一个登陆小案例演示Servlet的使用

1.servletConfig对象和servletContext对象
servlet 容器使用的 servlet 配置对象，该对象在初始化期间将信息传递给 servlet

 ServletConfig servletConfig = getServletConfig();
 //获取servlet的名字
 String servletName = servletConfig.getServletName();
 System.out.println("servletName:"+servletName);
 //获取servletcontext对象 (代表当前的web应用)
 String  username= getServletConfig().getInitParameter("username");
 System.out.println("username"+username);

//获取servlet的配置 参数的实例  代表当前的web应用 
 ServletContext servletContext = getServletContext();
 //有些数据不适合在程序中写死  这个数据是共有的    全局的
 String name = servletContext.getInitParameter("name");
 System.out.println("name:"+name);
 //拿到当前web应用可以实现数据的共享  
 servletContext.setAttribute("wdj", "hahha");
 //获取项目中的真实路径    
 String realPath = servletContext.getRealPath("aa");

下面是一个登陆的小案例：
首先配置服务器端，就是要对服务器端进行一个数据的初始化

1、在mysql中新建一个数据库
2、创建一个表，字段有id，用户名、密码
3、在表中添加用户名和密码
4、在javaee中新建一个servlet
服务器代码如下：

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");

        String name = request.getParameter("username");
        String pwd = request.getParameter("password");

        try {
            //注册驱动 
            DriverManager.registerDriver(new Driver()); //另外一种方式注册驱动可以用类的字节码，通过反射获取
            //获取连接 
            Connection connection =  DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "root", "root");
            //准备要执行的sql语句
            String sql = "select * from login where username = ? and password =?";
            //获取statement对象 执行sql语句
//          Statement statement = connection.createStatement();
            PreparedStatement statement =  connection.prepareStatement(sql);

            //设置? 占位的内容 1代表第一个?
            statement.setString(1, name);
            statement.setString(2, pwd);
            //执行sql语句
            ResultSet resultSet =  statement.executeQuery();
            //如果根据我们写sql语句查询出结果 就证明登录成功 
            //System.out.println("-------------");
            if (resultSet.next()) {
                response.getOutputStream().write("sucess".getBytes());
            }else {

                //System.out.println("登录失败");
                response.getOutputStream().write("fail".getBytes());
            }
            resultSet.close();
            statement.close();
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }   

客服端代码如下：
这里实现了get请求和post请求

package com.wdj.login;

import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

    private EditText et_name;
    private EditText et_pwd;
    private Handler handler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et_name = (EditText) findViewById(R.id.et_name);
        et_pwd = (EditText) findViewById(R.id.et_pwd);

       handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                String content = (String) msg.obj;
                Toast.makeText(getApplication(), content, 0).show();

            }
        };
    }
    //get请求
    public void click_get(View v){
        String name = et_name.getText().toString().trim();
        String pwd = et_pwd.getText().toString().trim();
        if(TextUtils.isEmpty(name) || TextUtils.isEmpty(pwd)){
            Toast.makeText(getApplication(), "用户名或密码不能为空", 0).show();
            return;
        }
        final String path = "http://192.168.80.212:8080/login/LoginServlet?username="+name+"&password="+pwd+"";
        new Thread(){
            public void run() {
                try {
                    URL url = new URL(path);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    con.setRequestMethod("GET");
                    con.setConnectTimeout(5000);
                    int code = con.getResponseCode();
                    if(code == 200){
                         InputStream inputStream = con.getInputStream();                
                         String content = UtilsToos.getInputStream(inputStream);
                         showToast(content);
                    }
                } catch (Exception e) {

                    e.printStackTrace();
                }
            };
        }.start();
    }
    //实现post请求
    public void click_post(View v){
        String name = et_name.getText().toString().trim();
        String pwd = et_pwd.getText().toString().trim();
        if(TextUtils.isEmpty(name) || TextUtils.isEmpty(pwd)){
            Toast.makeText(getApplication(), "用户名或密码不能为空", 0).show();
            return;
        }
        final String path = "http://192.168.80.212:8080/login/LoginServlet";
        //创建DefaultHttpClient对象
        final HttpClient client = new DefaultHttpClient();
        //将请求路径封装成一个HttpPost对象
        final HttpPost post = new HttpPost(path);
        //将请求要提交的参数封装成一个BasicNameValuePair对象
        BasicNameValuePair nameValuePair = new BasicNameValuePair("username", name);
        BasicNameValuePair pwdValuePair = new BasicNameValuePair("password", pwd);
        //创建一个集合，用于存放封装后的提交的数据
        final ArrayList list = new ArrayList();
        //将封装后的数据添加到集合中
        list.add(nameValuePair);
        list.add(pwdValuePair);
        new Thread(){
            public void run() {
                try {
                    //创建一个UrlEncodedFormEntity实体，指定要传输数据的编码格式
                    UrlEncodedFormEntity entity = new UrlEncodedFormEntity(list, "utf-8");
                    //设置post的请求实体
                    post.setEntity(entity);
                    //调用client的方法获取响应请求
                    HttpResponse response = client.execute(post);
                    if(response.getStatusLine().getStatusCode() == 200){
                        InputStream inputStream = response.getEntity().getContent();
                         String content = UtilsToos.getInputStream(inputStream);
                         //showToast(content);           //用runOnuiThread实现ui的更新
                         Message msg = Message.obtain();
                         msg.obj = content;
                         handler.sendMessage(msg);      //用handler发送消息机制更新ui

                    }
                } catch (Exception e) {

                    e.printStackTrace();
                }
            };
        }.start();
    }
    public void showToast(final String content){
        runOnUiThread(new Runnable(){

            @Override
            public void run() {
                Toast.makeText(getApplication(), content, 0).show();
            }

        });
    }
}

用到的工具类：

package com.heima.login;

import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

public class UtilsToos {

    public static String getInputStream(InputStream in) throws Exception {
        ByteArrayOutputStream boas = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int len;
    while((len = in.read(buffer)) != -1){
        boas.write(buffer, 0, len);
    }
        String str = boas.toString();
        return str;
    }

}