Question

我正在为OCPJWCD做准备。我有点卡在addHeader和setHeader方法上。我做理解差异，但当我试图在代码中实现它并检索值通过getHeaders（）或getHeader（）。它将值显示为null。我补充说这里的代码。有人可以检查并让我知道，到底出了什么问题。

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Created with IntelliJ IDEA.
 * User: Ben
 * Date: 7/14/13
 * Time: 1:51 PM
 * To change this template use File | Settings | File Templates.
 */
public class TestHeaderServlet extends HttpServlet {

  @Override
  protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
      throws ServletException, IOException {
    doPost(httpServletRequest,httpServletResponse);
  }


  @Override
  protected void doPost(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse)
      throws ServletException, IOException {
    httpServletResponse.setContentType("text/html");
    PrintWriter out = httpServletResponse.getWriter();
    httpServletResponse.setHeader("ben","value1");
    /*httpServletResponse.addHeader("ben","value1");
    httpServletResponse.addHeader("ben","value2");
    httpServletResponse.addHeader("ben","value3");
    httpServletResponse.addHeader("ben","value4");*/
    String value = httpServletRequest.getHeader("ben");
    out.println("value is: " + value)    ;
   /* Enumeration<String> enumeration = httpServletRequest.getHeaders("ben");
    while(enumeration.hasMoreElements()) {
      System.out.println("It has elements");

    }*/


  }
}

任何帮助都会很棒。

Answer 1

问题是您要将标头添加到response，并尝试从同一 HTTP请求 - 响应周期中的request对象中获取该标头。它不起作用，因为调用此Servlet的初始request没有此标头。它会被添加到response并发送回客户端，您无法从request对象中检索回来。如果您需要在response中设置内容并从request对象中检索回来，则可以使用Cookie。

addHeader（）和setHeader（）不起作用

1 个答案: