Question

这是Java代码使用套接字从C服务器接收数据并将数据存储在Google Data Store中并在Google App Engine上部署应用程序。

package pack.exp;

@SuppressWarnings("serial")
public class CToJavaToCloudServlet extends HttpServlet 
{
static List<String> obj1; 

public static void main(String[] args) throws UnknownHostException, IOException 
{
        Socket s = new Socket("10.9.11.55", 6870);
    InputStream stream = s.getInputStream();
    byte[] data = new byte[13];
    int read;
    String can_Id= null;


    while((read = stream.read(data)) != -1)
    {
        can_Id= String.format("%02X%02X%02X%02X", data[0], data[1], data[2],    
            data[3]);

    String can_Data= String.format("%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X", 
            data[4], data[5], data[6], data[7], data[8], data[9], data[10], data[11]);

    obj1= new ArrayList<String>();
    obj1.add(can_Data.substring(0, 2));
    obj1.add(can_Data.substring(3, 5));
    obj1.add(can_Data.substring(6, 8));
    obj1.add(can_Data.substring(9, 11));
    obj1.add(can_Data.substring(12, 14));
    obj1.add(can_Data.substring(15, 17));
    obj1.add(can_Data.substring(18, 20));
    obj1.add(can_Data.substring(21, 23));
    }
}

public void doGet(HttpServletRequest req, HttpServletResponse resp) throws 
           IOException 
{
    Key k1 = KeyFactory.createKey("C","0C F0 0400"); 

    String statusEEC1= obj1.get(0);
    String driversDemandEnginePercentTorque= obj1.get(1);
    String actualEnginePercentTorque= obj1.get(2);
    String engineSpeed= obj1.get(3) + obj1.get(4);
    String sourceAddressOfControllingDeviceForEngineControl= obj1.get(5);
    String engineStarterMode= obj1.get(6);
    String engineDemandPercentTorque= obj1.get(7); 

    Entity can1 = new Entity(k1);

    can1.setProperty("Status EEC", statusEEC1);     

            can1.setProperty("Drivers Demand Engine Percent Torque", 
            driversDemandEnginePercentTorque); 

            can1.setProperty("Actual Engine Percent Torque", 
            actualEnginePercentTorque);

            can1.setProperty("Engine Speed", engineSpeed);

            can1.setProperty("Source Address Of Controlling Device For Engine Control", 
            sourceAddressOfControllingDeviceForEngineControl);

            can1.setProperty("Engine Starter Mode", engineStarterMode);

            can1.setProperty("Engine Demand Percent Torque", 
            engineDemandPercntTorque);


    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
    datastore.put(can1);

    Entity can11 = null;

    try 
    {
        can11= datastore.get(k1);
    }

    catch (EntityNotFoundException e) 
    {
        e.printStackTrace();
    }


    String statusEEC11= (String) can11.getProperty("Status EEC");

            String driversDemandEnginePercentTorque1= (String) 
            can11.getProperty("Drivers Demand Engine Percent Torque");

            String actualEnginePercentTorque1= (String) can11.getProperty("Actual 
            Engine Percent Torque");

            String engineSpeed1= (String) can11.getProperty("Engine Speed");

            String sourceAddressOfControllingDeviceForEngineControl1= (String)  
            can11.getProperty("Source Address Of Controlling Device For Engine  
            Control");
    String engineStarterMode1= (String) can11.getProperty("Engine Starter 
            Mode");
    String engineDemandPercentTorque1= (String) can11.getProperty("Engine 
            Demand Percent Torque");


    resp.setContentType("text/plain");
    resp.getWriter().println("Can id 0C F0 0400------>");
    resp.getWriter().println("");
    resp.getWriter().println("Status EEC--- " + statusEEC11);  
    resp.getWriter().println("Drivers Demand Engine Percent Torque---" +  
            driversDemandEnginePercentTorque1);  
    resp.getWriter().println("Actual Engine Percent Torque---" + 
            actualEnginePercentTorque1);  
    resp.getWriter().println("Engine Speed---" + engineSpeed);  
    resp.getWriter().println("Source Address Of Controlling Device For Engine 
            Control---" + sourceAddressOfControllingDeviceForEngineControl1);  
    resp.getWriter().println("Engine Starter Mode---" + engineStarterMode1); 
    resp.getWriter().println("Engine Demand Percent Torque---" +                 
            engineDemandPercentTorque1); 
    resp.getWriter().println("");
    resp.getWriter().println("");
    resp.getWriter().println("");
    resp.getWriter().println("");
   }
}

在将应用部署到Google云引擎时，我收到了错误消息。该网站无法显示该页面 HTTP 500 最可能的原因： •网站正在维护中。 •网站出现编程错误。

任何人都可以帮我解决这个问题。

Answer 1

javax.servlet和javax.servlet.http包提供了用于编写servlet的接口和类。所有servlet都必须实现Servlet接口，该接口定义了生命周期方法。实现通用服务时，可以使用或扩展随Java Servlet API提供的GenericServlet类。 HttpServlet类提供了用于处理特定于HTTP的服务的方法，例如doGet和doPost。

由于您要实施HttpServlet界面，因此必须实施doGet和/或doPost。

Servlet init方法允许servlet在处理请求之前执行一次性初始化。实现init方法时的一个常见错误是以这种形式：

因此根本不会调用您的main方法。将代码从main移动到init。您的代码的另一个问题是您正在打开期望数据的套接字。这应该在doGet和/或doPost方法中完成，因为它们负责接收数据。

HTTP 500网站无法显示页面

1 个答案: