What are the steps to connect to the database using jdbc?
The steps for jdbc to connect to the database: 1. Load the jdbc driver; 2. Create a database connection; 3. Create a preparedStatement; 4. Execute SQL statements; 5. Traverse the result set; 6. Handle exceptions and close JDBC Object resources.
The operating environment of this article: windows10 system, java 1.8, thinkpad t480 computer.
JDBC connects to the database and creates a program to connect to the database with JDBC, including the following steps:
First prepare the four parameters required by JDBC (user, password, url, driverClass)
(1) user name
(2) password
(3) URL defines the protocol, sub-protocol, and data source identifier when connecting to the database. Separate with colons. Writing form: Protocol: Subprotocol: Data source identifier
Protocol: Always starts with jdbc in JDBC
Subprotocol: It is the driver of the bridge connection or the name of the database management system.
Data source identification: Mark the address and connection port where the database source is found.
For example: (MySql connection URL)
jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=gbk
useUnicode=true: Indicates the use of the Unicode character set. If characterEncoding is set to gb2312 or GBK, this parameter must be set to true. characterEncoding=gbk: character encoding method.
For example:
try{//加载MySql的驱动类
Class.forName("com.mysql.jdbc.Driver") ;
}catch(ClassNotFoundException e){
System.out.println("找不到驱动程序类 ，加载驱动失败！");
e.printStackTrace() ;
} •Use DriverManager’s getConnectin(String url, String username, String password) method to obtain the path to the specified database to be connected, the username and password of the database.
//连接MySql数据库，用户名和密码都是root
String url = "jdbc:mysql://localhost:3306/test" ;
String username = "root" ;
String password = "root" ;
try{
Connection con = DriverManager.getConnection(url , username , password ) ;
}catch(SQLException se){
System.out.println("数据库连接失败！");
se.printStackTrace() ;
} 1. Execute static SQL statements. Usually implemented through Statement instances.
2. Execute dynamic SQL statements. Usually implemented through a PreparedStatement instance.
3. Execute the database stored procedure. Usually implemented through a CallableStatement instance.
•Specific implementation method:
Statement stmt = con.createStatement();
PreparedStatement pstmt = con.prepareStatement(sql);
CallableStatement cstmt = con.prepareCall("{CALL demoSp(? , ?)}") ;
1. ResultSet executeQuery( String sqlString): Execute the SQL statement to query the database and return a result set (ResultSet) object.
2. int executeUpdate(String sqlString): used to execute INSERT, UPDATE or DELETE statements and SQL DDL statements, such as: CREATE TABLE and DROP TABLE, etc.
3. execute(sqlString): used to execute multiple returns Statements with result sets, multiple update counts, or a combination of both.
• Specific implementation code:
ResultSet rs = stmt.executeQuery("SELECT * FROM ...");
int rows = stmt.executeUpdate("INSERT INTO ...");
boolean flag = stmt.execute(String sql);
两种情况：
1、执行更新返回的是本次操作影响到的记录数。
2、执行查询返回的结果是一个ResultSet对象。
• ResultSet包含符合SQL语句中条件的所有行，并且它通过一套get方法提供了对这些
行中数据的访问。
• 使用结果集（ResultSet）对象的访问方法获取数据：
while(rs.next()){
String name = rs.getString("name") ;
String pass = rs.getString(1) ; // 此方法比较高效
}
（列是从左到右编号的，并且从列1开始）
6、处理异常，关闭JDBC对象资源
•操作完成以后要把所有使用的JDBC对象全都关闭，以释放JDBC资源，关闭顺序和声 明顺序相反：
1、先关闭requestSet
2、再关闭preparedStatement
3、最后关闭连接对象connection
if(rs !=null){ // 关闭记录集
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(stmt !=null){ // 关闭声明
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(conn !=null){ // 关闭连接对象
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}相关视频教程：java视频教程
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