Wie Sie Entitäten aus dem Datenspeicher mithilfe von pojo abrufen?

Question

package com.myproj; 

    import java.io.IOException; 
    import java.io.PrintWriter; 
    import java.util.List; 

    import javax.jdo.PersistenceManager; 
    import javax.jdo.Query; 
    import javax.servlet.ServletException; 
    import javax.servlet.http.HttpServlet; 
    import javax.servlet.http.HttpServletRequest; 
    import javax.servlet.http.HttpServletResponse; 


    public class Retrieve extends HttpServlet{ 
    /** 
    * 
    */ 
    private static final long serialVersionUID = 1L; 

    public void doGet(HttpServletRequest request,HttpServletResponse response)     throws ServletException, IOException 
    { 
     response.setContentType("text/html"); 

     PrintWriter out = response.getWriter(); 
     PersistenceManager pm= PMF.get().getPersistenceManager(); 
     Query q = pm.newQuery("SELECT * FROM REGISTER"); 

     @SuppressWarnings("unchecked") 
     List<Register> ls = (List<Register>) q.execute(); 
     for (Register result : ls) 
     { 
      String firstName = (String) result.getName(); 
      String email = (String) result.getEmail(); 

      out.println(firstName + " " + email); 
      } 
     } 
    } 


package com.myproj; 
import javax.jdo.annotations.PersistenceCapable; 
import javax.jdo.annotations.Persistent; 

@PersistenceCapable 
public class Register { 
@Persistent 
protected String Name; 
public String getName() { 
return Name; 
} 

public void setName(String Name) { 
this.Name = Name; 
} 

@Persistent 
protected String UName; 
public String getUName() { 
return UName; 
} 

public void setLName(String UName) { 
this.UName = UName; 
} 

@Persistent 
protected String email; 
public String getEmail() { 
return email; 
} 

public void setEmail(String email) { 
this.email = email; 
} 

@Persistent 
protected String pass; 
public String getPass() { 
return pass; 
} 

public void setPass(String pass) { 
this.pass = pass; 
} 
} 

wo Register meine pojo Klasse ist, wenn ich versuche, das ich die INTERNAL_SERVER_ERROR durch die Nullpointer verursacht bekommen auszuführen und i dono den Code alle Details von der Einheit im Voraus Art dank abrufen

Answer 1

Sie verwenden sollten, pm.getObjectById (Register.class, id), wenn Sie ein Objekt erhalten möchten, und wenn Sie wollen abfragen wie:

Query query = pm.newQuery(Register.class); 
query.setFilter("email== eemail"); 
query.declareParameters("string eemail"); 
return (Member)query.execute(email); 

Answer 2

PersistenceManager pm= PMF.get().getPersistenceManager(); 
Query q = pm.newQuery(Register.class); 
@SuppressWarnings("unchecked") 
List<Register> ls = (List<Register>) q.execute(); 
if(!ls.isEmpty()) 
for (Register result : ls) 
{ 
    String firstName = (String) result.getName(); 
    String email = (String) result.getEmail(); 
    String Uname = (String) result.getUName(); 
    String pass = (String) result.getPass(); 
    out.println(firstName + " "+ Uname +" "+ email + " "+pass); 
    out.println("<br/>"); 
} 

dies alle Objekte aus der Tabelle für Ihre contributio btw dank bekommen n