@ModelAttribute详解

迈不过友情╰ 2022-05-25 14:27 254阅读 0赞

**@ModelAttribute简介**

@ModelAttribute是Spring MVC最重要的注释之一。

1、此注释可作为方法参数或方法声明之前使用。

2、此注释的主要目的是将请求参数或表单字段绑定到模型对象。模型对象可以使用请求参数(如示例中所示)或已经存储在会话对象中来生成。

3、注意，这个@ModelAttribute方法是在调用@RequestMapping的控制器方法之前调用的。序列背后的逻辑是，在控制器方法内部开始任何处理之前，必须创建模型对象

下面是@ModelAttribute的源码，可以看得更直观一些

/**
     * Annotation that binds a method parameter or method return value * to a named model attribute, exposed to a web view. Supported
     * for controller classes with {@link RequestMapping @RequestMapping}
     * methods.    #简要理解就是可以作为方法参数和方法声明之前使用
     *
     * <p>Can be used to expose command objects to a web view, using
     * specific attribute names, through annotating corresponding
     * parameters of an {@link RequestMapping @RequestMapping} method.
     *
     * <p>Can also be used to expose reference data to a web view
     * through annotating accessor methods in a controller class with
     * {@link RequestMapping @RequestMapping} methods. Such accessor
     * methods are allowed to have any arguments that
     * {@link RequestMapping @RequestMapping} methods support, returning
     * the model attribute value to expose.
     *
     * <p>Note however that reference data and all other model content is
     * not available to web views when request processing results in an
     * {@code Exception} since the exception could be raised at any time
     * making the content of the model unreliable. For this reason
     * {@link ExceptionHandler @ExceptionHandler} methods do not provide
     * access to a {@link Model} argument.
     *
     * @author Juergen Hoeller
     * @author Rossen Stoyanchev
     * @since 2.5
     */
    @Target({ElementType.PARAMETER, ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface ModelAttribute {
    
    	/**
    	 * Alias for {@link #name}.
    	 */
    	@AliasFor("name")
    	String value() default "";
                .
                .后面还有，这是截取了一部分

Example

**ModelAttributeExampleController.java**

package javabeat.net;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.ModelAttribute;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RequestParam;
    
    @Controller
    public class ModelAttributeExampleController {
    	@Autowired
    	private UserDetails userDetails;
    	@RequestMapping(value="/modelexample")
    	public String getMethod(@ModelAttribute UserDetails userDetails){
    		System.out.println("User Name : " + userDetails.getUserName());
    		System.out.println("Email Id : " + userDetails.getEmailId());
    		return "example";
    	}
    
    	//This method is invoked before the above method
    	@ModelAttribute
    	public UserDetails getAccount(@RequestParam String user, @RequestParam String emailId){
    		System.out.println("User Value from Request Parameter : " + user);
    		userDetails.setUserName(user);
    		userDetails.setEmailId(emailId);
    		return userDetails;
    	}
    }

**UserDetails.java**

package javabeat.net;
    
    public class UserDetails {
    	private String userName;
    	private String emailId;
    	public String getUserName() {
    		return userName;
    	}
    	public void setUserName(String userName) {
    		this.userName = userName;
    	}
    	public String getEmailId() {
    		return emailId;
    	}
    	public void setEmailId(String emailId) {
    		this.emailId = emailId;
    	}
    }

参考资料：

[相关资料参考1][1]

[相关资料参考2][2]

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[1]: http://www.baeldung.com/spring-mvc-and-the-modelattribute-annotation
[2]: https://javabeat.net/modelattribute-spring-mvc/
[PathVariable _ URI Template Patterns in Spring MVC]: https://javabeat.net/pathvariable-template-patterns-spring-mvc/
[RequestHeader in Spring MVC]: https://javabeat.net/requestheader-spring-mvc/
[Spring MVC Annotations]: https://javabeat.net/spring-mvc-annotations/
[How to get current username in Spring Security_]: https://javabeat.net/logged-username-spring-security/
[Exception Handling With _ControllerAdvice in Spring 3.2]: https://javabeat.net/exception-controlleradvice-spring-3-2/