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从servlet生成JSON(Generating JSON from servlet)

 在我的Android应用程序中，我使用以下代码复制特定表中的整个数据。 但是当我检查servlet输出时，似乎生成了重复的值。 您可以通过运行以下代码来验证这一点。 我不知道为什么会这样。 我需要将值从servlet传递给我的应用程序作为JSON对象..  
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.json.JSONObject;

public class vlgmas extends HttpServlet {

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    try {
        // TODO output your page here
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet vlgmas</title>");  
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet vlgmas at " + request.getContextPath () + "</h1>");
        out.println("</body>");
        out.println("</html>");

    } finally {            
        out.close();
    }
}


@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
     try {

        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet Pickvalue</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet Pick at " + request.getContextPath () + "</h1>");
        doPost(request,response);
        out.println("</body>");
        out.println("</html>");

    } finally
    {
        out.close();
    }
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    //processRequest(request, response);
    String vname = null,vcode=null,divsec=null;
    JSONObject obj = new JSONObject();
    List list = new ArrayList();
    JSONObject obj2 = new JSONObject();
    PrintWriter out = response.getWriter();
    String vn[]=new String[2000],vc[]=new String[2000],ds[]=new String[2000];
    int t,r1=0,r2=0,r3=0;
    try
    {
        Class.forName("oracle.jdbc.driver.OracleDriver");
    java.sql.Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.1.200:1521:pdsm", "test", "test");
    Statement stmt=conn.createStatement();

        {
        ResultSet rs = stmt.executeQuery("select * from cn_vlgmas");
        while(rs.next())
        {
            //vn[r1++]=rs.getString ("vlgname");
            //vc[r2++]=rs.getString("vlgcode");
            //ds[r3++]=rs.getString("divsec");
            vname=rs.getString ("vlgname");
            vcode=rs.getString("vlgcode");
            divsec=rs.getString("divsec");
            obj.put("vname",vname);
            obj.put("vcode",vcode);
            obj.put("divsec",divsec);
            list.add(obj);
            obj2.accumulate("get", list);
            out.println(obj2);
        }
       /*for(t=0;t<r1;t++)
           {
            //out.println(vn[t]+","+vc[t]+","+ds[t]+" ");
            obj.put("vname",vn[t]);
            obj.put("vcode",vc[t]);
            obj.put("divsec",ds[t]);
            list.add(obj);
            //obj.append("rec", obj);
            //out.println(list);
            //obj.accumulate("get", list);
            //out.println(obj);
            obj2.accumulate("get", obj);
            //out.println(obj2);
            }*/


        }

    }catch(Exception e)
    {
        out.println("error"+e.toString());
    }
}


@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>
}
 
 任何人都可以帮助我。 

in my android application I'm using the following code to copy the entire data in a particular table. But It seems to be generate duplicate values when I check with servlet output. You can verify this by running the following code. I don't know why this happened. I need to pass the values from servlet to my application as JSON Object..  
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.json.JSONObject;

public class vlgmas extends HttpServlet {

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    try {
        // TODO output your page here
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet vlgmas</title>");  
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet vlgmas at " + request.getContextPath () + "</h1>");
        out.println("</body>");
        out.println("</html>");

    } finally {            
        out.close();
    }
}


@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
     try {

        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet Pickvalue</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet Pick at " + request.getContextPath () + "</h1>");
        doPost(request,response);
        out.println("</body>");
        out.println("</html>");

    } finally
    {
        out.close();
    }
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    //processRequest(request, response);
    String vname = null,vcode=null,divsec=null;
    JSONObject obj = new JSONObject();
    List list = new ArrayList();
    JSONObject obj2 = new JSONObject();
    PrintWriter out = response.getWriter();
    String vn[]=new String[2000],vc[]=new String[2000],ds[]=new String[2000];
    int t,r1=0,r2=0,r3=0;
    try
    {
        Class.forName("oracle.jdbc.driver.OracleDriver");
    java.sql.Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.1.200:1521:pdsm", "test", "test");
    Statement stmt=conn.createStatement();

        {
        ResultSet rs = stmt.executeQuery("select * from cn_vlgmas");
        while(rs.next())
        {
            //vn[r1++]=rs.getString ("vlgname");
            //vc[r2++]=rs.getString("vlgcode");
            //ds[r3++]=rs.getString("divsec");
            vname=rs.getString ("vlgname");
            vcode=rs.getString("vlgcode");
            divsec=rs.getString("divsec");
            obj.put("vname",vname);
            obj.put("vcode",vcode);
            obj.put("divsec",divsec);
            list.add(obj);
            obj2.accumulate("get", list);
            out.println(obj2);
        }
       /*for(t=0;t<r1;t++)
           {
            //out.println(vn[t]+","+vc[t]+","+ds[t]+" ");
            obj.put("vname",vn[t]);
            obj.put("vcode",vc[t]);
            obj.put("divsec",ds[t]);
            list.add(obj);
            //obj.append("rec", obj);
            //out.println(list);
            //obj.accumulate("get", list);
            //out.println(obj);
            obj2.accumulate("get", obj);
            //out.println(obj2);
            }*/


        }

    }catch(Exception e)
    {
        out.println("error"+e.toString());
    }
}


@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>
}
 
Can anyone help me please.

原文：https://stackoverflow.com/questions/14621600

更新时间：2022-11-17 08:11

最满意答案

 至少ndb数据存储区缓存包括memcache ：  
 您观察到的模式可以在本节中解释：  
 
  Memcache不支持事务。 因此，旨在应用于数据存储和内存缓存的更新可能只对两者中的一个进行。 为了在这种情况下保持一致性（可能以性能为代价），更新的实体将从内存缓存中删除，然后写入数据存储区。  

At least the ndb datastore caches include memcache: 
The pattern you observed could be explained in this section: 
 
 Memcache does not support transactions. Thus, an update meant to be applied to both the Datastore and memcache might be made to only one of the two. To maintain consistency in such cases (possibly at the expense of performance), the updated entity is deleted from memcache and then written to the Datastore.

从servlet生成JSON(Generating JSON from servlet)

最满意答案

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