解析springboot包装controller返回值问题

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我是靠谱客的博主拼搏火龙果，这篇文章主要介绍解析springboot包装controller返回值问题，现在分享给大家，希望可以做个参考。

1、springboot项目统一包装返回值，通常返回结果包含code、message、data，结构如下

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import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
 
@Data
@NoArgsConstructor
@AllArgsConstructor
public class ResponseResult<T> {
    private int code;
    private String message;
    private T data;
 
    public ResponseResult(T data) {
        this.data = data;
        this.code = 0;
        this.message = "success";
    }
}

2、基于ControllerAdvice和HttpMessageConverter实现

定义类ResponseAdvisor实现ResponseBodyAdvice接口，重写supports跟beforeBodyWrite方法

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import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;
 
@ControllerAdvice
public class ResponseAdvisor implements ResponseBodyAdvice<Object> {
    @Override
    public boolean supports(MethodParameter methodParameter, Class<? extends HttpMessageConverter<?>> aClass) {
        return true;
    }
 
    @Override
    public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType,
                                  Class<? extends HttpMessageConverter<?>> aClass, ServerHttpRequest serverHttpRequest,
                                  ServerHttpResponse serverHttpResponse) {
        if(o instanceof ResponseResult){
            return o;
        }
        return new ResponseResult<>(o);
    }

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import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;
 
@ControllerAdvice
public class ResponseAdvisor implements ResponseBodyAdvice<Object> {
    @Override
    public boolean supports(MethodParameter methodParameter, Class<? extends HttpMessageConverter<?>> aClass) {
        return true;
    }
 
    @Override
    public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType,
                                  Class<? extends HttpMessageConverter<?>> aClass, ServerHttpRequest serverHttpRequest,
                                  ServerHttpResponse serverHttpResponse) {
        if(o instanceof ResponseResult){
            return o;
        }
        return new ResponseResult<>(o);
    }

3、接口测试

3.1 测试返回Object类型：

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@RestController
@RequestMapping("/test")
public class TestController {
 
    @GetMapping("/test")
    public Test test(){
        return new Test("test", 10);
    }
}

执行结果如下：

3.2 测试返回String类型：

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@RestController
@RequestMapping("/test")
public class TestController {
 
    @GetMapping("/test")
    public Test test(){
        return new Test("test", 10);
    }
 
    @GetMapping("/test1")
    public String test1(){
        return "test";
    }
}

执行结果如下：

3.3 如果Controller类的返回值没有String类型的，仅有上面这个类就够了。如果有String类型的返回值，就有可能遇到类型不匹配的问题。HttpMessageConverter是根据Controller的原始返回值类型进行处理的，而我们在ResponseAdvisor中改变了返回值的类型。如果HttpMessageConverter处理的目标类型是Object还好说，如果是其它类型就会出现问题，其中最容易出现问题的就是String类型，因为在所有的HttpMessageConverter实例集合中，StringHttpMessageConverter要比其它的Converter排得靠前一些。我们需要尝试将处理Object类型的HttpMessageConverter放得靠前一些，这可以在一个Configuration类中完成：

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import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration;
 
import java.util.List;
 
@Configuration
public class ResponseResultConfig extends DelegatingWebMvcConfiguration {
    @Override
    protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(0, new MappingJackson2HttpMessageConverter());
        super.configureMessageConverters(converters);
    }
}