Android客户端post方式连接web（servlet）服务器实现简单登录

注意点：

1、访问网络的工作不能在主线程（UI）中进行，如果耗时过程则会导致程序出错 ------（子线程中进行）

2、子线程不能更新UI -------（主线程中进行）

3、使用Handler配合子线程更新主线程时要注意内存泄露的问题，解决内存泄露的方法之一就是以弱引用的形式：

//弱引用，防止内存泄露
    private static class MyHandler extends Handler {
        private final WeakReference mActivity;

        public MyHandler(MainActivity activity) {
            mActivity = new WeakReference(activity);
        }

        @Override
        public void handleMessage(Message msg) {
            System.out.println(msg);
            if (mActivity.get() == null) {
                return;
            }
            mActivity.get().updateUIThread(msg);
        }
    }

4、在使用post向服务器发送请求时，要注意发送数据参数的格式，发送的参数是以key=value&key=value&key=value的格式进行发送的，value一般都要进行URL编码

//我们请求的数据
            String data = "password="+ URLEncoder.encode(passwd,"UTF-8")+
                    "&username="+URLEncoder.encode(username,"UTF-8");

5、使用模拟器进行测试时，URL中的IP地址不是127.0.0.1，而是10.0.2.2

private static String LOGIN_URL = "http://10.0.2.2:8080/webtest/loginaction";

实例：在Android客户端中输入用户名和密码之后，将其提交至服务器，服务器进行判断用户名和密码是否正确，如果正确则返回success，失败则返回fail

配置服务器

在搭建好tomcat服务器之后，在eclipse中创建servlet文件

LoginAction.java（服务器）

package Login;

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.HashMap;

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

import java.util.HashMap;
import java.util.Map;

/**
 * Servlet implementation class LoginAction
 */
@WebServlet("/LoginAction")
public class LoginAction extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginAction() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
		
		//设置客户端的解码方式为utf-8
		response.setContentType("text/html;charset=utf-8");
		//
		response.setCharacterEncoding("UTF-8");
		
		PrintWriter out = response.getWriter();
		
		String result = "";
		
		String name = request.getParameter("username");
		String pwd = request.getParameter("password");
		
		//System.out.println("name="+name);
		//System.out.println("password="+pwd);
		if (name.equals("admin")&&pwd.equals("123")) {
			result = "success";
		}
		else{
			result = "fail";
		}
		out.write(result);
		out.flush();
		out.close();
		System.out.println(result);
		
		
	}

}

在eclipse中中配置web.xm文件，该文件一般在WebContent ---> WEB-INF的文件夹下

在web.xml文件中添加如下代码：

   
        LoginAction  
        Login.LoginAction  
    
      
        LoginAction  
        /loginaction  
     

Android客户端

MainActivity.java

package com.example.administrator.httpconnectlogin;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.lang.ref.WeakReference;


public class MainActivity extends AppCompatActivity {

    private Button button;
    private EditText edit1,edit2;
    private MyHandler myhandler = new MyHandler(this);
    public static final String TAG="MainActivity";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        InitView();
    }

    //弱引用，防止内存泄露
    private static class MyHandler extends Handler {
        private final WeakReference mActivity;

        public MyHandler(MainActivity activity) {
            mActivity = new WeakReference(activity);
        }

        @Override
        public void handleMessage(Message msg) {
            System.out.println(msg);
            if (mActivity.get() == null) {
                return;
            }
            mActivity.get().updateUIThread(msg);
        }
    }

    //配合子线程更新UI线程
    private void updateUIThread(Message msg){
        Bundle bundle = new Bundle();
        bundle = msg.getData();
        String result = bundle.getString("result");
        Toast.makeText(MainActivity.this, result, Toast.LENGTH_SHORT).show();
    }
    void InitView(){
        button = (Button) findViewById(R.id.btn);
        edit1 = (EditText) findViewById(R.id.editText1);
        edit2 = (EditText) findViewById(R.id.editText2);
       // Toast.makeText(MainActivity.this, "str111", Toast.LENGTH_SHORT).show();
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if (edit1.toString().isEmpty()||edit2.toString().isEmpty()) {
                    Toast.makeText(MainActivity.this, "学号或密码不能为空", Toast.LENGTH_SHORT).show();
                }
                else{
                    //开启访问数据库线程
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            String str = HttpLogin.LoginByPost(edit1.getText().toString(),edit2.getText().toString());
                            Bundle bundle = new Bundle();
                            bundle.putString("result",str);
                            Message msg = new Message();
                            msg.setData(bundle);
                            myhandler.sendMessage(msg);
                        }
                    }).start();
                }

            }
        });
    }

}

连接服务器的自定义工具类

HttpLogin.java

package com.example.administrator.httpconnectlogin;

import android.util.Log;

import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by Administrator on 2016/10/5.
 */
public class HttpLogin {
    private static String LOGIN_URL = "http://10.0.2.2:8080/webtest/loginaction";

    public static String LoginByPost(String username,String passwd){
        Log.d(MainActivity.TAG,"启动登录线程");
        String msg = "";
        try {
            //初始化URL
            URL url = new URL(LOGIN_URL);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            Log.d(MainActivity.TAG,"11111");
            //设置请求方式
            conn.setRequestMethod("POST");

            //设置超时信息
            conn.setReadTimeout(5000);
            conn.setConnectTimeout(5000);

            //设置允许输入
            conn.setDoInput(true);
            //设置允许输出
            conn.setDoOutput(true);

            //post方式不能设置缓存，需手动设置为false
            conn.setUseCaches(false);

            //我们请求的数据
            String data = "password="+ URLEncoder.encode(passwd,"UTF-8")+
                    "&username="+URLEncoder.encode(username,"UTF-8");

            //獲取輸出流
            OutputStream out = conn.getOutputStream();

            out.write(data.getBytes());
            out.flush();
            out.close();
            conn.connect();

            if (conn.getResponseCode() == 200) {
                // 获取响应的输入流对象
                InputStream is = conn.getInputStream();
                // 创建字节输出流对象
                ByteArrayOutputStream message = new ByteArrayOutputStream();
                // 定义读取的长度
                int len = 0;
                // 定义缓冲区
                byte buffer[] = new byte[1024];
                // 按照缓冲区的大小，循环读取
                while ((len = is.read(buffer)) != -1) {
                    // 根据读取的长度写入到os对象中
                    message.write(buffer, 0, len);
                }
                // 释放资源
                is.close();
                message.close();
                // 返回字符串
                msg = new String(message.toByteArray());

                return msg;
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        Log.d(MainActivity.TAG,"exit");
        return msg;
    }
}

在AndroidManifest文件中添加访问网络权限