Web-Servlet-2

发表于

Request 接收表单参数

Request功能很多, 其主要作用就是处理浏览器请求. 用户通过表单提交的参数可以通过Request对象提供的API方法读取

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String name = request.getParamter("name");

案例:

  1. 编写表单 webapp/login.html

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    <!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>登录表单</title>
    </head>
    <body>
        <h1>登录</h1>
        <p>使用request对象接收表单参数</p>
        <!-- 向 login url发起post请求 -->
        <form action="login" method="post">
            <div>
                <label>用户</label>
                <input type="text" name="user"> 
            </div>
            <div>
                <label>密码</label>
                <input type="password" name="pwd"> 
            </div>
            <input type="submit" value="登录">   
        </form>
    </body>
    </html>

  2. 测试显示表单

  3. 编写Servlet

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    public class LoginServlet extends HttpServlet {
         private static final long serialVersionUID = 1L;
         protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
             //利用request的API获取表单参数
             String name = request.getParameter("user");
             String pwd = request.getParameter("pwd");
             System.out.println(name+","+pwd);
     
             response.setContentType("text/html; charset=utf-8"); 
             PrintWriter out=response.getWriter();
             out.print("OK"); 
         }
     }

参数编码问题

  1. 网络和IO 每次只能传输一个字节(8位)信息!
  2. 字符是16位无符号整数
  3. 利用网络传输字符时候, 需要将字符进行拆分才能传输
  4. 字符的拆分方案称为字符的编码!

Post请求时候, 在获取请求参数之前设置请求的编码可以解决编码问题.
案例:

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public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    protected void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException, IOException {
        //在读取参数之前设置request的编码,处理解码问题
        request.setCharacterEncoding("UTF-8");
        //利用request的API获取表单参数
        String name = request.getParameter("user");
        String pwd = request.getParameter("pwd");
        System.out.println(name+","+pwd);
        response.setContentType("text/html; charset=utf-8"); 
        PrintWriter out=response.getWriter();
        out.print("OK"); 
    }
}

接收get请求参数

getParamter不仅可以接受post请求参数, 也可以接收get请求参数.
get编码问题可以在Tomcat配置文件server.xml中配置:

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<Connector URIEncoding="UTF-8" connectionTimeout="20000" port="8080" protocol="HTTP/1.1" redirectPort="8443"/>

案例:

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public class GetDemoServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //接收浏览器通过 get 请求发送的参数
        //如果浏览器没有提供对应的参数, 则接收到null
        String id=request.getParameter("id");
        String name=request.getParameter("name");
        System.out.println(id+", "+name);
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.print("OK");
    }
}

配置:

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<servlet>
  <description></description>
  <display-name>GetDemoServlet</display-name>
  <servlet-name>GetDemoServlet</servlet-name>
  <servlet-class>day03.GetDemoServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>GetDemoServlet</servlet-name>
  <url-pattern>/get-demo</url-pattern>
</servlet-mapping>

利用Servlet将数据库中的表显示到浏览器中

1. 创建表

创建员工表:

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create database web;
use web;
create table t_emp(
    empno int auto_increment primary key,
    ename varchar(100),
    mgr int,
    deptno int,
    hiredate datetime,
    salary double,
    comm double
);
insert into t_emp (empno, ename, mgr, deptno, hiredate, salary, comm)
values (null, 'Tom', 0, null, now(), 1000, 200);

insert into t_emp (empno, ename, mgr, deptno, hiredate, salary, comm)
values (null, 'Jerry', 1, null, now(), 2000, 100);

2. 编写数据库连接配置文件 db.properties

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driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/web?characterEncoding=utf8&useUnicode=true&useSSL=false
username=root
password=

3. 编写数据库连接工具

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public class DBUtil {
    private static String driver;
    private static String url;
    private static String username;
    private static String password;
    static {
        try {
            InputStream in = DBUtil.class.getClassLoader().getResourceAsStream("db.properties");
            Properties cfg = new Properties();
            cfg.load(in);
            in.close();
            driver = cfg.getProperty("driver");
            url = cfg.getProperty("url");
            username=cfg.getProperty("username");
            password=cfg.getProperty("password");
        }catch(Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    public static Connection getConnection() throws Exception{
        Class.forName(driver);
        Connection conn = DriverManager.getConnection(url,username,password);
        return conn;
    }

    public static void close(Connection conn) {
        try {
            if(conn!=null) {
                conn.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

4. 利用JUnit进行测试:

  1. 导入JUnit

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    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
    </dependency>

  2. 编写测试案例:

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    public class TestCase {
        @Test
        public void test() {
            System.out.println("Hello World!"); 
        }

        @Test
        public void testHello() {
            System.out.println("Hello Kitty!"); 
        }

        @Test
        public void testGetConnection() {
            String sql = "select now() d";
            Connection conn = null;
            try {
                conn = DBUtil.getConnection();
                Statement st = conn.createStatement();
                ResultSet rs = st.executeQuery(sql);
                while(rs.next()) {
                    Date date=rs.getDate("d");
                    System.out.println(date);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }finally{
                DBUtil.close(conn);
            }
        }
    }

5. 编写Servlet 显示表内容

代码:

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public class ListServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获得out对象
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<meta charset=\"UTF-8\">");
        out.println("<title>登录表单</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>员工列表</h1>"); 

        String sql="select empno, ename, mgr, hiredate, deptno, salary, comm from t_emp";
        Connection conn = null;
        try {
            conn = DBUtil.getConnection();
            Statement st = conn.createStatement();
            ResultSet rs = st.executeQuery(sql);
            //输出表格头
            out.println("<table>");
            out.println("<tr>");
            out.println("<td>编号</td>");
            out.println("<td>姓名</td>");
            out.println("<td>入职日期</td>");
            out.println("</tr>");
            while(rs.next()) {
                int empno = rs.getInt("empno");
                String ename = rs.getString("ename");
                Date date = rs.getDate("hiredate");
                //System.out.println(empno+","+ename);
                out.println("<tr>");
                out.println("<td>"+empno+"</td>");
                out.println("<td>"+ename+"</td>");
                out.println("<td>"+date+"</td>");
                out.println("</tr>");
            }
            out.println("</table>");
        }catch (Exception e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn);
        }
        out.println("</body>");
        out.println("</html>"); 
    }
}

配置:

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<servlet>
  <description></description>
  <display-name>ListServlet</display-name>
  <servlet-name>ListServlet</servlet-name>
  <servlet-class>day03.ListServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>ListServlet</servlet-name>
  <url-pattern>/list</url-pattern>
</servlet-mapping>

测试:

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http://localhost:8080/Servlet03/list