如何获取数据库表数据（oracle 11g）作为 Json 对象并在 Android 中显示该 Json 对象？

Question

我正在尝试在 android 应用程序和 oracle DB 之间建立连接。我发现我必须创建一个 Web 服务，所以我开始编写一个 servlet，它将创建与数据库的连接并将数据作为 JSON 对象返回，该对象可以在 android 上解析。
首先我写了一个 servlet 来返回 HTML 格式的数据，这很简单，下面是我的 servlet 代码

package a.b.c;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletDatabaseConnect extends HttpServlet  
{
    protected void doPost(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException
    {
        PrintWriter pw=res.getWriter();
        res.setContentType("text/html");        
        String tb=req.getParameter("table");    

        try
        {
             Class.forName("oracle.jdbc.driver.OracleDriver");
             Connection con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE","system","admin");
             Statement st=con.createStatement();
             System.out.println("connection established successfully...!!");     

             ResultSet rs=st.executeQuery("Select * from "+tb);

             pw.println("<table border=1>");
                 while(rs.next())
                 {
                     pw.println("<tr><td>"+rs.getInt(1)+"</td><td>"+rs.getString(2)+"</td>"+
                                      "<td>"+rs.getString(3)+"</td></tr>");
                 }
             pw.println("</table>");
             pw.close();
        }
        catch (Exception e){
            e.printStackTrace();
        }

    }
}

如何修改我的 servlet 代码以返回 JSON 对象格式的数据？

Answer 1

你必须使用Jackson将你的信息转换成json格式，这个动作叫做序列化，Jackson是完成这个任务的完美工具，你可以看一些例子here

Answer 2

在这里我找到了我自己的答案，我使用了 JSON-simple-1.1.jar，它可以在 java2s.com 上免费获得

following is my servlet code now

package servlet.package1;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.logging.Level;
import java.util.logging.Logger;

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

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;




@WebServlet("/ServletTalk")
public class ServletTalk extends HttpServlet {
    private static final long serialVersionUID = 1L;


    public ServletTalk() {
        super();
        // TODO Auto-generated constructor stub


    }

 // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //response.setContentType("text/html;charset=UTF-8");
        JSONObject json = new JSONObject();


        //ObjectOutputStream out = new ObjectOutputStream(response.getOutputStream());
        Enumeration paramNames = request.getParameterNames();

        String[] params = new String[2];
        int i = 0;
        while (paramNames.hasMoreElements()) {
            String paramName = (String) paramNames.nextElement();


            //System.out.println(paramName);
            String[] paramValues = request.getParameterValues(paramName);
            params[i] = paramValues[0];

            //System.out.println(params[i]);
            i++;

        }

        String sql = "SELECT LOGIN_ID, PASSWORD FROM SE_USER where LOGIN_ID=? and PASSWORD=?";
        Connection con = getConnection();

        try {
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setString(1, params[0]);
            ps.setString(2, params[1]);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                json.put("info", "success");
                /*String sql1 = "SELECT uname, password FROM users";
                PreparedStatement ps2=con.prepareStatement(sql1);
                ResultSet rs2=ps2.executeQuery();
                JSONArray arrayJSON=new JSONArray();
                while(rs2.next())
                {
                    JSONObject arrayObject = new JSONObject();
                    arrayObject.put("userName", rs2.getString("uname"));
                    arrayObject.put("passWord", rs2.getString("password"));
                    arrayJSON.add(arrayObject);
                }


                json.put("IDS",arrayJSON);*/
            } else {
                json.put("info", "fail");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        //System.out.println(json);
        response.setContentType("application/json");
        response.setCharacterEncoding("UTF-8");
        //json.put("info", disp);
        response.getWriter().write(json.toString());
    }

    /** 
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

    public static Connection getConnection() {
    Connection con = null;
    try {
        Class.forName("com.mysql.jdbc.Driver");//Mysql Connection
        //Class.forName("oracle.jdbc.driver.OracleDriver");//Oracle Connection
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(ServletTalk.class.getName()).log(Level.SEVERE, null, ex);
    }
    try {
        con = DriverManager.getConnection("jdbc:mysql://localhost:8889/a9613246_mydata1", "root", "root");//mysql database
        //con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "hemabh_demo", "hemabh_demo");//oracle database

    } catch (SQLException ex) {
        Logger.getLogger(ServletTalk.class.getName()).log(Level.SEVERE, null, ex);
    }
    return con;
}



}

返回的 JSON 格式不正确，但无需任何外部库（如 Gson 等）即可轻松解析。

找到答案很有趣...谢谢