查找使用 servlet 过滤器将内容插入响应的示例

java servlet-filters tomcat6

2022-09-01 05:52:12

我一直在搜索net和stackoverflow，寻找一个人使用servlet过滤器将内容插入响应的示例，但只能找到人们捕获/压缩输出和/或更改标头的示例。我的目标是在所有 HTML 响应的结束</正文之前附加一块 HTML>。

我正在研究一个解决方案，该解决方案将HttpServletResponseWrapper扩展到使用我自己的PrintWriter，然后覆盖其上的写入方法。在 write 方法中，我存储最后 7 个字符以查看它是否等于结束正文标记，然后编写我的 HTML 块和结束正文标记，然后继续对文档的其余部分执行正常的写入操作。

我觉得一定有人已经解决了这个问题，而且可能比我更优雅。我很感激任何如何使用 servlet 过滤器将内容插入响应的示例。

更新

作为对评论的回应，我还试图从 http://www.oracle.com/technetwork/java/filters-137243.html 实现CharResponseWrapper。这是我的代码：

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();

我也包装了请求，但该代码有效，不应影响响应。

答案 1

我正在使用的代码库在处理响应时调用 getOutputStream 方法，而不是 getWriter，因此其他答案中包含的示例没有帮助。下面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，甚至错误正确。这是从一个很好的例子，使用JAVAX的转储请求和响应中派生出来的。SERVLET.过滤器。

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);
        }
    }
}

答案 2

您需要实现 HttpServletResponseWrapper 来修改响应。请参阅此文档过滤器的要点，它有一个转换响应的示例，这超出了您的要求

编辑

我尝试了一个简单的Servlet与响应过滤器，它工作得很好。Servlet输出字符串，响应过滤器将字符串附加到其中，最后当我从浏览器运行时，我得到的响应是你试图实现的。TestfilteredTest filtered

我确实在Apache Tomcat 7上运行了以下代码，并且它无一例外地工作。

Servlet：

protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {

   response.getWriter().println("Test");

}

滤波器：

public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {

    System.out.println("BEFORE filter");
    PrintWriter out = response.getWriter();
    CharResponseWrapper responseWrapper = new CharResponseWrapper(
            (HttpServletResponse) response);

    chain.doFilter(request, responseWrapper);

    String servletResponse = new String(responseWrapper.toString());

    out.write(servletResponse + " filtered"); // Here you can change the response


    System.out.println("AFTER filter, original response: "
            + servletResponse);

}

CharResponseWrapper（与文章完全相同）

public class CharResponseWrapper extends HttpServletResponseWrapper {
    private CharArrayWriter output;

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

    public CharResponseWrapper(HttpServletResponse response) {
        super(response);
        output = new CharArrayWriter();
    }

    public PrintWriter getWriter() {
        return new PrintWriter(output);
    }
}

网.xml

<servlet>
    <servlet-name>TestServlet</servlet-name>
    <servlet-class>TestServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>TestServlet</servlet-name>
    <url-pattern>/TestServlet</url-pattern>
</servlet-mapping>

<filter>
    <filter-name>TestFilter</filter-name>
    <filter-class>MyFilter</filter-class>
</filter>

<filter-mapping>
    <filter-name>TestFilter</filter-name>
    <url-pattern>/TestServlet/*</url-pattern>
</filter-mapping>