getWriter() has already been called for this response

这个错误通常表明您尝试从Spring MVC返回一个已使用的HttpServletResponse对象。

原因：这可能是由于直接调用HttpServletResponse的getWriter()或getOutputStream()方法，或者由于在控制器方法中抛出异常而自动调用HttpServletResponse的write()方法。

修改建议：您可以确保在控制器方法中没有调用任何HttpServletResponse的方法，并且不要在控制器方法中抛出异常。

规避建议：如果需要向客户端返回响应，请使用返回相应的对象，例如String、 ModelAndView或RedirectView。 此外，您还可以使用@ResponseStatus和@ExceptionHandler注解来处理异常情况，并生成适当的响应。

问题重现

ResponsePostInterceptor 里注入response.getWriter().write

package com.zhangziwa.practisesvr.interceptor;

import com.zhangziwa.practisesvr.utils.response.ResponseContext;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

@Component
public class ResponsePostInterceptor implements HandlerInterceptor {

	# 调用 response.getWriter().write
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.err.println("***ResponsePostInterceptor.preHandle***");
        response.setHeader("test-test", "test-test");
        response.getWriter().write("Response content");
        response.flushBuffer();
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.err.println("***ResponsePostInterceptor.postHandle***");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.err.println("***ResponsePostInterceptor.afterCompletion***");
        ResponseContext.clear();
    }
}

Controller 正常返回 ResponseEntity

    @RequestMapping(value = "/getAllStudents4", method = RequestMethod.GET)
    public ResponseEntity<List<Student>> getAllStudents4() {
        System.err.println("***Controller.getAllStudents4***");

        List<Student> students = userService.listStudents3(1, 5);
        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.add("test", "test");
        return ResponseEntity.ok().headers(httpHeaders).contentType(MediaType.APPLICATION_JSON).body(students);
    }

ResponseBodyAdvice 对 ResponseEntity进行增强

import org.springframework.core.MethodParameter;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
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;

import static java.util.Objects.nonNull;

@ControllerAdvice
public class ResponsePostAdvice implements ResponseBodyAdvice {


    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        System.err.println("***ResponsePostAdvice.supports***");
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class clazz, ServerHttpRequest request, ServerHttpResponse response) {
        System.err.println("***ResponsePostAdvice.beforeBodyWrite***");
        HttpHeaders headers = response.getHeaders();

        // 分页信息添加到ServerHttpResponse
        HttpHeaders headersContext = ResponseContext.getHeaders();

        if (nonNull(headersContext) && !headersContext.isEmpty()) {
            headersContext.forEach((key, values) -> values.forEach((value) -> {
                headers.addIfAbsent(key, value);
            }));
        }

        // 状态码添加到ServerHttpResponse
        if (nonNull(ResponseContext.getResponseCode())) {
            response.setStatusCode(ResponseContext.getResponseCode());
        }
        
        # 这里会报错
        return body;
    }
}

异常拦截GlobalExceptionHandler

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(Exception.class)
    @ResponseBody
    public ResponseEntity<String> handleException(Exception ex) {
        System.err.println("***GlobalExceptionHandler.handleException:" + ex.getMessage() + "***");
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("An error occurred");
    }

    @ExceptionHandler(NotFoundException.class)
    public ResponseEntity<String> handleNotFoundException(NotFoundException ex) {
        System.err.println("***GlobalExceptionHandler.handleNotFoundException***");
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body("Resource not found");
    }
}

调用路径分析

# 拦截器的preHandle （这里注入了response.getWriter().write）
***ResponsePostInterceptor.preHandle***
# Controller层
***Controller.getAllStudents4***

# ResponsePostAdvice进行增强后返回ServerHttpResponse
***ResponsePostAdvice.supports***
***ResponsePostAdvice.beforeBodyWrite***
## 这里报IllegalStateException了 被 @ControllerAdvice修饰的GlobalExceptionHandler 拦截到
***GlobalExceptionHandler.handleException:getWriter() has already been called for this response***

# 异常返回ResponseEntity 又被ResponsePostAdvice捕捉然后进行增强
***ResponsePostAdvice.supports***
***ResponsePostAdvice.beforeBodyWrite***
# 又报IllegalStateException，但是此时没被GlobalExceptionHandler 拦截
java.lang.IllegalStateException: getWriter() has already been called for this response
# 吃啥程序蹦了，故ResponsePostInterceptor.postHandle未执行。但是afterCompletion是否异常都会执行，所以执行了
***ResponsePostInterceptor.afterCompletion***

# 这里又执行一遍拦截器，但是未进入Controller层，不是很懂
***ResponsePostInterceptor.preHandle***
***ResponsePostInterceptor.postHandle***
***ResponsePostInterceptor.afterCompletion***