:53 PM org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver handleTypeMismatch
警告: Failed to bind request element: org.springframework.beans.TypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'int'; nested exception is java.lang.NumberFormatException: For input string: ""

解决方案，把age定义类型修改为Integer

当请求url为：http://localhost:8080/SpringMVC\_01/class\_requestmapping/testRequestParam?username=abc&address=def

打印信息为：testRequestParam, username: abc,address: def,age: 0

当请求url为：http://localhost:8080/SpringMVC\_01/class\_requestmapping/testRequestParam?username=abc

抛出异常：

HTTP Status 400 - Required String parameter 'address' is not present