检查HTTP POST请求的内容类型到Java servlet

我编写了一个简单的servlet，它接受HTTP POST请求并发回一个简短的响应。 这是servlet的代码：

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 = ""; 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 + "" + strMessage + ""; 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 } } 

这是我用来发送请求的客户端：

 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 = ""; 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 } } 

我遇到的问题是，当我运行客户端程序时，我得到以下输出：

 Server says: 0Incorrect MIME type 

我试过调用request.getContentType（）并得到“text / xml”作为输出。 只是想弄清楚为什么字符串不匹配。

Answer 1

你用错误的方式比较字符串。

 if (strContentType != "text/xml") 

字符串不是原始字母 ，它们是对象 。 当使用!=来比较两个对象时，它只会测试它们是否指向相同的引用 。 但是，您对比较两个不同字符串引用的内容非常感兴趣，而不是它们指向相同的引用。

然后，您应该使用equals()方法 ：

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

或者，更好的是，如果Content-Type标头不存在（因此变为null ）， NullPointerException避免NullPointerException ：

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