Servlet數據庫訪問
Servlets數據庫訪問實例代碼 - 詳細介紹關於如何使用Servlets訪問數據庫和使用JDBC和環境的設置。
本教學假定你已經了解JDBC應用程序的工作方式。通過一個servlet的數據庫訪問開始之前，確保你有適當的JDBC環境的設置和數據庫能正常使用。
對於更詳細關於如何訪問數據庫使用JDBC和環境的設置，可以通過JDBC教學。
基本概念下手，讓我們創建一個簡單的表並創建該表中的記錄數如下：
創建數據庫表
要在測試數據庫TEST中創建Employees表，請使用下列步驟：
Step 1:
打開命令提示符並更改進入到安裝目錄如下：
C:\> C:\>cd Program Files\MySQL\bin C:\Program Files\MySQL\bin>
Step 2:
登錄到數據庫，如下所示：
C:\Program Files\MySQL\bin>mysql -u root -p Enter password: ******** mysql>
Step 3:
在測試數據庫TEST中創建Employee表如下：
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>
創建數據記錄
最後，你創建幾個EMPLOYEE表插入數據如下：
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>
訪問數據庫:
下麵是一個例子，它展示了如何使用Servlet訪問的測試數據庫。
// 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 - by www.gitbook.net
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
conn = DriverManager.getConnection(DB_URL,USER,PASS);
// Execute SQL query
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
}
}
現在讓我們來編譯上麵的servlet在web.xml文件中創建以下條目:
....
<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>
....
現在使用URL: http://localhost:8080/DatabaseAccess將顯示以下回應調用這個servlet結果：
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
