java - 在 J2ME 中通过 http 发送和接收数据以及处理菜单和屏幕

Question

我是 J2ME 新手，正在构建一个移动应用程序，用户可以在其中注册、登录并看到一些仅限成员(member)的屏幕，他们可以在其中执行一些操作。

(我热衷于 Web 开发，因此请纠正我使用 Web 方法的地方。此外，我清楚地了解基本的 Java 概念，但之前没有构建过移动应用程序)

到目前为止，我已经创建了第一个屏幕，其中包含一个登录表单，其中包含用户名和密码文本框以及登录和退出按钮。

我目前面临的问题是:

1. 如何同时提供注册、登录和退出的访问权限(好像手机一次只能有两个按钮)。我是否将它们作为命令按钮或普通的“出现在页面上的类似网络的按钮”提供？请告诉我如何选择任何看起来合适的选项。

2. 如何在移动应用程序中通过 http 发送和接收数据？示例代码将不胜感激。

3. 如何管理不同的屏幕？在网络开发中，我只是创建页面并将它们链接起来。在这种情况下，如何在按下注册按钮时显示注册屏幕？登录成功后的主界面？或者失败时出现错误消息？

我有不同的函数来动态生成屏幕吗？每次需要屏幕时我都会调用他们？

简单的示例将受到高度赞赏。

Answer 1

在 J2ME 中，

您拥有决定屏幕上显示内容的显示对象。有一些东西可以显示。例如表单、列表、文本框等。因此您可以创建以下显示

public class IndexScreen extends List implements CommandListener {

    //This will contain the options 
    //1. Register
    //2. Login
    //3. Exit
}


public class RegsterScreen extends Form implements CommandListener {

    //This will contain register fields and submit cancel command buttons

}

public class LoginScreen extends Form implements CommandListener {

   //This will contain Login specific controls
}

现在，一旦这些可显示对象准备就绪，您就可以继续更改某些事件的显示，例如单击命令按钮。

公共(public)无效commandAction(命令c，可显示d){

    if (c == OK) {
        nextScreen = new RegisterScreen();
        display.setCurrent(nextScreen);
    }
    if (c == BACK) {
        display.setCurrent(prevScreen);
    }

对于发送和接收数据，以下内容可能会有所帮助......

package madmin.client;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.microedition.lcdui.Display;
import madmin.res.Globals;


public class ClientRequest {

private Client client;
private Display display;
private String requestServlet;
private String requestCode;
private String requestId;
private String userId;
private String url;
private String response;
private String parameterOne;



public ClientRequest() {

}

 public boolean sendRequest() {

      boolean result = false;
      userId = Globals.getUserId();
      url = Globals.getURL() + requestServlet + "?requestCode=" + requestCode + "&requestId=" + requestId + "&userId=" + userId + "&clientIP=" + client.getIpAddress() + "&clientHostName=" + client.getHostname() + "&parameterOne=" + parameterOne;

      System.out.println("User Id value in ClientRequest " + userId);


      System.out.println("Start HTTP Connection");
      HttpConnection connection = null;
      InputStream inputstream = null;

       try {
            connection = (HttpConnection) Connector.open(url);
            connection.setRequestMethod(HttpConnection.GET);
            connection.setRequestProperty("Content-Type", "//text plain");
            connection.setRequestProperty("Connection", "close");

            System.out.println("Status Line COde: "+ connection.getResponseCode());
            System.out.println("Status Line Message: "+ connection.getResponseMessage());


            if(connection.getResponseCode()==HttpConnection.HTTP_OK){
                inputstream = connection.openInputStream();
                int length = (int) connection.getLength();
                if(length!=-1){
                    byte incomingData[] = new byte[length];
                    inputstream.read(incomingData);
                    response = new String(incomingData);
                }
                else {
                    ByteArrayOutputStream bytestream = new ByteArrayOutputStream();
                    int ch;
                    while((ch = inputstream.read())!=-1){
                        bytestream.write(ch);
                    }
                    response = new String(bytestream.toByteArray());
                    bytestream.close();
                }

               System.out.println("Response:" + response.trim());

               if(response.trim().equals("Request Submitted Successfully")){
                       result = true;
               }
               else{
                    result = false;
               }
            }
            connection.close();
            if(inputstream!=null)inputstream.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
        finally {
            if(inputstream!=null){
                try{
                    inputstream.close();
                }
                catch(Exception e){
                    e.printStackTrace();
                }
            }
        }
     return result;
 }

public Client getClient() {
    return client;
}

public void setClient(Client client) {
    this.client = client;
}

public Display getDisplay() {
    return display;
}

public void setDisplay(Display display) {
    this.display = display;
}

public String getRequestCode() {
    return requestCode;
}

public void setRequestCode(String requestCode) {
    this.requestCode = requestCode;
}

public String getRequestId() {
    return requestId;
}

public void setRequestId(String requestId) {
    this.requestId = requestId;
}

public String getRequestServlet() {
    return requestServlet;
}

public void setRequestServlet(String requestServlet) {
    this.requestServlet = requestServlet;
}

public String getResponse() {
    return response;
}

public void setResponse(String response) {
    this.response = response;
}

public String getUrl() {
    return url;
}

public void setUrl(String url) {
    this.url = url;
}

public String getUserId() {
    return userId;
}

public void setUserId(String userId) {
    this.userId = userId;
}

public String getParameterOne() {
    return parameterOne;
}

public void setParameterOne(String parameterOne) {
    this.parameterOne = parameterOne;
}

}

还有......

package madmin.client;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import madmin.res.Globals;


public class ClientResponse {

private String response;


public String getResponse(String requestId) {

         System.out.println("Start HTTP Connection");
         HttpConnection connection = null;
         InputStream inputstream = null;
         response = "";

          try{

            connection = (HttpConnection) Connector.open( Globals.getURL() + "ResponseServlet?requestId=" + requestId);
            connection.setRequestMethod(HttpConnection.GET);
            connection.setRequestProperty("Content-Type", "//text plain");
            connection.setRequestProperty("Connection", "close");

            System.out.println("Status Line COde: "+ connection.getResponseCode());
            System.out.println("Status Line Message: "+ connection.getResponseMessage());

            if(connection.getResponseCode()==HttpConnection.HTTP_OK){
                inputstream = connection.openInputStream();
                int length = (int) connection.getLength();
                if(length!=-1){
                    byte incomingData[] = new byte[length];
                    inputstream.read(incomingData);
                    response = new String(incomingData);
                }
                else {
                    ByteArrayOutputStream bytestream = new ByteArrayOutputStream();
                    int ch;
                    while((ch = inputstream.read())!=-1){
                        bytestream.write(ch);
                    }
                    response = new String(bytestream.toByteArray());
                    bytestream.close();
                }

               System.out.println("Response:" + response.trim());

              connection.close();
              if(inputstream!=null)inputstream.close();
            }
            }
            catch(Exception e){

                e.printStackTrace();
            }

    return response;
}
}

编辑: 像这样的东西

     public class MenuScreen extends List implements CommandListener{

     public MenuScreen() {
 append("Register", null);
     append("Login", null);
     append("Forgot password", null);


     select = new Command("Select", Command.OK, 1);
     addCommand(select);
     setCommandListener(this);

}

}

     public void commandAction(Command command, Displayable display) {

      if(command==List.SELECT_COMMAND){                 
        String menuItem = this.getString(menuIndex);
      }

      if(command==select){       
        if( menuItem.equals("Register"))
     display.setCurrent(new RegisterScreen())
 }
      }