Spring中ResponseBodyAdvice的使用详解

responsebodyadvice可以在注解@responsebody将返回值处理成相应格式之前操作返回值。实现这个接口即可完成相应操作。可用于对response 数据的一些统一封装或者加密等操作

1 responsebodyadvice的简介

responsebodyadvice接口和之前记录的requestbodyadvice接口类似, requestbodyadvice是请求到controller之前拦截,做相应的处理操作, 而responsebodyadvice是对controller返回的{@code @responsebody}or a {@code responseentity} 后,{@code httpmessageconverter} 类型转换之前拦截, 进行相应的处理操作后,再将结果返回给客户端.

responsebodyadvice的源代码:

/**   数据的处理顺序向下
 * allows customizing the response after the execution of an {@code @responsebody}
 * or a {@code responseentity} controller method but before the body is written
 * with an {@code httpmessageconverter}.
 *
 * <p>implementations may be registered directly with
 * {@code requestmappinghandleradapter} and {@code exceptionhandlerexceptionresolver}
 * or more likely annotated with {@code @controlleradvice} in which case they
 * will be auto-detected by both.
 *
 * @author rossen stoyanchev
 * @since 4.1
 * @param <t> the body type
 */
public interface responsebodyadvice<t> {

	/**
	 * whether this component supports the given controller method return type
	 * and the selected {@code httpmessageconverter} type.
	 * @param returntype the return type   方法返回的类型
	 * @param convertertype the selected converter type   参数类型装换
	 * @return {@code true} if {@link #beforebodywrite} should be invoked;
	 * {@code false} otherwise
	 * 返回 true 则下面 beforebodywrite方法被调用, 否则就不调用下述方法
	 */
	boolean supports(methodparameter returntype, class<? extends httpmessageconverter<?>> convertertype);

	/**
	 * invoked after an {@code httpmessageconverter} is selected and just before
	 * its write method is invoked.
	 * @param body the body to be written
	 * @param returntype the return type of the controller method
	 * @param selectedcontenttype the content type selected through content negotiation
	 * @param selectedconvertertype the converter type selected to write to the response
	 * @param request the current request
	 * @param response the current response
	 * @return the body that was passed in or a modified (possibly new) instance
	 */
	@nullable
	t beforebodywrite(@nullable t body, methodparameter returntype, mediatype selectedcontenttype,
			class<? extends httpmessageconverter<?>> selectedconvertertype,
			serverhttprequest request, serverhttpresponse response);

}

说明:

• supports方法: 判断是否要执行beforebodywrite方法,true为执行,false不执行. 通过该方法可以选择哪些类或那些方法的response要进行处理, 其他的不进行处理.
• beforebodywrite方法: 对response方法进行具体操作处理

{@code @responsebody} 返回响应体, 例如list集合

{@code responseentity} 返回响应实体对象,例如user对象

2 responsebodyadvice的使用

1 准备一个springboot项目环境

2 添加一个响应拦截类

@controlleradvice
public class baseresponsebodyadvice implements responsebodyadvice<object> {


    @override
    public boolean supports(methodparameter returntype, class convertertype) {
        return true;
    }

    @override
    public object beforebodywrite(object body, methodparameter returntype,
            mediatype selectedcontenttype, class selectedconvertertype, serverhttprequest request,
            serverhttpresponse response) {

        // 遇到feign接口之类的请求, 不应该再次包装,应该直接返回
        // 上述问题的解决方案: 可以在feign拦截器中,给feign请求头中添加一个标识字段, 表示是feign请求
        // 在此处拦截到feign标识字段, 则直接放行 返回body.

        system.out.println("响应拦截成功");

        if (body instanceof baseresponse) {
            return body;
        } else if (body == null) {
            return baseresponse.ok();
        } else {
            return baseresponse.ok(body);
        }
    }
}

3 添加一个返回包装类

@data
@allargsconstructor
@noargsconstructor
public class baseresponse<t> {

    private t data;
    private int status = 200;
    private string message;
    private long srvtime = system.currenttimemillis();

    public baseresponse(string message) {
        this.message = message;
    }

    public baseresponse<t> setdata(t data) {
        this.data = data;
        return this;
    }

    public static <t> baseresponse<t> ok() {
        return new baseresponse<>("操作成功");
    }

    public static <t> baseresponse<t> ok(t data) {
        return new baseresponse<t>("操作成功").setdata(data);
    }

}

4 添加控制类

@controller
@requestmapping("/hello")
public class helloworld {

    // 此处数据从数据库中查询, 案例中也可以使用伪数据代替
    @autowired
    private usermapper usermapper;

    // {@code responseentity} 案列
    @getmapping("/one")
    @responsebody
    public user one() {

        list<user> users = usermapper.selectall();
        system.out.println(users.get(0));
        return users.get(0);
    }

    
    // {@code @responsebody}  案列
    @getmapping("/list")
    @responsebody
    public list<user> list() {

        list<user> users = usermapper.selectall();
        system.out.println(users);
        return users;
    }
}    

5 接口测试

浏览器访问: http://localhost:8080/hello/one

user(id=1, username=李子柒, phone=77777, icon=李子柒的头像, querytime=wed oct 27 20:47:02 cst 2021)
响应拦截成功

浏览器访问: http://localhost:8080/hello/list

[user(id=1, username=李子柒, phone=77777, icon=李子柒的头像, querytime=wed oct 27 20:46:58 cst 2021)]
响应拦截成功

ps: 如果直接响应字符串返回,则会报类型转换异常.

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