查找使用servlet过滤器将内容插入响应的示例 [英] Looking for an example for inserting content into the response using a servlet filter

问题描述

我一直在搜索net和stackoverflow，以获取使用servlet过滤器将内容插入响应的示例，但只能找到捕获/压缩输出和/或更改标头的人的示例。我的目标是在所有HTML响应的结束之前附加一大块HTML。

I've been searching the net and stackoverflow for an example of somebody inserting content into the response using a servlet filter, but can only find examples of people capturing/compressing the output and/or changing the headers. My goal is to append a chunk of HTML just before the closing </body> of all HTML responses.

我正在开发一个扩展HttpServletResponseWrapper以使用的解决方案我自己的PrintWriter，然后覆盖其上的写入方法。在write方法中，我存储了最后7个字符，看它是否等于关闭body标签，然后我写了我的HTML块加上关闭的body标签，然后继续对文档的其余部分进行正常的写操作。

I'm working on a solution that extends the HttpServletResponseWrapper to use my own PrintWriter, then overriding the write methods thereon. Inside the write method I'm storing the last 7 characters to see if it's equal to the closing body tag, and then I write my HTML chunk plus the closing body tag, before continuing normal write operations for the rest of the document.

我觉得有人必须已经解决了这个问题，而且可能比我更优雅。我很感激如何使用servlet过滤器将内容插入响应中的任何示例。

I feel that somebody must have solved this problem already, and probably more elegantly than I will. I'd appreciate any examples of how to use a servlet filter to insert content into a response.

更新

回应评论，我也试图从 http：//实施CharResponseWrapper www.oracle.com/technetwork/java/filters-137243.html 。这是我的代码：

Responding to a comment, I am also trying to implement the CharResponseWrapper from http://www.oracle.com/technetwork/java/filters-137243.html. Here is my code:

PrintWriter out = response.getWriter();
CharResponseWrapper wrappedResponse = new CharResponseWrapper(
        (HttpServletResponse)response);

chain.doFilter(wrappedRequest, wrappedResponse);
String s = wrappedResponse.toString();

if (wrappedResponse.getContentType().equals("text/html") &&
        StringUtils.isNotBlank(s)) {
    CharArrayWriter caw = new CharArrayWriter();
    caw.write(s.substring(0, s.indexOf("</body>") - 1));
    caw.write("WTF</body></html>");
    response.setContentLength(caw.toString().length());
    out.write(caw.toString());
}
else {
    out.write(wrappedResponse.toString());
}

out.close();

我也在处理请求，但该代码有效且不应影响响应。

I am also wrapping the request, but that code works and shouldn't affect the response.

推荐答案

我正在使用的代码库在处理响应时调用getOutputStream方法而不是getWriter，因此其他示例包含在另一个中答案没有用。这是一个更完整的答案，适用于OutputStream和PrintWriter，如果写入器被访问两次，甚至可以正确地出错。这源于一个很好的例子， DUMP REQUEST和响应使用JAVAX.SERVLET.FILTER 。

The codebase I am using, calls the getOutputStream method, instead of getWriter when it processes the response, so the examples included in the other answer doesn't help. Here is a more complete answer that works with both the OutputStream and the PrintWriter, even erroring correctly, if the writer is accessed twice. This is derived from the great example, DUMP REQUEST AND RESPONSE USING JAVAX.SERVLET.FILTER.

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class MyFilter implements Filter
{
    private FilterConfig filterConfig = null;

    private static class ByteArrayServletStream extends ServletOutputStream
    {
        ByteArrayOutputStream baos;

        ByteArrayServletStream(ByteArrayOutputStream baos)
        {
            this.baos = baos;
        }

        public void write(int param) throws IOException
        {
            baos.write(param);
        }
    }

    private static class ByteArrayPrintWriter
    {

        private ByteArrayOutputStream baos = new ByteArrayOutputStream();

        private PrintWriter pw = new PrintWriter(baos);

        private ServletOutputStream sos = new ByteArrayServletStream(baos);

        public PrintWriter getWriter()
        {
            return pw;
        }

        public ServletOutputStream getStream()
        {
            return sos;
        }

        byte[] toByteArray()
        {
            return baos.toByteArray();
        }
    }

    public class CharResponseWrapper extends HttpServletResponseWrapper
    {
        private ByteArrayPrintWriter output;
        private boolean usingWriter;

        public CharResponseWrapper(HttpServletResponse response)
        {
            super(response);
            usingWriter = false;
            output = new ByteArrayPrintWriter();
        }

        public byte[] getByteArray()
        {
            return output.toByteArray();
        }

        @Override
        public ServletOutputStream getOutputStream() throws IOException
        {
            // will error out, if in use
            if (usingWriter) {
                super.getOutputStream();
            }
            usingWriter = true;
            return output.getStream();
        }

        @Override
        public PrintWriter getWriter() throws IOException
        {
            // will error out, if in use
            if (usingWriter) {
                super.getWriter();
            }
            usingWriter = true;
            return output.getWriter();
        }

        public String toString()
        {
            return output.toString();
        }
    }

    public void init(FilterConfig filterConfig) throws ServletException
    {
        this.filterConfig = filterConfig;
    }

    public void destroy()
    {
        filterConfig = null;
    }

    public void doFilter(
            ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException
    {
        CharResponseWrapper wrappedResponse = new CharResponseWrapper(
                (HttpServletResponse)response);

        chain.doFilter(request, wrappedResponse);
        byte[] bytes = wrappedResponse.getByteArray();

        if (wrappedResponse.getContentType().contains("text/html")) {
            String out = new String(bytes);
            // DO YOUR REPLACEMENTS HERE
            out = out.replace("</head>", "WTF</head>");
            response.getOutputStream().write(out.getBytes());
        }
        else {
            response.getOutputStream().write(bytes);
        }
    }
}

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