原因是在我们伪造的响应（`CachedHttpServletResponse` ），覆写了getWriter();，只能获取一次，在模板引擎渲染时，需要再次获取writer()。

我的解决方法是，将Pritwer和ServletOutpuStream存一个副本到CachedHttpServletResponse中，在构造方法时，初始化这两个值。

public class CachedHttpServletResponseBackup extends HttpServletResponseWrapper {    private ByteArrayOutputStream output = new ByteArrayOutputStream();//    private boolean open = false;    private PrintWriter cacheWriter;    private ServletOutputStream cacheOut;    public CachedHttpServletResponseBackup(HttpServletResponse response) throws UnsupportedEncodingException {        super(response);        cacheOut = new ServletOutputStream() {            @Override            public boolean isReady() {                return true;            }            @Override            public void setWriteListener(WriteListener writeListener) {            }            @Override            public void write(int b) throws IOException {                output.write(b);            }        };        cacheWriter = new PrintWriter(output, false);    }    @Override    public PrintWriter getWriter()   {        return cacheWriter;    }    @Override    public ServletOutputStream getOutputStream() throws IOException {        return cacheOut;    }    public byte[] getContent(){        return output.toByteArray();    }}

对应的CacheFilter中也要修改成CachedHttpServletResponseBackup