Java JDBC 基础

JDBC API 包含以下几个核心部分:

1:JDBC 驱动

2:Connections (连接)

3:Statements (声明)

4:Result Sets (结果集)

JDBC: 打开数据库连接

Loading the JDBC Driver(加载数据库驱动)

在打开数据库连接前必须先加载数据库驱动

Class.forName("driverClassName");

Opening the Connection(打开连接)

String url = "jdbc:mysql://127.0.0.1:3306/appName";
String user = "root";
String password = "123456";
Connection connection = DriverManager.getConnection(url,user,password);

Closing the Connection(关闭连接)

connection.close();

JDBC:查询数据库

对数据库进行操作,你需要创建SQL Statement,然后发送至数据库,得到返回结果.

Statement statement = conn.createStatement(); 

创建Statement后执行查询

String sql = "select * from table";
ResultSet result = statement.executeQuery(sql); 

对结果集进行迭代

while(result.next()){
    String name = result.getString("name");
    int age = result.getInt("age");
}
//根据数据库字段名获取对应的数据
result.getString("columnName");
result.getInt("columnName");
result.getLong("columnName");
result.getDouble("columnName");
result.getBigDecimal("columnName");
//通过字段索引顺序获取字段数据，索引从1开始
result.getInt(1);
result.getString(2);
//通过字段名找到数据库对应字段索引的位置
int columnIndex = result.findColumn("columnName");

如果需要迭代大量数据,使用索引的效率要比查询字段名获取数据要快.

完成数据迭代后需要对resultSet和statement进行关闭.

result.close();
statement.close();

JDBC:更新数据库

更新数据库包含更新数据库记录和删除数据库记录

excuteUpdate()方法可以用来更新和删除数据库记录.

更新记录

Statement statement = conn.createStatement();
String  sql = "update table set name = ’name‘ where id = 1“；
int rowAffected = statement.executeUpdate(sql); 

rowsAffected代表有多少条记录被更新了.

删除记录

像上面那样更新直接执行sql语句

JDBC:结果集

创建结果集

可以通过执行Statement和PreparedStatement来创建结果集.

Statement statement = conn.createStatement();
String sql = "select * from table";
ResultSet result = statement.executeQuery(sql); 
 
PrepareStatement statement = conn.preparedStatement();
ResultSet result = statement.executeQuery(sql);

更新结果集

result.updateString("name","alex");
result.updateInt("age",33);
result.updatBigDecimal("cofficient",new BigDecimal("0.1343");
result.updateRow();

数据将在调用updateRow()方法后才将数据真正更新至数据库,如果updateRow()执行与事物中则需等到事物提交才将数据提交更新.

JDBC:PreparedStatement

PreparedStatement特性:

1. 更容易操作sql statement 参数

2. 可对preparedstatement的重用

3. 更容易的批处理

操作示例

String sql = "update people set firstname=? , lastname=? where id=?";
PreparedStatement preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, "Gary");
preparedStatement.setString(2, "Larson");
preparedStatement.setLong  (3, 123);
int rowsAffected = preparedStatement.executeUpdate();

创建PreparedStatement

String sql = "select * from people where firstname=? and lastname=?";
 
PreparedStatement preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, "John");
preparedStatement.setString(2, "Smith");
ResultSet result = preparedStatement.executeQuery();

PreparedStatement的重用

String sql = "update people set firstname=? , lastname=? where id=?";
PreparedStatement preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, "Gary");
preparedStatement.setString(2, "Larson");
preparedStatement.setLong  (3, 123);
 
int rowsAffected = preparedStatement.executeUpdate();
preparedStatement.setString(1, "Stan");
preparedStatement.setString(2, "Lee");
preparedStatement.setLong  (3, 456);
 
int rowsAffected = preparedStatement.executeUpdate();

JDBC:批量更新操作

Statement Batch Updates

Statement statement = null;
try{
     statement = conn.createStatement();
     statement.addBatch("update people set firstname='John' where id=123");
     statement.addBatch("update people set firstname='Eric' where id=456");
 
    int[] recordsAffected   = statement.executeBatch();
}finally{
    if(statent != null) statement.close();
}

PreparedStatement Batch Updates

String sql = "update people set firstname=? , lastname=? where id=?";
 
PreparedStatement preparedStatement = null;
try{
    preparedStatement =
            connection.prepareStatement(sql);
    preparedStatement.setString(1, "Gary");
    preparedStatement.setString(2, "Larson");
    preparedStatement.setLong  (3, 123);
 
    preparedStatement.addBatch();
 
    preparedStatement.setString(1, "Stan");
    preparedStatement.setString(2, "Lee");
    preparedStatement.setLong  (3, 456);
 
    preparedStatement.addBatch();
 
    int[] affectedRecords = preparedStatement.executeBatch();
 
}finally {
    if(preparedStatement != null) {
        preparedStatement.close();
    }
}

JDBC:事务

开始事务

conn.setAutoCommit(false);

事务回滚

conn.rollback();

提交事务

conn.commit();

示例

Connection connection = ...
try{
    connection.setAutoCommit(false);
    Statement statement1 = null;
    try{
        statement1 = connection.createStatement();
        statement1.executeUpdate(
            "update people set name='John' where id=123");
    } finally {
        if(statement1 != null) {
            statement1.close();
        }
    }
    Statement statement2 = null;
    try{
        statement2 = connection.createStatement();
        statement2.executeUpdate(
            "update people set name='Gary' where id=456");
    } finally {
        if(statement2 != null) {
            statement2.close();
        }
    }
    connection.commit();
} catch(Exception e) {
    connection.rollback();
} finally {
    if(connection != null) {
        connection.close();
    }
}