JDBC的使用-----Statement

Posted 2021-02-17 QM.C

JDBC的查询步骤
1.加载数据库驱动类
	1)在工程下新建lib文件夹，将 ojdbc6.jar（jar包在：E:oracleproduct11.2.0dbhome_1jdbclib）拷贝至该目录下
	2)右键ojdbc6.jar文件，build path --> add too build path
	3)将驱动类加载到内存中
		Class.forName("oracle.jdbc.driver.OracleDriver");
2.获取数据库连接对象
	Connection conn = DriverManager.getConnection(url,user,password);
3.写sql
	String sql = "xxxxxx";
4.创建PreparedStatement对象
	PreparedStatement ps  = conn.prepareStatement(sql);
5.执行查询返回ResultSet结果集对象
	ResultSet rs = ps.executeQuery();
6.遍历结果集，获取查询结果
	while(rs.next){
		rs.getXxx()
	}
7.释放资源
	rs.close()
	ps.close()
	conn.close()
JDBC连接字符串
mysql：
String Driver="com.mysql.jdbc.Driver"; //驱动程序
String URL="jdbc:mysql://localhost:3306/db_name"; //连接的URL,db_name为数据库名
String Username="username"; //用户名
String Password="password"; //密码
Class.forName(Driver);
Connection con=DriverManager.getConnection(URL,Username,Password);

Oracle:
String Driver="oracle.jdbc.driver.OracleDriver";  //连接数据库的方法
String URL="jdbc:oracle:thin:@localhost:1521:orcl";  //orcl为数据库的SID
String Username="username"; //用户名
String Password="password"; //密码
Class.forName(Driver) ; //加载数据库驱动
Connection con=DriverManager.getConnection(URL,Username,Password); //常用数据库链接方式

DB2：
String Driver="com.ibm.dbjdbc.app.DBDriver"; //连接具有DB2客户端的Provider实例
//String Driver="com.ibm.dbjdbc.net.DBDriver"; //连接不具有DB2客户端的Provider实例
String URL="jdbc:db2://localhost:5000/db_name"; //db_name为数据库名
String Username="username"; //用户名
String Password="password"; //密码
Class.forName(Driver) ;



import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class TestStatement {
    public static void main(String[] args) {
        try {
            //1.加载数据库驱动文件
            Class.forName("oracle.jdbc.driver.OracleDriver");
            
            //2。获取数据库连接对象
            String url = "jdbc:oracle:thin:@127.0.0.1:1521:orcl";
            String user ="SCOTT";
            String password = "tiger";
            
            Connection conn = DriverManager.getConnection(url, user, password);
            
            //3.通过connection对象获取一个Statement对象，用于sql语句发送到数据库
            
            testExecuteQuery(conn.createStatement());
            System.out.println("--------------------");
            testExecuteUpdate(conn.createStatement());
            System.out.println("---------------------");
            testExcute(conn.createStatement());
            
        
            //5.遍历结果集
            
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("请检查连接驱动类是否正确");
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    public static void testExecuteUpdate(Statement stmt) throws SQLException {
        
        String sql = "insert into emp(empno,ename,sal) values(434,‘mm‘,5000)";
        int result = stmt.executeUpdate(sql);
        System.out.println(result);
    }

    public static void testExecuteQuery(Statement stmt) throws SQLException {
        //4.获取结果集对象
        //executeQuery 只能用在select关键字的查询中
        String sql = "select e.ename ee,e.empno from emp e";
        ResultSet rs = stmt.executeQuery(sql);
        while(rs.next()) {
            System.out.println(rs.getString("ee")+"	"+rs.getInt("empno"));
        }
    }
    
    public static void testExcute(Statement stmt) throws SQLException {
        //execute方法可以执行任意的sql语句
        String sql = "select * from emp";
        boolean flag = stmt.execute(sql);
        ResultSet rs = stmt.getResultSet();
        System.out.println(flag);
        
        while(rs.next()) {
            System.out.println(rs.getString("empno"));
        }
        
    }
}

 

import java.sql.Connection;import java.sql.DatabaseMetaData;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;
public class TestJDBCgetTable {public static void main(String[] args) {Connection conn = null;ResultSet columns = null;try {//加载数据库驱动文件Class.forName("oracle.jdbc.driver.OracleDriver");conn = DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:orcl", "SCOTT", "tiger");//获取数据库的元信息DatabaseMetaData metaData = conn.getMetaData();//查看数据库中有哪些表/*ResultSet rs = metaData.getTables(conn.getCatalog(), "SCOTT", null, new String[]{"TABLE"});while(rs.next()) {System.out.println(rs.getString(3));}*/columns = metaData.getColumns(conn.getCatalog(), "SCOTT", "EMP", null);while(columns.next()) {System.out.println(columns.getString(4));}} catch (ClassNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();}finally {try {if(columns!=null) {columns.close();}} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();}try {if(conn!=null) {conn.close();}} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}