Tomcat 8.5 response.getWriter() 已为此响应调用

Question

我在生产环境中使用 Tomcat 8.5.23 和 Servlet（如果相关，具有 Spring 自动装配功能） response.getWriter() return null 生产中

在自定义过滤器中调用 chain.doFilter(req, res); 时也会发生这种情况：

public class MyFilter implements Filter {
  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) res;
        response.setHeader("Access-Control-Allow-Origin", "*");
        chain.doFilter(req, res);
  }
  public void init(FilterConfig filterConfig) {}
  public void destroy() {}
}

异常：

Request processing failed; nested exception is java.lang.IllegalStateException: getWriter() has already been called for this response] with root cause
java.lang.IllegalStateException: getWriter() has already been called for this response
        at org.apache.catalina.connector.Response.getOutputStream(Response.java:591)
        at org.apache.catalina.connector.ResponseFacade.getOutputStream(ResponseFacade.java:194)
        at org.springframework.http.server.ServletServerHttpResponse.getBody(ServletServerHttpResponse.java:89)
        at org.springframework.http.converter.StringHttpMessageConverter.writeInternal(StringHttpMessageConverter.java:106)
        at org.springframework.http.converter.StringHttpMessageConverter.writeInternal(StringHttpMessageConverter.java:41)
        at org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:227)
        at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:247)
        at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:203)
        at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:81)
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:113)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)

我尝试添加但没有成功

Answer 1

您的过滤器代码看起来没问题，问题出在其他地方。评论已经提到 getWriter() 不能 return null。查看出现这种情况的代码。有可能代码试图将 writer 分配给一个变量，但捕获并忽略了该异常。在异常被忽略之后，有人试图使用该变量，但它包含 null 因为赋值没有发生。

可能发生这些 "already called" 错误的一个常见情况是错误处理。一个 servlet 开始发送响应，因此称为 getWriter()。然后遇到错误，错误处理尝试写入错误响应，因此再次调用 getWriter()。您无法重现该问题，因为该错误情况是随机发生的。

Tomcat 8.5 response.getWriter() 已为此响应调用

Tomcat 8.5 response.getWriter() has already been called for this response

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servlet-filters

tomcat8.5