- load driver
- get connection
- get statement and execute sql
- get resultSet and handle data
- close collections to database
Sample code:
review original JDBC operation for MySQL
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import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class OriginalConnection {
public static void main(String[] args) throws SQLException, ClassNotFoundException {
String url = "jdbc:mysql://localhost:3306/employee";
String user = "root";
String password = "alec";
Connection conn = null;
// avoid sql injection
PreparedStatement st = null;
ResultSet rs = null;
try {
// load driver for MySQL
// not recommended because it depends on database type
// DriverManager.registerDriver(new com.mysql.jdbc.Driver());
// below coding is strongly recommended, it depends on a string, not one
// database, good for extension and maintenance
// reflection, like framework works
Class.forName("com.mysql.jdbc.Driver");
// ----------------------------------------------------------------
// get connection
// import jdbc API for conn, not a specified database API, it is good for
// maintenace and switching database
// interface-oriented programming
conn = DriverManager.getConnection(url, user, password);
// ----------------------------------------------------------------
// get statement
String sql = "select id, name, password, birthday, email from user where name=?";
// pre-compile sql statement, can speed up execution and relieve database server
st = conn.prepareStatement(sql);
// 1 indicates the first "?"(placeholder)
// setString will check the validity of input, avoid sql injection
st.setString(1, "zhang");
// execute sql and get resultset
// note: do not set sql as a para, just run
// * rs.st.executeQuery(sql) *
rs = st.executeQuery();
// handle data
while (rs.next()) {
System.out.println(rs.getObject("id"));
System.out.println(rs.getObject("name"));
System.out.println(rs.getObject("password"));
System.out.println(rs.getObject("birthday"));
System.out.println(rs.getObject("email"));
}
} finally {
// close, reverse order compared with creating process
// To ensure the closing operation can be executed, these statements should be
// in clause "finally"
// To avoid closing operation occurs exception, add if and try/catch.
if (rs != null) {
try {
rs.close();
} catch (Exception e2) {
// catch exception, JVM go on below code
e2.printStackTrace();
}
rs = null;
}
if (st != null) {
try {
st.close();
} catch (Exception e3) {
// catch exception, JVM go on below code
e3.printStackTrace();
}
st = null;
}
if (conn != null) {
try {
conn.close();
} catch (Exception e4) {
// catch exception, JVM go on below code
e4.printStackTrace();
}
conn = null;
}
}
}
}
