在之前的文章中介绍过Spring Boot开发中统一修改http响应体内容的方法，今天给大家再介绍另一种方案也能实现同样的效果，那就是JavaEE中通过使用Filter过滤器来修改http响应体~

工作原理

JavaEE中提供了HttpServletResponseWrapper，该类实现了HttpServletResponse接口，通过重写该类的getOutputStream、getWriter方法来拦截Servlet响应内容，结合Filter的使用，就可以在Filter中统一修改http响应体了
JavaEE官方文档说明：https://docs.oracle.com/javaee/7/api/javax/servlet/http/HttpServletResponseWrapper.html

使用方式

1. 编写HttpServletResponseWrapper的实现类，来包装HttpServletResponse，等下在Filter中会用于替换真正的HttpServletResponse对象

示例代码：https://github.com/netbuffer/javaee-demo/blob/master/src/main/java/cn/netbuffer/filter/wrapper/ModifyHttpResponseWrapper.java

public class ModifyHttpResponseWrapper extends HttpServletResponseWrapper {

    private CharArrayWriter bufferWriter;
    private ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    private HttpServletResponse httpServletResponse;

    public ModifyHttpResponseWrapper(HttpServletResponse response) {
        super(response);
        bufferWriter = new CharArrayWriter();
        httpServletResponse = response;
    }

    @Override
    public ServletOutputStream getOutputStream() {
        return new ServletOutputStreamWrapper(this.byteArrayOutputStream, this.httpServletResponse);
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        return new PrintWriter(bufferWriter);
    }

    public String getResult() {
        return bufferWriter.toString();
    }

    public String getContent() {
        return new String(byteArrayOutputStream.toByteArray());
    }

    @Override
    public void setContentType(String type) {
        super.setContentType(type);
    }

    private class ServletOutputStreamWrapper extends ServletOutputStream {

        private ByteArrayOutputStream outputStream;
        private HttpServletResponse response;

        public ServletOutputStreamWrapper(ByteArrayOutputStream byteArrayOutputStream, HttpServletResponse response) {
            this.outputStream = byteArrayOutputStream;
            this.response = response;
        }

        @Override
        public boolean isReady() {
            return true;
        }

        @Override
        public void setWriteListener(WriteListener listener) {
        }

        @Override
        public void write(int b) throws IOException {
            this.outputStream.write(b);
        }

        @Override
        public void flush() throws IOException {
            if (!this.response.isCommitted()) {
                byte[] body = this.outputStream.toByteArray();
                ServletOutputStream outputStream = this.response.getOutputStream();
                outputStream.write(body);
                outputStream.flush();
            }
        }
    }
}

2. 编写Filter过滤器来拦截http响应，达到最终修改http响应体的目的
   示例代码：https://github.com/netbuffer/javaee-demo/blob/master/src/main/java/cn/netbuffer/filter/ModifyHttpResponseFilter.java

@WebFilter(filterName = "ModifyHttpResponseFilter", urlPatterns = {"/json/*"})
public class ModifyHttpResponseFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
        ModifyHttpResponseWrapper modifyHttpResponseWrapper = new ModifyHttpResponseWrapper(httpServletResponse);
        System.out.println("-----------------before ModifyHttpResponseFilter------------------");
        filterChain.doFilter(servletRequest, modifyHttpResponseWrapper);
        System.out.println("-----------------after ModifyHttpResponseFilter------------------");
        JSONObject jsonObject = JSON.parseObject(StringUtils.isBlank(modifyHttpResponseWrapper.getResult()) ? modifyHttpResponseWrapper.getContent() : modifyHttpResponseWrapper.getResult());
        jsonObject.put("msg", "wrapper[" + jsonObject.getString("msg") + "]");
        HttpServletResponse response = (HttpServletResponse) modifyHttpResponseWrapper.getResponse();
        response.setContentType("application/json; charset=UTF-8");
        PrintWriter printWriter = response.getWriter();
        printWriter.write(jsonObject.toJSONString());
        printWriter.flush();
        printWriter.close();
    }

    @Override
    public void destroy() {
    }

}

3. 编写测试用的Servlet，来测试http响应体改写情况
   完整示例代码：https://github.com/netbuffer/javaee-demo/blob/master/src/main/java/cn/netbuffer/servlet/JSONServlet.java

@WebServlet(name = "jsonServlet", urlPatterns = {"/json"})
public class JSONServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        JSONObject data = new JSONObject();
        data.put("success", true);
        data.put("msg", "invoke success for " + this.getClass().getName());
        System.out.println("get json=" + data);
        response.getWriter().write(data.toString());
    }

}

运行效果

启动工程，使用Postman工具访问/json接口测试
可以看到返回的数据中已经被wrapper[]包装了

请求执行流程

完整测试工程请参考：https://github.com/netbuffer/javaee-demo

明白了原理，JavaEE中的这种机制我们完全可以用在Spring Boot开发中~
示例伪代码：

     //注册Filter过滤器来拦截响应内容，并修改最终的响应体
    @Bean
    public FilterRegistrationBean registration() {
        FilterRegistrationBean registration = new FilterRegistrationBean();
        //注册
        registration.setFilter(new YourFilter());
        registration.addUrlPatterns("/YourPath/*");
        registration.setOrder(1000);
        return registration;
    }

示例过滤器，在doFilter中做自定义的逻辑处理，可以达到统一修改http响应体的效果~

  public class YourFilter extends GenericFilterBean {

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
       //todo 自定义处理逻辑
    }

  }

完整代码写法可以参考我在spring-boot-admin issue中的回答：https://github.com/codecentric/spring-boot-admin/issues/1053#issuecomment-920630443