java持久层_java访问持久层技术的进化
１. pojo(简单的java，直接访问DB)
A. 导入所需的jar包
import com.mysql.jdbc.Connection;
import com.mysql.jdbc.PreparedStatement;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
B. 获取与数据库的连接
private static Connection getConn() {
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/samp_db";
String username = "root";
String password = "";
Connection conn = null;
try {
Class.forName(driver); //classLoader,加载对应驱动
conn = (Connection) DriverManager.getConnection(url, username, password);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
C.拿着连接cnn去操作数据库获取PreparedStatement
private static Integer getAll() {
Connection conn = getConn();
String sql = "select * from students";
PreparedStatement pstmt;
try {
pstmt = (PreparedStatement)conn.prepareStatement(sql);
ResultSet rs = pstmt.executeQuery();
int col = rs.getMetaData().getColumnCount();
System.out.println("============================");
while (rs.next()) {
for (int i = 1; i <= col; i++) {
System.out.print(rs.getString(i) + "\t");
if ((i == 2) && (rs.getString(i).length() < 8)) {
System.out.print("\t");
}
}
System.out.println("");
}
System.out.println("============================");
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
２．spring jdbcTemplate(jdbc模板访问DB)
A. 配置数据源-applicationcontext.xml
B. 配置连接池-applicationcontext.xml
C. 注入java中并使用
@Autowired
private JdbcTemplate jdbcTemplate;
.....
String sql = "SELECT * FROM stu"
return jdbcTemplate.queryForList(sql);
3. ORM技术框架(对象-关系映射技术)
3.1 MyBatis(前身是iBatis)
另见博客！：https://my.oschina.net/u/3697586/blog/1924307
3.2 Hibernate
3.3 JPA