JDBC学习笔记

jdbc4.2 常用接口和类

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DriverManager

static synchronized Connection getConnection(url, user, pass)	//获取连接

Connection接口

//获取Statement才能执行SQL
Statement createStatement()
PreparedStatement prepareStatement(sql)
CallableStatement prepareCall(sql)
//控制事务的方法
Savepoint setSavepoint()
void setTransactionIsolation(level)	//设置事务的隔离级别
void rollback()	//回滚
void setAutoCommit(autoCommit)  //关闭自动提交，打开事务
void commit()	//提交

//java7 新增
setSchema(schema)	
setNetworkTimeout()

Statement接口

ResultSet executeQuery(sql)
int executeUpdate(sql)
boolean execute(sql) 	//如果执行后第一个结果为ResultSet对象，返回true
statement.getResultSet()
statement.getUpdateCount()
statement.getMetaData()	//获取结果集的元数据

PreparedStatement 是Statement的子接口，预编译的Statement对象

//效率更高、安全，防止SQL注入
void setXxx(parameterIndex, value)

//java8 新增
executeLargeUpdate() 	影响记录数超过Integer.MAX_VALUE时用此方法

ResultSet 结果集对象

//移动指针、关闭
void close()
boolean absolute(row)	记录指针移动到row行
void beforeFirst()		首行之前，初始状态
boolean first()
boolean previous()
boolean next()
boolean last()
void afterLast()

//获取值
getXxx(columnIndex)
<T> T getObject(columnIndex, Class<T> type)	获取任意类型的值，java7新增

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jdbc编程步骤

    Class.forName("com.mysql.cj.jdbc.Driver");
    try (
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai&useSSL=false"
		, "root", "123456");
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("select * from user;"))
    {
        while (resultSet.next()){
            System.out.println(resultSet.getInt(1) + "\t" + resultSet.getString(2) + "\t" + resultSet.getString(3)
            + "\t" + resultSet.getString(4));
        }

        String insertSql = "insert into user(user_name, password, sex) values(?, ?, ?)";
        PreparedStatement pStatement = connection.prepareStatement(insertSql);
        pStatement.setString(1, "刘德华");
        pStatement.setString(2, "1234444");
        pStatement.setInt(3, 1);
        pStatement.executeUpdate();
		
    } catch (SQLException e) {
        e.printStackTrace();
    }

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可更新的结果集

//创建Statement时传入参数
resultSetType:
ResultSet.TYPE_FORWARD_ONLY	jdk1.4之前默认值，只能向前移动
ResultSet.TYPE_SCROLL_INSENSITIVE	自由移动指针，底层数据改变不影响ResultSet内容
ResultSet.TYPE_SCROLL_SENSITIVE	自由移动指针，底层数据改变会影响
//需要底层数据库驱动的支持

resultSetConcurrency  	并发模型
ResultSet.CONCUR_READ_ONLY		默认，只读模式
ResultSet.CONCUR_UPDATABLE		可更新的并发模式

//代码
statement = connection.prepareStatement(sql, ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
//可更新结果集需满足条件：
1. 所有数据来自一个表
2. 选出的数据集必须包含主键列
resultSet.updateString(2, 'aaa');
resultSet.updateRow();			//提交更改

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处理Blob类型数据

Binary Long Object二进制长对象，保存图片、声音文件等大文件
插入数据：用PreparedStatement，方法setBinaryStream(parameterIndex, InputStream)	传入二进制输入流
获取数据：ResultSet的getBlob(columnIndex) 获取Blob对象，它的getBinaryStream()获取输入流，或getBytes()直接取出封装的二进制数据。
代码：
InputStream is = new FileInputStream(file);
preparedStatement.setBinaryStream(1, is, (int)file.length());
preparedStatement.execuateUpdate();
//获取
Blob imgBlob = rs.getBlob(1);
bytes[] rts = imgBlob.getBytes(1L, (int)imgBlob.length());

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元数据分析

ResultSetMetaData分析结果集
DatabaseMetaData分析数据库信息

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批量更新

代码：
boolean autoCommit = conn.getAutoCommit();	//保存之前的提交模式，后面用于恢复
conn.setAutoCommit(false);	//开启事务支持

Statemet stmt = conn.createStatement();
stmt.addBatch(sql1);
stmt.addBatch(sql2);

stmt.executeBatch();	//java8 新增executeLargeBatch方法，需要驱动支持
conn.commit();		//提交
conn.setAutoCommit(autoCommit);	//恢复

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RowSet、离线RowSet

（略）

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使用数据库连接池 C3P0:

    ComboPooledDataSource dataSource = new ComboPooledDataSource();
    dataSource.setDrverClass("com.mysql.cj.jdbc.Driver");
    dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai&useSSL=false");
    dataSource.setUser("root");
    dataSource.setPassword("123456");

    dataSource.setMaxPoolSize(10);
    dataSource.setMinPoolSize(1);
    dataSource.setMaxStatements(50);

    try (
            Connection connection = dataSource.getConnection();

            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery("select * from user;"))
    {
        while (resultSet.next()){
            System.out.println(resultSet.getInt(1) + "\t" + resultSet.getString(2) + "\t" + resultSet.getString(3)
                    + "\t" + resultSet.getString(4));
        }

        String insertSql = "insert into user(user_name, password, sex) values(?, ?, ?)";
        PreparedStatement pStatement = connection.prepareStatement(insertSql);
        pStatement.setString(1, "李四");
        pStatement.setString(2, "1234444");
        pStatement.setInt(3, 1);
        pStatement.executeUpdate();

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