📅 最后修改于: 2020-11-12 05:42:26 🧑 作者: Mango
本教程假定您已了解JDBC应用程序的工作方式。在开始通过servlet进行数据库访问之前，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，请阅读JDBC教程。
首先，让我们创建一个简单的表，并在该表中创建一些记录，如下所示：
要在TEST数据库中创建雇员表，请使用以下步骤-
打开命令提示符，然后更改为安装目录，如下所示：
C:\>
C:\>cd Program Files\MySQL\bin
C:\Program Files\MySQL\bin>
登录数据库如下
C:\Program Files\MySQL\bin>mysql -u root -p
Enter password: ********
mysql>
在TEST数据库中创建表Employee ，如下所示-
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表中创建了几条记录，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，显示了如何使用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 =
""-//w3c//dtd html 4.0 " + "transitional//en\">\n";
out.println(docType +
"\n" +
"" + title + " \n" +
"\n" +
"" + title + "
\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 + "
");
out.println(", Age: " + age + "
");
out.println(", First: " + first + "
");
out.println(", Last: " + last + "
");
}
out.println("");
// 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
}
}
现在让我们在servlet上方进行编译，并在web.xml中创建以下条目
....
DatabaseAccess
DatabaseAccess
DatabaseAccess
/DatabaseAccess
....
现在使用URL http：// localhost：8080 / DatabaseAccess调用此servlet，它将显示以下响应-
Database Result
ID: 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