如何发送请求并继续响应，并发送回客户端？

Question

客户端通过HTTP请求（通过浏览器post）调用Servlet，然后Servlet应向外部网站发送请求（get），并从网站接收响应（post）。servlet继续响应并向客户端发送响应（post）。

我的问题是如何在Servlet中发送和接收请求/响应并将某些内容发送回客户端？

Answer 1

URL url = new URL(urlString);
HttpURLConnection c = (HttpURLConnection)url.openConnection();  //connecting to url
c.setRequestMethod("GET");
BufferedReader in = new BufferedReader(new InputStreamReader(c.getInputStream()));  //stream to resource
String str;
while ((str = in.readLine()) != null)   //reading data
    responsestring += str+"\n";//process the response and save it in some string or so
in.close();  //closing stream
response.getWriter().write(responsestring);

Answer 2

您可以在以下表单中使用请求的set属性：<代码>请求。setAttribute（字符串键，对象值）。

示例：

public class FindPerson extends HttpServlet {

    // ... doGet implementation

    @Override
    protected void doPost( HttpServletRequest request, HttpServletResponse response )
            throws ServletException, IOException {

        // data to send to the client
        String name = "John White";
        int age = 54;



        // Adding attributes to the request
        request.setAttribute( "personName", name );
        request.setAttribute( "personAge", age );

        // Sending the result to the.jsp page
        getServletContext().getRequestDispatcher( "/WEB-INF/result.jsp" ).forward( request, response );

        }
    }
}

之后，您可以使用JSTL在JSP页面上读取此数据：

<p>Name: ${ requestScope.personName } </p>
<p>Age: ${ requestScope.personAge } </p>

其中，人名和人物是地图的关键。您可以使用请求设置它们。setAttribute。

！！！已更新！！！

在您的情况下，您将调用其他servlet，这些servlet将执行对外部站点的请求等。所有这些（从处理这些数据的外部站点收集数据）都将被放置，而不是设置名称和年龄值的代码（参见上面的示例）。希望有帮助！

Answer 3

您可以首先创建URL，然后使用URLConnection对象连接并接收响应，如下所示，以获取请求/响应

URL url = new URL(urlString);
HttpURLConnection c = (HttpURLConnection)url.openConnection();  //connecting to url
c.setRequestMethod("GET");
BufferedReader in = new BufferedReader(new InputStreamReader(c.getInputStream()));  //stream to resource
String str;
while ((str = in.readLine()) != null)   //reading data
   responsestring += str+"\n";//process the response and save it in some string or so
in.close();  //closing stream
response.getWriter().write(responsestring);

更新POST请求/响应执行此操作

URL obj = new URL(url);
HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

con.setRequestMethod("POST");

String urlParameters = ..;

con.setDoOutput(true);
DataOutputStream wr = new DataOutputStream(con.getOutputStream());
wr.writeBytes(urlParameters);
wr.flush();
wr.close();

BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
String inputLine;
StringBuffer res = new StringBuffer();

while ((inputLine = in.readLine()) != null) {
    res.append(inputLine);
}
in.close();
//process response
response.getWriter().write(res);