Connecting to databases like Mysql, SQL Server or Oracle on J2ME devices -优快云博客

本文介绍了一种在受限的CLDC环境下通过MIDlets调用Servlet实现与数据库连接的方法，并提供了一个具体的Java代码示例，展示了如何从J2ME设备传递数据库名、用户名和密码到服务器端。

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CLDC framework, do not support JDBC APIS. To connect to databases from devices that have CLDC configuration, you can call a Servlet from MIDLets. Connection to database, running the queries and other functionalities need to be implemented in the Servlet. Passing the parameters to servlet like username, password can be done from MIDLets.

The example below takes database name, username and password from MIDlet running on the J2ME device and passes it to the Servlet. The status of connection is passed to MIDlet:

import java.io.*;
import java.util.*;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;

public class testMySQL extends MIDlet implements CommandListener {
    private String username;
    private String url = 
        "http://localhost:8080/servlets-examples/servlet/getConnection";
    
    private Display display;
    private Command exit = new Command("EXIT", Command.EXIT, 1);;
    private Command connect = new Command("Connect", Command.SCREEN, 1);
    private TextField tb;
    private Form menu;
    private TextField tb1;
    private TextField tb2;
    DB db;
    
    public testMySQL() throws Exception {
        display = Display.getDisplay(this);
        
    }
    
    public void startApp() {
        displayMenu();
    }
    
    public void displayMenu() {
        menu = new Form("Connect");
        
        tb = new TextField("Please input database: ","",30,
                TextField.ANY );
        
        tb1 = new TextField("Please input username: ","",30,
                TextField.ANY);
        
        tb2 = new TextField("Please input password: ","",30,
                TextField.PASSWORD);
        
        menu.append(tb);
        menu.append(tb1);
        menu.append(tb2);
        menu.addCommand(exit);
        menu.addCommand(connect);
        menu.setCommandListener(this);
        display.setCurrent(menu);
    }
    
    public void pauseApp() {}
    
    public void destroyApp(boolean unconditional) {}
    
    public void commandAction(Command command, Displayable screen) {
        if (command == exit) {
            destroyApp(false);
            notifyDestroyed();
        } else if (command == connect) {
            db  = new DB(this);
            db.start();
            db.connectDb(tb.getString(),tb1.getString(),tb2.getString());
        }
    }
    
    public class DB implements Runnable {
        testMySQL midlet;
        private Display display;
        String db;
        String user;
        String pwd;
        public DB(testMySQL midlet) {
            this.midlet = midlet;
            display = Display.getDisplay(midlet);
        }
        
        public void start() {
            Thread t = new Thread(this);
            t.start();
        }
        
        public void run() {
            StringBuffer sb = new StringBuffer();
            try {
                HttpConnection c = (HttpConnection) Connector.open(url);
                c.setRequestProperty(
                   "User-Agent","Profile/MIDP-1.0, Configuration/CLDC-1.0");
                c.setRequestProperty("Content-Language","en-US");
                c.setRequestMethod(HttpConnection.POST);
                
                DataOutputStream os = 
                        (DataOutputStream)c.openDataOutputStream();
                
                os.writeUTF(db.trim());
                os.writeUTF(user.trim());
                os.writeUTF(pwd.trim());
                os.flush();
                os.close();
                
                // Get the response from the servlet page.
                DataInputStream is =(DataInputStream)c.openDataInputStream();
                //is = c.openInputStream();
                int ch;
                sb = new StringBuffer();
                while ((ch = is.read()) != -1) {
                    sb.append((char)ch);
                }
                showAlert(sb.toString());
                is.close();
                c.close();
            } catch (Exception e) {
                showAlert(e.getMessage());
            }
        }
            /* This method takes input from user like db,user and pwd and pass
            to servlet */
        public void connectDb(String db,String user,String pwd) {
            this.db = db;
            this.user = user;
            this.pwd = pwd;
        }
        
        /* Display Error On screen*/
        private void showAlert(String err) {
            Alert a = new Alert("");
            a.setString(err);
            a.setTimeout(Alert.FOREVER);
            display.setCurrent(a);
        }
        
    };
}

import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class getConnection extends HttpServlet {
    
    public void init() {
    }
    
    public void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, 
            IOException {
        
        DataInputStream in = new DataInputStream(
                (InputStream)request.getInputStream());
        
        String db = in.readUTF();
        String user = in.readUTF();
        String pwd = in.readUTF();
        
        String message ="jdbc:mysql://localhost:3306/"+db+","+user+","+pwd;
        try {
            
            connect(db.toLowerCase().trim(),user.toLowerCase().trim(), 
                    pwd.toLowerCase().trim());
            
            message += "100 ok";
            
        } catch (Throwable t) {
            message += "200 " + t.toString();
        }
        response.setContentType("text/plain");
        response.setContentLength(message.length());
        PrintWriter out = response.getWriter();
        out.println(message);
        in.close();
        out.close();
        out.flush();
    }
    
    public void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, 
            IOException {
        
        doPost(request,response);
    }
    
    /* This method connects to MYSQL database*/
    private void connect(String db, String user,String pwd) 
    throws Exception {
        
        // Establish a JDBC connection to the MYSQL database server.
        //Class.forName("org.gjt.mm.mysql.Driver");
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        Connection conn = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/"+db,user,pwd);
        
        // Establish a JDBC connection to the Oracle database server.
        //DriverManager.registerDriver(new oracle.jdbc.OracleDriver());
        //Connection conn = DriverManager.getConnection(
        //      "jdbc:oracle:thin:@localhost:1521:"+db,user,pwd);
        
        // Establish a JDBC connection to the SQL database server.
        //Class.forName("net.sourceforge.jtds.jdbc.Driver");
        //Connection conn = DriverManager.getConnection(
        //      "jdbc:jtds:sqlserver://localhost:1433/"+db,user,pwd);
    }
}