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
- 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
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();
}
}
}
}
- 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() {
}
}
- 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
