java servlet数据库查询并将数据显示到jsp页面

• 需要的jar包：mysql-connector-java.jar
• build path只是个jar包的引用，部署的时候想不丢包最好还是手动拷贝到对应项目的lib文件下。
• 在try{}中定义的变量为局部变量。
• WEB-INF对于浏览器是无法直接通过url访问的，因此要想跳转到WEB-INF目录下必须采用服务端的foward方法而不能采用redirect方法。
• 注意网页的编码问题，一般全采用utf-8就没乱码了。
• 注意pageContext,request,session,application对象的scope，作用范围。

目录结构为：

首先我们创建实体类：Student

package micro.entity;

public class Student {
    String name;
    int no;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getNo() {
        return no;
    }
    public void setNo(int no) {
        this.no = no;
    }

}

• 创建dao，负责数据库的连接与关闭：

• package micro.dao;
  
  import java.sql.Connection;
  import java.sql.DriverManager;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import com.mysql.jdbc.PreparedStatement;
  
  public class Dao {
      public static Connection getConnection() throws SQLException
      {
          String url = "jdbc:mysql://localhost:3306/micro";
          String username = "root";
          String password = "root";
          Connection conn = null;
          try
          {
              Class.forName("com.mysql.jdbc.Driver");
              conn = DriverManager.getConnection(url, username, password);
          }
          catch(ClassNotFoundException e)
          {
              e.printStackTrace();
          }
          return conn;
      }
      public static void close(ResultSet rs,PreparedStatement ps,Connection conn) throws SQLException
      {
          try
          {
              rs.close();
              ps.close();
              conn.close();
          }
          catch(SQLException e)
          {
              e.printStackTrace();
          }
      }
  }

  • 创建查询方法类（按名字查询和按学号查询）：

  • package micro.dao;
    
    import java.sql.Connection;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import micro.entity.Student;
    
    import com.mysql.jdbc.PreparedStatement;
    
    public class SearchDao {
        /**
         * @param micro
         * @return
         * @throws SQLException
         */
        // static String sql = "select * from Student where ? = ?";
        public static int getIdByName(String name) throws SQLException {
            int id = -1;
            try {
                Connection conn = Dao.getConnection();
                PreparedStatement ps = (PreparedStatement) conn
                        .prepareStatement("select * from Student where name = ?");
                // ps.setString(1, "name");
                ps.setString(1, name);
                ResultSet rs = ps.executeQuery();
                // List<Student> list = new ArrayList();
                while (rs.next()) {
                    id = rs.getInt("id");
                }
                Dao.close(rs, ps, conn);
    
            } catch (SQLException e) {
                e.printStackTrace();
            }
    
            return id;
        }
    
        /**
         * @param id
         * @return
         * @throws SQLException
         */
        public static String getNameById(int id) throws SQLException {
            Connection conn;
            String name = null;
            try {
                conn = Dao.getConnection();
                PreparedStatement ps = (PreparedStatement) conn
                        .prepareStatement("select * from Student where id = ?");
                // ps.setString(1, "");
                ps.setInt(1, id);
                ResultSet rs = ps.executeQuery();
                while (rs.next()) {
                    name = rs.getString("name");
                }
                Dao.close(rs, ps, conn);
    
            } catch (SQLException e) {
                e.printStackTrace();
            }
            return name;
        }
    }

    • 需要执行业务的servlet:

    • package micro.search;
      
      import java.io.IOException;
      import java.sql.SQLException;
      
      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 micro.dao.SearchDao;
      
      /**
       * Servlet implementation class FindName
       */
      @WebServlet("/FindName")
      public class FindNameOrNo extends HttpServlet {
          private static final long serialVersionUID = 1L;
      
          /**
           * @see HttpServlet#HttpServlet()
           */
          public FindNameOrNo() {
              super();
              // TODO Auto-generated constructor stub
          }
      
          /**
           * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
           */
          protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
              // TODO Auto-generated method stub
              this.doPost(request, response);
          }
      
          /**
           * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
           */
          protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
              // TODO Auto-generated method stub
              String username = request.getParameter("username");
              int id = Integer.valueOf(request.getParameter("id"));
      
              if(!username.equals(""))
              {
                  try
                  {
                      int no = SearchDao.getIdByName(username);
                      request.setAttribute("id", no);
                  }
                  catch(SQLException e)
                  {
                      System.out.println("数据库出现异常");
                      e.printStackTrace();
                  }
                  request.getRequestDispatcher("/WEB-INF/IdResult.jsp").forward(request, response);
              }
              else
              {
                  try
                  {
                      String name = SearchDao.getNameById(id);
                      request.setAttribute("name", name);
                  }
                  catch(SQLException e)
                  {
                      System.out.println("数据库出现异常");
                      e.printStackTrace();
                  }
                  request.getRequestDispatcher("/WEB-INF/NameResult.jsp").forward(request, response);
              }
              }
      
      }

      • welcome.jsp页面：

      • <%@ page language="java" contentType="text/html; charset=utf-8"
            pageEncoding="utf-8"%>
        <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
        <html>
        <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
        <title>Insert title here</title>
        </head>
        <body>
            <form action="myQuery" method="post">
                请输入学生姓名：<input type="text" name="username" /> <br /> 请输入学生学号：<input
                    type="text" name="id" /> <br /> <input type="submit" value="查询" />
            </form>
        </body>
        </html>

        • 返回学号的页面：

        • <%@ page language="java" contentType="text/html; charset=utf-8"
              pageEncoding="utf-8"%>
          <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
          <html>
          <head>
          <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
          <title>Insert title here</title>
          </head>
          <body>
          <h1>
          查询结果对应的学号为:<%= request.getAttribute("id") %>
          </h1>
          <form action="welcome.jsp" method = "post" >
          <input type = "submit" value = "返回" />
          </form>
          </body>
          </html>

          • 返回名字的页面：

          • <%@ page language="java" contentType="text/html; charset=utf-8"
                pageEncoding="utf-8"%>
            <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
            <html>
            <head>
            <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
            <title>Insert title here</title>
            </head>
            <body>
                <h1>
                    该学号的同学名字为：<%=request.getAttribute("name")%>
                </h1>
                <form action="welcome.jsp" method="post">
                    <input type="submit" value="返回" />
                </form>
            </body>
            </html>

            • web.xml：

            • <?xml version="1.0" encoding="UTF-8"?>
              <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
                  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
                  version="2.5">
                  <servlet>
                      <servlet-name>Query</servlet-name>
                      <servlet-class>micro.search.FindNameOrNo</servlet-class>
                  </servlet>
                  <servlet-mapping>
                      <servlet-name>Query</servlet-name>
                      <url-pattern>/myQuery</url-pattern>
                  </servlet-mapping>
                  <welcome-file-list>
                      <welcome-file>welcome.jsp</welcome-file>
                  </welcome-file-list>
              </web-app>