JDBC programming steps
- Load the driver:
Class.forName(driverClass)
//加载MySql驱动
Class.forName("com.mysql.jdbc.Driver")
//加载Oracle驱动
Class.forName("oracle.jdbc.driver.OracleDriver")
- Get a database connection:
DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/admin4j", "root", "root");
3. Create a Statement\PreparedStatement object:
conn.createStatement();
conn.prepareStatement(sql);
4. execute sql
execute()
full example
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class DbUtil {
public static final String URL = "jdbc:mysql://localhost:3306/admin4j";
public static final String USER = "admin4j";
public static final String PASSWORD = "123456";
public static void main(String[] args) throws Exception {
//1.加载驱动程序
Class.forName("com.mysql.jdbc.Driver");
//2. 获得数据库连接
Connection conn = DriverManager.getConnection(URL, USER, PASSWORD);
//3.操作数据库，实现增删改查
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT user_name, age FROM admin4j_goddess");
//如果有数据，rs.next()返回true
while(rs.next()){
System.out.println(rs.getString("user_name")+" 年龄："+rs.getInt("age"));
}
}
}
CRUD
//定义工具类
public class DbUtil {
public static final String URL = "jdbc:mysql://localhost:3306/admin4j";
public static final String USER = "liulxadmin4j
public static final String PASSWORD = "123456";
private static Connection conn = null;
static{
try {
//1.加载驱动程序
Class.forName("com.mysql.jdbc.Driver");
//2. 获得数据库连接
conn = DriverManager.getConnection(URL, USER, PASSWORD);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
public static Connection getConnection(){
return conn;
}
}
//定义实体
public class Goddess {
private Integer id;
private String user_name;
private Integer sex;
private Integer age;
private Date birthday; //注意用的是java.util.Date
private String email;
private String mobile;
private String create_user;
private String update_user;
private Date create_date;
private Date update_date;
private Integer isDel;
//getter setter方法。。。
}
DAO layer
public class GoddessDao {
//增加
public void addGoddess(Goddess g) throws SQLException {
//获取连接
Connection conn = DbUtil.getConnection();
//sql
String sql = "INSERT INTO admin4j_goddess(user_name, sex, age, birthday, email, mobile,"+
"create_user, create_date, update_user, update_date, isdel)"
+"values("+"?,?,?,?,?,?,?,CURRENT_DATE(),?,CURRENT_DATE(),?)";
//预编译
PreparedStatement ptmt = conn.prepareStatement(sql); //预编译SQL，减少sql执行
//传参
ptmt.setString(1, g.getUser_name());
ptmt.setInt(2, g.getSex());
ptmt.setInt(3, g.getAge());
ptmt.setDate(4, new Date(g.getBirthday().getTime()));
ptmt.setString(5, g.getEmail());
ptmt.setString(6, g.getMobile());
ptmt.setString(7, g.getCreate_user());
ptmt.setString(8, g.getUpdate_user());
ptmt.setInt(9, g.getIsDel());
//执行
ptmt.execute();
}
public void updateGoddess(){
//获取连接
Connection conn = DbUtil.getConnection();
//sql, 每行加空格
String sql = "UPDATE admin4j_goddess" +
" set user_name=?, sex=?, age=?, birthday=?, email=?, mobile=?,"+
" update_user=?, update_date=CURRENT_DATE(), isdel=? "+
" where id=?";
//预编译
PreparedStatement ptmt = conn.prepareStatement(sql); //预编译SQL，减少sql执行
//传参
ptmt.setString(1, g.getUser_name());
ptmt.setInt(2, g.getSex());
ptmt.setInt(3, g.getAge());
ptmt.setDate(4, new Date(g.getBirthday().getTime()));
ptmt.setString(5, g.getEmail());
ptmt.setString(6, g.getMobile());
ptmt.setString(7, g.getUpdate_user());
ptmt.setInt(8, g.getIsDel());
ptmt.setInt(9, g.getId());
//执行
ptmt.execute();
}
public void delGoddess(){
//获取连接
Connection conn = DbUtil.getConnection();
//sql, 每行加空格
String sql = "delete from admin4j_goddess where id=?";
//预编译SQL，减少sql执行
PreparedStatement ptmt = conn.prepareStatement(sql);
//传参
ptmt.setInt(1, id);
//执行
ptmt.execute();
}
public List<Goddess> query() throws SQLException {
Connection conn = DbUtil.getConnection();
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT user_name, age FROM admin4j_goddess");
List<Goddess> gs = new ArrayList<Goddess>();
Goddess g = null;
while(rs.next()){
g = new Goddess();
g.setUser_name(rs.getString("user_name"));
g.setAge(rs.getInt("age"));
gs.add(g);
}
return gs;
}
public Goddess get(){
Goddess g = null;
//获取连接
Connection conn = DbUtil.getConnection();
//sql, 每行加空格
String sql = "select * from admin4j_goddess where id=?";
//预编译SQL，减少sql执行
PreparedStatement ptmt = conn.prepareStatement(sql);
//传参
ptmt.setInt(1, id);
//执行
ResultSet rs = ptmt.executeQuery();
while(rs.next()){
g = new Goddess();
g.setId(rs.getInt("id"));
g.setUser_name(rs.getString("user_name"));
g.setAge(rs.getInt("age"));
g.setSex(rs.getInt("sex"));
g.setBirthday(rs.getDate("birthday"));
g.setEmail(rs.getString("email"));
g.setMobile(rs.getString("mobile"));
g.setCreate_date(rs.getDate("create_date"));
g.setCreate_user(rs.getString("create_user"));
g.setUpdate_date(rs.getDate("update_date"));
g.setUpdate_user(rs.getString("update_user"));
g.setIsDel(rs.getInt("isdel"));
}
return g;
}
}
Similarities and differences between Statement and PreparedStatement
connect:
-
1. PreparedStatement inherits from Statement
-
2. Both PrerapedStatement and Statement are interfaces
-
3. Both PreParedStatement and Statement can implement CRUD operations on the data table: adding, deleting, modifying and checking
-
4. Both preparedstatement and statement are one of the APIs used to execute SQL query statements.
the difference:
1. The statement does not process the sql statement, and it is directly handed over to the database; while the prepraedstatement supports precompilation, and will put the compiled sql statement on the database side, which is equivalent to caching. For the sql statement that is executed repeatedly, you can use the prepraedstatement Make code execution more efficient.
2. Use the Statement object. When performing only one-time access to the database, use the Statement object for processing. The PreparedStatement object has more overhead than Statement and does not bring additional benefits for one-time operations.
3. Every time the statement executes a sql statement, the relevant database must execute the compilation of the sql statement. Preparedstatement is pre-compiled, and preparedstatement supports batch processing.
4. A JDBC program that executes many SQL statements generates a large number of Statement and PreparedStatement objects. It is generally considered that PreparedStatement objects are more efficient than Statement objects, especially if the same SQL statement is executed multiple times with different parameters. The PreparedStatement object allows the database to precompile SQL statements, which saves time and increases code readability in subsequent runs.
5. PreparedStatement can avoid the disadvantages of Statement: ① stringing ② sql injection problem
6. PreparedStatement can realize the operation of Blob type and Clob type data