元数据

元数据指的是数据的数据,建议操作时用ojdbc7.jar，其他版本的jar包可能对某些方法不支持！
分为三类：
1.数据库元数据（DataBaseMetaData）
（借助Connection获取元数据）

public static void databaseMetaData()  {
     
    try {
     
        Class.forName(DRIVERE);
        Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
        //数据库元信息
        DatabaseMetaData dbMetadata = connection.getMetaData() ;
        String dbName = dbMetadata.getDatabaseProductName();
        System.out.println("数据库名："+dbName);
        String dbVersion = dbMetadata.getDatabaseProductVersion();
        System.out.println("数据库版本："+dbVersion);

        String driverName = dbMetadata.getDriverName() ;
        System.out.println("驱动名"+driverName);
        String url = dbMetadata.getURL();
        System.out.println("驱动："+url);
        String userName = dbMetadata.getUserName();
        System.out.println("用户名："+userName);

       //先要设置主键 alter table account add constraint ps_id primary key(carid);
        //alter table student add constraint pk_id primary key(stuno);
        System.out.println("--------------------------------");
        ResultSet rs = dbMetadata.getPrimaryKeys(null,"SCOTT","STUDENT");
        while (rs.next()){
     
            System.out.println("123");
            Object tableName = rs.getObject(3);//表名
            Object columnName  = rs.getObject(4);//列名称
            Object pkName = rs.getObject(6);//主键的约束名称
            System.out.println(tableName+"========="+columnName+"========"+pkName);
        }

    }catch (Exception e){
     
        e.printStackTrace();
    }

}

结果：

2.参数元数据（ParameterMetaData）
（借助PreparedStatement）

public static void parameterMetaData(){
     
    try{
     
        Class.forName(DRIVERE);
        Connection connection = DriverManager.getConnection(URL,USERNAME,PASSWORD);
        String sql = "select *from student where stuno = ? and stuname = ?";
        PreparedStatement pstmt = connection.prepareStatement(sql);
        //通过pstmt获取参数元数据
        ParameterMetaData metaData = pstmt.getParameterMetaData();
        int count = metaData.getParameterCount();
        System.out.println("参数个数："+count);
        for(int i=1;i<=count;i++){
     
            String typeName = metaData.getParameterTypeName(i);
            System.out.println(typeName);//jdbc7
        }

    }catch (Exception e){
     
        e.printStackTrace();
    }
}

结果：

3.结果集元数据（ResultSetMetaData）
(借助ResultSet)

public static void resultSetMetaData(){
     
    try{
     
        Class.forName(DRIVERE);
        Connection connection = DriverManager.getConnection(URL,USERNAME,PASSWORD);
        PreparedStatement pstmt = connection.prepareStatement("select *from student");
        ResultSet rs = pstmt.executeQuery();
        ResultSetMetaData metaData = rs.getMetaData();
        int count = metaData.getColumnCount();//返回列数
        System.out.println("列数为："+count);
        System.out.println("---------------------------");
        for(int i=1;i<=count;i++){
     
            String columnName = metaData.getColumnName(i);
            String columnTypeName = metaData.getColumnTypeName(i);
            System.out.println(columnName+"\t"+columnTypeName);
        }
        System.out.println("------------------------");
        while(rs.next()){
     
            for(int i=1;i<=count;i++){
     
                System.out.print(rs.getObject(i)+"  ");
            }
            System.out.println();
        }
    }catch (Exception e){
     
        e.printStackTrace();
    }

}

结果：