上一篇博客介绍了如何使用JAVA连接数据库，那么这一篇将继续为大家介绍如何使用JDBC对数据库的增删改查(CRUD)操作。
这一篇博客中的示例将使用上一篇中生成的H2数据库文件。
查询
查询在数据库的操作中是很重要的，我们把数据保存在数据库中，就是为了我们在需要的时候能够快速、高效的查询出来。
/**
* 查询
*
* @throws Exception
*/
public void query() throws Exception
{
Connection conn = getConnection();
Statement statement = conn.createStatement();
ResultSet resultSet = statement
.executeQuery("SELECT USER_ID, USER_NAME FROM USER_INFO");
System.out.printf("%20s %50s\n", "USER_ID", "USER_NAME");
// 遍历结果集
while (resultSet.next())
{
System.out.printf("%20s %50s\n", resultSet.getString("USER_ID"),
resultSet.getString("USER_NAME"));
}
resultSet.close();
statement.close();
conn.close();
}
/**
* 通过用户编号查询
*
* @param userId
* @throws Exception
*/
public void queryById(String userId) throws Exception
{
Connection conn = getConnection();
// 动态参数使用PreparedStatement，使用Statement存在SQL注入风险
PreparedStatement statement = conn
.prepareStatement("SELECT USER_ID, USER_NAME FROM USER_INFO WHERE USER_ID = ?");
statement.setString(1, userId);
ResultSet resultSet = statement.executeQuery();
System.out.printf("%20s %50s\n", "USER_ID", "USER_NAME");
// 遍历结果集
while (resultSet.next())
{
System.out.printf("%20s %50s\n", resultSet.getString("USER_ID"),
resultSet.getString("USER_NAME"));
}
resultSet.close();
statement.close();
conn.close();
}修改
在这里，我讲增删改作为一类，同属于对数据库的修改操作，在例子中，也会发现，我们使用的方法完全相同，仅仅是SQL的区别。
/**
* 修改
*
* @param userId
* @param userName
* @throws Exception
*/
public void update(String userId, String userName) throws Exception
{
Connection conn = getConnection();
// 动态参数使用PreparedStatement，使用Statement存在SQL注入风险
PreparedStatement statement = conn
.prepareStatement("UPDATE USER_INFO SET USER_NAME = ? WHERE USER_ID = ?");
statement.setString(1, userName);
statement.setString(2, userId);
System.out.println("受影响的记录条数为：" + statement.executeUpdate());
statement.close();
conn.close();
}
/**
* 清空
*/
public void clear() throws Exception
{
Connection conn = getConnection();
Statement statement = conn.createStatement();
System.out.println("受影响的记录条数为："
+ statement.executeUpdate("DELETE USER_INFO"));
statement.close();
conn.close();
}完整示例
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
public class JDBCCRUDemo
{
/**
* 获得数据库连接
*
* @return
* @throws Exception
*/
public Connection getConnection() throws Exception
{
Class.forName("org.h2.Driver");
return DriverManager.getConnection("jdbc:h2:h2.db", "test", "123");
}
/**
* 查询
*
* @throws Exception
*/
public void query() throws Exception
{
Connection conn = getConnection();
Statement statement = conn.createStatement();
ResultSet resultSet = statement
.executeQuery("SELECT USER_ID, USER_NAME FROM USER_INFO");
System.out.printf("%20s %50s\n", "USER_ID", "USER_NAME");
// 遍历结果集
while (resultSet.next())
{
System.out.printf("%20s %50s\n", resultSet.getString("USER_ID"),
resultSet.getString("USER_NAME"));
}
resultSet.close();
statement.close();
conn.close();
}
/**
* 通过用户编号查询
*
* @param userId
* @throws Exception
*/
public void queryById(String userId) throws Exception
{
Connection conn = getConnection();
// 动态参数使用PreparedStatement，使用Statement存在SQL注入风险
PreparedStatement statement = conn
.prepareStatement("SELECT USER_ID, USER_NAME FROM USER_INFO WHERE USER_ID = ?");
statement.setString(1, userId);
ResultSet resultSet = statement.executeQuery();
System.out.printf("%20s %50s\n", "USER_ID", "USER_NAME");
// 遍历结果集
while (resultSet.next())
{
System.out.printf("%20s %50s\n", resultSet.getString("USER_ID"),
resultSet.getString("USER_NAME"));
}
resultSet.close();
statement.close();
conn.close();
}
/**
* 添加
*
* @param userId
* @param userName
* @throws Exception
*/
public void insert(String userId, String userName) throws Exception
{
Connection conn = getConnection();
// 动态参数使用PreparedStatement，使用Statement存在SQL注入风险
PreparedStatement statement = conn
.prepareStatement("INSERT INTO USER_INFO(USER_ID, USER_NAME) VALUES(?, ?)");
statement.setString(1, userId);
statement.setString(2, userName);
System.out.println("受影响的记录条数为：" + statement.executeUpdate());
statement.close();
conn.close();
}
/**
* 修改
*
* @param userId
* @param userName
* @throws Exception
*/
public void update(String userId, String userName) throws Exception
{
Connection conn = getConnection();
// 动态参数使用PreparedStatement，使用Statement存在SQL注入风险
PreparedStatement statement = conn
.prepareStatement("UPDATE USER_INFO SET USER_NAME = ? WHERE USER_ID = ?");
statement.setString(1, userName);
statement.setString(2, userId);
System.out.println("受影响的记录条数为：" + statement.executeUpdate());
statement.close();
conn.close();
}
/**
* 清空
*/
public void clear() throws Exception
{
Connection conn = getConnection();
Statement statement = conn.createStatement();
System.out.println("受影响的记录条数为："
+ statement.executeUpdate("DELETE USER_INFO"));
statement.close();
conn.close();
}
public static void main(String[] args) throws Exception
{
JDBCCRUDemo demo = new JDBCCRUDemo();
demo.insert("id111", "name111");
demo.insert("id222", "name222");
demo.insert("id333", "name333");
demo.insert("id444", "name444");
demo.insert("id555", "name555");
demo.query();
demo.queryById("id444");
demo.update("id222", "name1234");
demo.query();
demo.clear();
}
}运行结果：
受影响的记录条数为：1
受影响的记录条数为：1
受影响的记录条数为：1
受影响的记录条数为：1
受影响的记录条数为：1
USER_ID USER_NAME
id111 name111
id222 name222
id333 name333
id444 name444
id555 name555
USER_ID USER_NAME
id444 name444
受影响的记录条数为：1
USER_ID USER_NAME
id111 name111
id333 name333
id444 name444
id555 name555
id222 name1234
受影响的记录条数为：5
