tomcat - 使用 servlet 别名的遗留 servlet 链接

Question

我正在尝试使用 ServletExec 将现有应用程序从 IIS 迁移到 tomcat。除了有一个带有两个 servlet 的 servlet 链的情况外，我的一切都正常工作。

第一个 servlet 做一些处理，第二个 servlet 做一些翻译。

request-->ProcessServlet--> (untranslated html) -->TranslateServlet --> response

在我的例子中，我可以调用 ProcessServlet，它会生成带有未翻译标签的 html。第二个 servlet 看起来像是获取 html、定位众所周知的翻译标签并翻译它们并为浏览器生成可读的输出。

从谷歌搜索，看起来不再支持/推荐使用 servlet 别名的 servlet 链接(from this page)并且可以使用过滤器实现相同的功能，但类必须实现一个接口(interface)，但不幸的是，在我的情况下我必须工作与现有的类文件。

This page指定概念但没有示例。

同样来自 this page

How to Configure a Servlet Chain Using Servlet Aliasing

Using the Servlet Aliasing subsection of the setup section in the Administration Tool, a list of servlets can be named for a particular URL request. In the servlets table, when adding a new mapping, you are allowed to enter a comma-separated list of servlets in the order in which they should be invoked when a request arrives for that particular URL. This configures a servlet chain to be invoked every time a request that matches the URL arrives.

任何人都可以指定一个示例或为我指明正确的方向，以说明如何让这个链从 web.xml 开始工作吗？

更新:

根据 kschneid 在他的回答中的概述，这是对我有用的完整实现

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

public class TranslateFilter implements Filter {

  private FilterConfig config = null;

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

  public void destroy() {
    config = null;
  }

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

        HttpServletResponse httpResponse = (HttpServletResponse) response;
        MyHttpServletResponseWrapper processResponse  =   new MyHttpServletResponseWrapper(httpResponse);
        chain.doFilter(request, processResponse );
        String content = processResponse.toString();
        config.getServletContext().log("CONTENT: " + content);
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        MyHttpServletRequestWrapper processResponseAsRequest = new MyHttpServletRequestWrapper(httpRequest, content);

        RequestDispatcher dispatch = request.getRequestDispatcher("/Translate");
        response.setContentType("text/html");
        dispatch.forward(processResponseAsRequest, response); // forward to translate servlet with response from process servlet as the request and the original response
  }

}

class MyHttpServletResponseWrapper 
  extends HttpServletResponseWrapper {

  private StringWriter sw = new StringWriter();

  public MyHttpServletResponseWrapper(HttpServletResponse response) {
    super(response);
  }

  public PrintWriter getWriter() throws IOException {
    return new PrintWriter(sw);
  }

  public ServletOutputStream getOutputStream() throws IOException {
    throw new UnsupportedOperationException();
  }

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

class MyHttpServletRequestWrapper 
  extends HttpServletRequestWrapper {
    private String content;
    public MyHttpServletRequestWrapper(HttpServletRequest request) {
        super(request);
    }

    public MyHttpServletRequestWrapper(HttpServletRequest request, String content) {
        super(request);
        this.content = content;
    }

    public ServletInputStream getInputStream()
    {
        return new MyServletInputStream(content);
    }

    public BufferedReader getReader()
    {
        InputStreamReader in= new InputStreamReader(getInputStream());
        return new BufferedReader(in);
    }
  }

class MyServletInputStream extends ServletInputStream
{
    private InputStream is;

    public MyServletInputStream(String content)
    {
        is = new ByteArrayInputStream(content.getBytes());
    }

    public int read() throws IOException
    {
        return is.read();
    }
}

Answer 1

我不太熟悉 servlet 链接的实现细节，但这里有一个可能有效的通用方法。将两个 servlet 映射到不同的 URL:

<servlet-mapping>
    <servlet-name>process</servlet-name>
    <url-pattern>/process</url-pattern>
</servlet-mapping>

<servlet-mapping>
    <servlet-name>translate</servlet-name>
    <url-pattern>/translate</url-pattern>
</servlet-mapping>

然后将过滤器映射到 process servlet:

<filter-mapping>
    <filter-name>processChain</filter-name>
    <servlet-name>process</servlet-name>
</filter-mapping>

processChain 过滤器会执行如下操作:

public void doFilter(ServletRequest request,
                     ServletResponse response,
                     FilterChain chain) throws IOException, ServletException {
    ServletResponseWrapper processResponse = ...; // response buffer
    chain.doFilter(request, processResponse); // let process servlet populate response buffer
    ServletRequestWrapper processResponseAsRequest = ...; // use processResponse to create request for translate servlet
    RequestDispatcher dispatch = request.getRequestDispatcher("/translate");
    dispatch.forward(processResponseAsRequest, response); // forward to translate servlet with response from process servlet as the request and the original response
}

...或类似的东西 ;)