在 servlet 过滤器中向请求添加 HTTP 标头

Question

我正在与现有的 servlet 集成，该 servlet 从 HTTP 标头中提取一些属性。基本上，我正在实现一个无法访问实际请求的接口，它只能访问 HTTP 标头的 k->v 映射。

我需要传入一个请求参数。计划是使用 servlet 过滤器从参数到标头值，但当然 HttpServletRequest 对象没有 addHeader() 方法。

有什么想法吗？

Answer 1

扩展HttpServletRequestWrapper，覆盖头部getter也返回参数：

public class AddParamsToHeader extends HttpServletRequestWrapper {
    public AddParamsToHeader(HttpServletRequest request) {
        super(request);
    }

    public String getHeader(String name) {
        String header = super.getHeader(name);
        return (header != null) ? header : super.getParameter(name); // Note: you can't use getParameterValues() here.
    }

    public Enumeration getHeaderNames() {
        List<String> names = Collections.list(super.getHeaderNames());
        names.addAll(Collections.list(super.getParameterNames()));
        return Collections.enumeration(names);
    }
}

..并用它包装原始请求：

chain.doFilter(new AddParamsToHeader((HttpServletRequest) request), response);

---

也就是说，我个人认为这是个坏主意。而是让它直接访问参数或将参数传递给它。

Answer 2

您必须使用HttpServletRequestWrapper：

public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain) throws IOException, ServletException {
    final HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletRequestWrapper wrapper = new HttpServletRequestWrapper(httpRequest) {
        @Override
        public String getHeader(String name) {
            final String value = request.getParameter(name);
            if (value != null) {
                return value;
            }
            return super.getHeader(name);
        }
    };
    chain.doFilter(wrapper, response);
}

根据您想要做什么，您可能需要实现包装器的其他方法，例如 getHeaderNames。请注意，这是信任客户端并允许他们操作任何 HTTP 标头。您可能希望对它进行沙箱处理，并且只允许以这种方式修改某些标头值。

Answer 3

正如https://stackoverflow.com/users/89391/miku 指出的那样，这将是一个完整的 ServletFilter 示例，它使用同样适用于 Jersey 的代码添加 remote_addr 标头。

package com.bitplan.smartCRM.web;

import java.io.IOException;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

/**
 * 
 * @author wf
 * 
 */
public class RemoteAddrFilter implements Filter {

    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        HeaderMapRequestWrapper requestWrapper = new HeaderMapRequestWrapper(req);
        String remote_addr = request.getRemoteAddr();
        requestWrapper.addHeader("remote_addr", remote_addr);
        chain.doFilter(requestWrapper, response); // Goes to default servlet.
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    // https://stackoverflow.com/questions/2811769/adding-an-http-header-to-the-request-in-a-servlet-filter
    // http://sandeepmore.com/blog/2010/06/12/modifying-http-headers-using-java/
    // http://bijubnair.blogspot.de/2008/12/adding-header-information-to-existing.html
    /**
     * allow adding additional header entries to a request
     * 
     * @author wf
     * 
     */
    public class HeaderMapRequestWrapper extends HttpServletRequestWrapper {
        /**
         * construct a wrapper for this request
         * 
         * @param request
         */
        public HeaderMapRequestWrapper(HttpServletRequest request) {
            super(request);
        }

        private Map<String, String> headerMap = new HashMap<String, String>();

        /**
         * add a header with given name and value
         * 
         * @param name
         * @param value
         */
        public void addHeader(String name, String value) {
            headerMap.put(name, value);
        }

        @Override
        public String getHeader(String name) {
            String headerValue = super.getHeader(name);
            if (headerMap.containsKey(name)) {
                headerValue = headerMap.get(name);
            }
            return headerValue;
        }

        /**
         * get the Header names
         */
        @Override
        public Enumeration<String> getHeaderNames() {
            List<String> names = Collections.list(super.getHeaderNames());
            for (String name : headerMap.keySet()) {
                names.add(name);
            }
            return Collections.enumeration(names);
        }

        @Override
        public Enumeration<String> getHeaders(String name) {
            List<String> values = Collections.list(super.getHeaders(name));
            if (headerMap.containsKey(name)) {
                values.add(headerMap.get(name));
            }
            return Collections.enumeration(values);
        }

    }

}

web.xml sn-p:

<!--  first filter adds remote addr header -->
<filter>
    <filter-name>remoteAddrfilter</filter-name>
    <filter-class>com.bitplan.smartCRM.web.RemoteAddrFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>remoteAddrfilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>