chapter05_构建Spring Web应用程序_3_接受请求的输入

接受请求的输入在SpringMVC中一共有__3种__方式

(1) 查询参数

(2) 路径参数

(3) 表单参数

处理查询参数

(1) 在url中添加查询参数

示例

  "/spittles?max=238900&count=50"

(2) 处理方式：添加__@RequestParam__注解

示例

  @Controller
  @RequestMapping("/spittles")
  public class SpittleController {

      ...

      private static final String MAX_LONG_AS_STRING = "9223372036854775807";

      @RequestMapping(method = RequestMethod.GET)
      public String spittles(
          @RequestParam(value = "max", defaultValue = MAX_LONG_AS_STRING) long max,
          @RequestParam(value = "count", defaultValue = "20") int count,
          Model model) {

          model.addAttribute("spittleList", spittleRepository.findSpittles(max, count));

          return "spittles";
      }

      ...
  }

@RequestParam的value属性用来指定参数名称(url和value要对应);

@RequestParam的defaultValue属性用来指定默认值，由于查询参数都是String类型的，所以__defaultValue的值一定要是String__

通过路径参数接受输入

(1) 需求:根据id查询历史输入

(2) 如果使用查询参数的方法@RequestParam，则会有如下代码

  @Controller
  @RequestMapping("/spittles")
  public class SpittleController {

      ...

      private static final String MAX_LONG_AS_STRING = "9223372036854775807";

      @RequestMapping(value="/show", method = RequestMethod.GET)
      public String spittle(
          @RequestParam(value = "spittle_id") long spittleId,
          Model model) {

          model.addAttribute("spittle", spittleRepository.findOne(spittleId));

          return "spittles";
      }

      ...
  }

此时url应该为 “/spittles/show?spittle_id=xxx?”，但是这样不好，我们希望的是做到 “/spittles/xxx”

(3) 处理方式：添加__@PathVariable__注解

示例

  @Controller
  @RequestMapping("/spittles")
  public class SpittleController {

      ...

      private static final String MAX_LONG_AS_STRING = "9223372036854775807";

      @RequestMapping(value = "/{spittleId}", method = RequestMethod.GET)
      public String spittle(
          @PathVariable("spittleId") long spittleId,
          Model model) {

          model.addAttribute("spittle", spittleRepository.findOne(spittleId));

          return "spittle";
      }

      ...
  }

@PathVariable中的代表URL中/xxx的xxx部分，在方法上方的@RequestMapping中使用了__占位符{}__

表单输入

(1) 如果请求中包含大量数据，那么就不能使用__查询参数__和__路径参数__了

(2) 当form中没有指定action属性时，代表提交表单的目标是当前页面本身

(3) 在处理post类型的请求时，在请求处理完成后，最好进行一下__重定向__，这样浏览器的刷新就不会重复提交表单了

示例

  @Controller
  @RequestMapping("/spitter")
  public class SpitterController {

      @RequestMapping(value = "/register", method = POST)
      public String processRegistration(
          String username, String password, String firstName, String lastName, String email) {

          ...

          return "redirect:/spitter/" + spitter.getUsername();
     }
  }

(4) 接受form提交参数的两种方式(一)：直接获取同名参数

示例

registerForm.jsp

  <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
  <%@ page session="false" %>
  <html>
    <head>
      <title>Spitter</title>
      <link rel="stylesheet" type="text/css" href="<c:url value="/resources/style.css" />" >
    </head>
    <body>
      <h1>Register</h1>

      <form method="POST">
        First Name: <input type="text" name="firstName" /><br/>
        Last Name: <input type="text" name="lastName" /><br/>
        Email: <input type="email" name="email" /><br/>
        Username: <input type="text" name="username" /><br/>
        Password: <input type="password" name="password" /><br/>
        <input type="submit" value="Register" />
      </form>
    </body>
  </html>

SpitterController.java

  @Controller
  @RequestMapping("/spitter")
  public class SpitterController {

      @RequestMapping(value = "/register", method = POST)
      public String processRegistration(
          String username, String password, String firstName, String lastName, String email) {

          // If parameters check failed, go back to registerForm.jsp
          if (Spitter.checkIfInputParametersHaveErrors(username, password, firstName, lastName, email)) {

              return "registerForm";
          }

          Spitter spitter = new Spitter(username, password, firstName, lastName, email);

          spitterRepository.save(spitter);

          return "redirect:/spitter/" + spitter.getUsername();
     }
  }

其中，username, password, firstName, lastName, email几个参数在jsp文件和Controller文件中是一一对应的。这种方式比较直观，但是写起来繁琐，特别是要进行输入参数检查的时候

(5)接受form提交参数的两种方式(一)：用同名参数填充对象

示例

registerForm.jsp 同上个示例

SpitterController.java

  @Controller
  @RequestMapping("/spitter")
  public class SpitterController {

      @RequestMapping(value = "/register", method = POST)
      public String processRegistration(Spitter spitter) {

          spitterRepository.save(spitter);

          return "redirect:/spitter/" + spitter.getUsername();
      }
  }

Spitter.java

  public class Spitter {

      ...

      public Spitter(String username, String password, String firstName, String lastName, String email) {
          this(null, username, password, firstName, lastName, email);
      }

      public Spitter(Long id, String username, String password, String firstName, String lastName, String email) {
   
          this.id = id;
          this.username = username;
          this.password = password;
          this.firstName = firstName;
          this.lastName = lastName;
          this.email = email;
      }

      ...
  }

直接使用同名的参数填充进Spitter的构造函数中

(6) 校验form

可以不使用Java的校验API自己手动编写代码校验，但是这样比较麻烦；

比较好的方式是在Spitter类中添加Java的校验API,从Spring3.0起添加了对Java校验API的支持

示例 Spitter.java

  import javax.validation.constraints.NotNull;
  import javax.validation.constraints.Size;
  import org.hibernate.validator.constraints.Email;

  public class Spitter {

      private Long id;

      @NotNull
      @Size(min = 5, max = 16)
      private String username;

      @NotNull
      @Size(min = 5, max = 25)
      private String password;

      @NotNull
      @Size(min = 2, max = 30)
      private String firstName;

      @NotNull
      @Size(min = 2, max = 30)
      private String lastName;

      @NotNull
      @Email
      private String email;

      public Spitter() {
      }

      public Spitter(String username, String password, String firstName, String lastName, String email) {
          this(null, username, password, firstName, lastName, email);
      }

      public Spitter(Long id, String username, String password, String firstName, String lastName, String email) {
      
          this.id = id;
          this.username = username;
          this.password = password;
          this.firstName = firstName;
          this.lastName = lastName;
          this.email = email;
      }

      ...
  }

(7) Java API提供的几个常用校验注解

@AssertTrue

@Digits

@Max

@Min

@NotNull

@Size

@Pattern

(8) 在Controller中启用校验功能: @Valid + Errors

示例

SpitterController.java

  @Controller
  @RequestMapping("/spitter")
  public class SpitterController {

      @RequestMapping(value = "/register", method = POST)
      public String processRegistration(@Valid Spitter spitter, Errors errors) {

          // If parameters check failed, go back to registerForm.jsp
          if (errors.hasErrors()) {
              return "registerForm";
          }

          spitterRepository.save(spitter);

          return "redirect:/spitter/" + spitter.getUsername();
      }
  }

在方法的参数上添加 @Valid注解会告知Spring对这个对象进行参数校验，如果校验出现错误的话，可以通过Errors对象访问到

注意方法的参数顺序必须是 @Valid Mytype myType, Errors error不能改变

重定向
```
  return "redirect:/xxx";
```
转发
```
  return "forward:/xxx";
```

chapter05_构建Spring Web应用程序_3_接受请求的输入

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