JDBC（九）DatabaseMetaData 数据库元数据

通过java.sql.DatabaseMetaData 接口，我们能获取到数据库的列表、列等信息。

DatabaseMetaData 接口包含了许多方法，这里值介绍常用的。

###获取 DatabaseMetaData 实例对象

DatabaseMetaData databaseMetaData = connection.getMetaData();
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###获取数据库名和版本

int    majorVersion   = databaseMetaData.getDatabaseMajorVersion();
int    minorVersion   = databaseMetaData.getDatabaseMinorVersion();String productName    = databaseMetaData.getDatabaseProductName();
String productVersion = databaseMetaData.getDatabaseProductVersion();
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数据库属性信息：5 6 MySQL 5.6.24
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###获取数据库驱动版本

int driverMajorVersion = databaseMetaData.getDriverMajorVersion();
int driverMinorVersion = databaseMetaData.getDriverMinorVersion();
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###获取数据库列表

String   catalog          = null;
String   schemaPattern    = null;
String   tableNamePattern = null;
String[] types            = null;ResultSet result = databaseMetaData.getTables(catalog, schemaPattern, tableNamePattern, types );while(result.next()) {String tableName = result.getString(3);
}
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getTables()方法源码：

    ResultSet getTables(String catalog, String schemaPattern,String tableNamePattern, String types[]) throws SQLException;
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我在这里给四个参数都赋值null，则它会把所有数据库中的表信息返回。

此ResultSet包含10列，每列包含有关给定表的信息。索引3指的是表名称。

user
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###在表中列出列

String   catalog           = null;
String   schemaPattern     = null;
String   tableNamePattern  = "user";
String   columnNamePattern = null;ResultSet result = databaseMetaData.getColumns(catalog, schemaPattern,  tableNamePattern, columnNamePattern);while(result.next()){String columnName = result.getString(4);int    columnType = result.getInt(5);
}
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getColumns（）方法返回的ResultSet包含给定表的列的列表。索引为4的列包含列名称，索引为5的列包含列类型。列类型是一个与java.sql.Types中的类型常量匹配的整数。

id 4 
username 12 
birthday 91 
sex 1 
address 12 
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###表的主键

String   catalog   = null;
String   schema    = null;
String   tableName = "user";ResultSet result = databaseMetaData.getPrimaryKeys(catalog, schema, tableName);while(result.next()){String columnName = result.getString(4);
}
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调用getPrimaryKeys（）方法，向其传递3个参数。在这个例子中，只有tableName是非空的。

getPrimaryKeys（）方法返回的ResultSet包含组成给定表主键的列表。索引4指的是的列名称。

主键可以由多个列组成。这样的密钥被称为复合密钥。如果表包含复合键，则ResultSet将包含多行。复合键中的每一列都有一行。

id
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###全部代码

package com.jdbc;import java.sql.*;/*** Created by Fant.J.* 2018/3/5 21:38*/
public class DatabaseMetaDataTest {public static void main(String[] args) {String url = "jdbc:mysql://localhost:3306/user";String user = "root";String password = "root";Connection connection =null;try {Class.forName("com.mysql.jdbc.Driver");connection = DriverManager.getConnection(url,user,password);DatabaseMetaData databaseMetaData = connection.getMetaData();int    majorVersion   = databaseMetaData.getDatabaseMajorVersion();int    minorVersion   = databaseMetaData.getDatabaseMinorVersion();String productName    = databaseMetaData.getDatabaseProductName();String productVersion = databaseMetaData.getDatabaseProductVersion();System.out.println("数据库属性信息："+majorVersion+" "+minorVersion+" "+productName+" "+productVersion);int driverMajorVersion = databaseMetaData.getDriverMajorVersion();int driverMinorVersion = databaseMetaData.getDriverMinorVersion();System.out.println("驱动信息："+driverMajorVersion+" "+driverMinorVersion);/*            String   catalog          = null;String   schemaPattern    = null;String   tableNamePattern = null;String[] types            = null;ResultSet result = databaseMetaData.getTables(catalog, schemaPattern, tableNamePattern, types );while(result.next()) {String tableName = result.getString(3);System.out.println(tableName);}*//*           String   catalog           = null;String   schemaPattern     = null;String   tableNamePattern  = "user";String   columnNamePattern = null;ResultSet result = databaseMetaData.getColumns(catalog, schemaPattern,  tableNamePattern, columnNamePattern);while(result.next()){String columnName = result.getString(4);int    columnType = result.getInt(5);System.out.println(columnName+" "+columnType+" ");}*/String   catalog   = null;String   schema    = null;String   tableName = "user";ResultSet result = databaseMetaData.getPrimaryKeys(catalog, schema, tableName);while(result.next()){String columnName = result.getString(4);System.out.println(columnName);}} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}}
}复制代码