JDBC1

com.learn.jdbc; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import org.junit.Test; public class Demo1 { Connection conn = null; @Test public void test() { try { //注册驱动 Class.forName("com.mysql.jdbc.Driver"); //获得连接 String url = "jdbc:mysql///mydatebase"; String user = "root"; String password = "root"; conn = DriverManager.getConnection(url, user, password); } catch (Exception e) { e.printStackTrace(); //释放资源 if( conn != null) { try { conn.close(); } catch (SQLException e1) { e1.printStackTrace(); } //垃圾回收尽快回收对象 conn = null; } } } }

2.JDBC的API

　　connection

 

 

　　statement

3.JDBC的元数据MataDate(提高通用性较高的代码)

• DatabaseMetaData：获得数据库连接的信息,获得数据库的表的信息.

* 获得数据库元数据:Connection中getMetaData();

 

• ParameterMetaData：获得SQL中的参数的个数及类型.

* 获得参数元数据：PreparedStatement中getParameterMetaData()

 

• ResultSetMetaData：获得结果集中的列名及列的类型.

* 获得结果集元数据：ResultSet中getMeta()

4.元数据的使用

public void demo2(){
        Connection conn = null;
        conn = JDBCUtils2.getConnection();
        // 获得数据库元数据:
        try {
            DatabaseMetaData metaData = conn.getMetaData();
            System.out.println("获得驱动名称:"+metaData.getDriverName());
            System.out.println("获得驱动URL:"+metaData.getURL());
            System.out.println("获得用户名:"+metaData.getUserName());
            
            // 获得表中的主键：
            ResultSet rs = metaData.getPrimaryKeys(null, null, "category");
            if(rs.next()){
                String name = rs.getString("COLUMN_NAME");
                System.out.println(name);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

参数元数据

　　

public void demo3(){
        Connection conn = null;
        PreparedStatement stmt = null;
        try{
            conn = JDBCUtils2.getConnection();
            String sql = "update category set cname = ? where cid = ?";
            stmt = conn.prepareStatement(sql);
            ParameterMetaData metaData = stmt.getParameterMetaData();
            int count = metaData.getParameterCount();
            System.out.println(count);
        }catch(Exception e){
            
        }
    }

结果集元数据

public void demo4(){
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try{
            conn = JDBCUtils2.getConnection();
            String sql = "select * from category";
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            
            ResultSetMetaData metaData = rs.getMetaData();
            int count = metaData.getColumnCount();
            for(int i = 1;i<=count ;i++){
                String name = metaData.getColumnName(i);
                
                String type = metaData.getColumnTypeName(i);
                System.out.println(name+type);
            }
        }catch(Exception e){
            
        }
    }

 

JDBC1

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