本教程假设您已了解JDBC应用程序的工作原理.在通过servlet开始数据库访问之前,请确保您具有正确的JDBC环境设置以及数据库.
有关如何使用JDBC及其环境设置访问数据库的更多详细信息,您可以去通过我们的 JDBC教程.
从基本概念入手,让我们创建一个简单的表,并在该表中创建少量记录,如下所示;
创建员工 TEST数据库中的表,使用以下步骤 :
打开命令提示符并更改安装目录如下 :
C:\> C:\>cd Program Files\MySQL\bin C:\Program Files\MySQL\bin>
按如下方式登录数据库
C:\Program Files\MySQL\bin>mysql -u root -p Enter password: ******** mysql>
在 TEST 中创建表员工>数据库如下 :
mysql> use TEST; mysql> create table Employees ( id int not null, age int not null, first varchar (255), last varchar (255) ); Query OK, 0 rows affected (0.08 sec) mysql>
最后,您在Employee表中创建几条记录,如下所示 :
mysql> INSERT INTO Employees VALUES (100, 18, 'Zara', 'Ali'); Query OK, 1 row affected (0.05 sec) mysql> INSERT INTO Employees VALUES (101, 25, 'Mahnaz', 'Fatma'); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO Employees VALUES (102, 30, 'Zaid', 'Khan'); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO Employees VALUES (103, 28, 'Sumit', 'Mittal'); Query OK, 1 row affected (0.00 sec) mysql>
这是一个示例,说明如何使用Servlet访问TEST数据库.
// Loading required libraries import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; import java.sql.*; public class DatabaseAccess extends HttpServlet{ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // JDBC driver name and database URL static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; static final String DB_URL="jdbc:mysql://localhost/TEST"; // Database credentials static final String USER = "root"; static final String PASS = "password"; // Set response content type response.setContentType("text/html"); PrintWriter out = response.getWriter(); String title = "Database Result"; String docType = "<!doctype html public -//w3c//dtd html 4.0 " + "transitional//en>\n"; out.println(docType + "<html>\n" + "<head><title>" + title + "</title></head>\n" + "<body bgcolor = #f0f0f0>\n" + "<h1 align = center>" + title + "</h1>\n"); try { // Register JDBC driver Class.forName("com.mysql.jdbc.Driver"); // Open a connection Connection conn = DriverManager.getConnection(DB_URL, USER, PASS); // Execute SQL query Statement stmt = conn.createStatement(); String sql; sql = "SELECT id, first, last, age FROM Employees"; ResultSet rs = stmt.executeQuery(sql); // Extract data from result set while(rs.next()){ //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getString("last"); //Display values out.println("ID: " + id + "<br>"); out.println(", Age: " + age + "<br>"); out.println(", First: " + first + "<br>"); out.println(", Last: " + last + "<br>"); } out.println("</body></html>"); // Clean-up environment rs.close(); stmt.close(); conn.close(); } catch(SQLException se) { //Handle errors for JDBC se.printStackTrace(); } catch(Exception e) { //Handle errors for Class.forName e.printStackTrace(); } finally { //finally block used to close resources try { if(stmt!=null) stmt.close(); } catch(SQLException se2) { } // nothing we can do try { if(conn!=null) conn.close(); } catch(SQLException se) { se.printStackTrace(); } //end finally try } //end try } }
现在让我们编译上面的servlet并在web.xml中创建以下条目
.... <servlet> <servlet-name>DatabaseAccess</servlet-name> <servlet-class>DatabaseAccess</servlet-class> </servlet> <servlet-mapping> <servlet-name>DatabaseAccess</servlet-name> <url-pattern>/DatabaseAccess</url-pattern> </servlet-mapping> ....
现在使用URL http://localhost:8080/DatabaseAccess调用此servlet,它将显示以下响应 :
Database ResultID: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal