jdbc 单例的问题

[java_8dc]

网上有很多人把jdbc连接数据库写成了单例模式，这种方式可行吗？ 多个线程都拿的是同一个Connection, 去操作数据库，这应该不行吧？
还有一个问题，如果用户只对数据库进行查询操作，那可不可以把Connection写成单例模式？
用人会用单例模式去获取一个数据库边接吗？ 如果有，那么用在什么场景？
感谢大家的讨论，谢谢！

[jumpheightway]

ThreadLocal吧

[victor_woo]

如果用户只对数据库进行查询操作，那可不可以把Connection写成单例模式？

一个连接可以有多个Statement对象并发支持多用户同时查询

[victor_woo]

查询一个连接 ，多Statement
更新一个连接,多Statement


事务处理多个连接

适用小型应用

[bb5209027]

JDBC 6个步骤：
1. Register driver
3 ways: * Class.forName(driverName);
* Driver dr=new XXXXDriver();
* java -Djdbc.drivers=driverName[:driverName] className

2. Establish a connection to the Database
2 ways * Connection con=DriverManager.getConnection(databaseURL, userID, password);
* Connection con=dr.connect(urlString, propertiesInfo);

3. Create a statement
3 statements:
* Statement st=con.createStatement();
* PreparedStatement pst=con.prepareStatement(sqlString);
* CallableStatement

4. Executing SQL
* st.execute(sqlString); //pst.setXXXX(?,?); pst.execute();
* ResultSet rs=st.executeQuery(sqlString); // pst.setXXXX(?,?); ResultSet rs=pst.executeQuery();
* st.executeUpdate(sqlString); // pst.setXXXX(?,?); pst.executeUpdate();

5. Processing ResultSet
while(rs.next())
XXX x= rs.getXXX(?);// !!!!!! data type (java <-> Sql ), ? : columnName|columnIndex

6. close : rs, st, pst, con
按这个来，一般据ok了

[xk1126]

干吗呀！真是的！
一般都写个类封装啊！~~

[火龙果被占用了]

不可行！

总之，如果在多线程处理上没有很强的技术，不能将数据库连接的那三个对象写成成员变量，更不能使用单例。

具体怎么不可行，需要看具体的代码。

[火龙果被占用了]

JDBC 规范并没有规定 Connection 必须是线程安全的，因此，JDBC 厂商也不会将其做为线程安全的。

[java_8dc]

请问火龙果
在不用连接池的情况下：
1. 那请问一个页面只有查询数据库的操作，也应该为每个请求创造一个Connection吗
2. 如果要为每个请求创建一个Connection，那我的JDBC连接应该写在什么地方？并且在什么地方关闭？
3. 如何做到当浏览器开启时创建连接，浏览器关闭时也断开连接？

[火龙果被占用了]

[Quote=引用 6 楼 java_8dc 的回复:]
请问火龙果
在不用连接池的情况下：
1. 那请问一个页面只有查询数据库的操作，也应该为每个请求创造一个Connection吗
2. 如果要为每个请求创建一个Connection，那我的JDBC连接应该写在什么地方？并且在什么地方关闭？
3. 如何做到当浏览器开启时创建连接，浏览器关闭时也断开连接？
[/Quote]

我想你应该知道 JDBC 代码的套路是什么，在这里我只能回答你，按照套路把 Connection 弄成局部变量。

[xiaohui5850]

Famous global IT company 上海
Position: Senior Java Software Engineer
Business Unit: Famous global IT company - BAS - China - ITSE

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Job Requirements
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 5+ years experience in requirements analysis, design, coding and testing of scalable, distributed, fault-tolerant applications.
 Expertise required in object-oriented design methodology and enterprise application development in Java .
 Hands-on experience with J2EE/J2SE application.
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