檢查HTTP POST請求的內容類型到Java servlet

Question

我寫了一個簡單的servlet，它接受HTTP POST請求併發送一個簡短的響應。下面是該servlet代碼：

import java.io.BufferedInputStream; 
import java.io.ByteArrayInputStream; 
import java.io.IOException; 
import java.io.InputStream; 

import javax.servlet.ServletException; 
import javax.servlet.ServletOutputStream; 
import javax.servlet.annotation.WebServlet; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

import org.apache.commons.logging.*; 

/** 
* Servlet implementation class MapleTAServlet 
*/ 
@WebServlet(description = "Receives XML request text containing grade data and returns  response in XML", urlPatterns = { "/MapleTAServlet" }) 
public class MapleTAServlet extends HttpServlet { 
    private static final long serialVersionUID = 1L; 
    private Log log = LogFactory.getLog(MapleTAServlet.class); 

    /** 
    * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 
    */ 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {  
     String strXMLResponse = "<Response><code>"; 
     String strMessage = ""; 
     int intCode = 0; 
     ServletOutputStream stream = null; 
     BufferedInputStream buffer = null; 

    try 
    { 
     String strContentType = request.getContentType(); 

     // Make sure that the incoming request is XML data, otherwise throw up a red flag 
     if (strContentType != "text/xml") 
     { 
      strMessage = "Incorrect MIME type"; 
     } 
     else 
     { 
      intCode = 1;   
     } // end if 

     strXMLResponse += intCode + "</code><message>" + strMessage + "</message></Response>"; 

     response.setContentType("text/xml"); 
     response.setContentLength(strXMLResponse.length()); 

     int intReadBytes = 0; 

     stream = response.getOutputStream(); 

     // Converts the XML string to an input stream of a byte array 
     ByteArrayInputStream bs = new ByteArrayInputStream(strXMLResponse.getBytes()); 
     buffer = new BufferedInputStream(bs); 

     while ((intReadBytes = buffer.read()) != -1) 
     { 
      stream.write(intReadBytes); 
     } // end while 
    } 
    catch (IOException e) 
    { 
     log.error(e.getMessage()); 
    } 
    catch (Exception e) 
    { 
     log.error(e.getMessage()); 
    } 
    finally 
    { 
     stream.close(); 
     buffer.close(); 
    } // end try-catch 

    } 

} 

而這裏的，我使用發送請求的客戶端：

import java.net.HttpURLConnection; 
import java.net.URL; 
import java.io.*; 

public class TestClient 
{ 

    /** 
    * @param args 
    */ 
    public static void main(String[] args) 
    { 
     BufferedReader inStream = null; 

     try 
      { 
     // Connect to servlet 
     URL url = new URL("http://localhost/mapleta/mtaservlet"); 
     HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 

     // Initialize the connection 
     conn.setDoOutput(true); 
     conn.setDoInput(true); 
     conn.setRequestMethod("POST"); 
     conn.setUseCaches(false); 
     conn.setRequestProperty("Content-Type", "text/xml"); 
     //conn.setRequestProperty("Connection", "Keep-Alive"); 

     conn.connect(); 

     OutputStream out = conn.getOutputStream(); 

     inStream = new BufferedReader(new InputStreamReader(conn.getInputStream())); 

     String strXMLRequest = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><Request></Request>"; 
     out.write(strXMLRequest.getBytes()); 
     out.flush(); 
     out.close(); 

     String strServerResponse = ""; 

     System.out.println("Server says: "); 
     while ((strServerResponse = inStream.readLine()) != null) 
     { 
      System.out.println(strServerResponse); 
     } // end while 

     inStream.close(); 
     } 
     catch (IOException e) 
     { 
      e.printStackTrace(); 
     } 
     catch (Exception e) 
     { 
      e.printStackTrace(); 
     } // end try catch 
    } 
} 

我遇到的問題是，當我運行客戶端程序，我得到以下輸出：

Server says: 
<Response><code>0</code><message>Incorrect MIME type</message></Response> 

我已經打過電話request.getContentType（），並已經得到了「文本/ XML」作爲輸出。試圖找出爲什麼字符串不匹配。

Answer 1

你正在比較字符串的方式是錯誤的。

if (strContentType != "text/xml") 

Strings不primitives，他們是objects。當使用!=來比較兩個對象時，它只會測試它們是否不指向相同的參考。但是，您比較兩個不同字符串引用的內容，而不是如果它們指向相同的引用。

那麼你應該使用the equals() method此：

if (!strContentType.equals("text/xml")) 

或者，更好，避免NullPointerException如果Content-Type頭不存在（並因此成爲null）：

if (!"text/xml".equals(strContentType))