第一次发帖，一个关于servlet使用数据源的多线程安全性问题
public class UserDaoImpl implements UserDAO {
/** 日志实例 */
private Logger logger = Logger.getLogger("UserDaoImpl");
/** 数据源实例 */
private DataSource ds = null;
private static UserDaoImpl userDaoImpl = null;
public static UserDaoImpl getInstance() {
userDaoImpl = new UserDaoImpl();
return userDaoImpl;
}
private UserDaoImpl() {
initDataSource();
}
public void initDataSource() {
try {
Context initialContext = new InitialContext();
Context evoContext = (Context)initialContext.lookup("java:/comp/evo");
ds = (DataSource)evoContext.lookup("java/ums");
} catch (NamingException e) {
logger.log(Level.INFO, "数据源初始化失败！");
e.printStackTrace();
}
}
/////////////////////////////主要方法////////////////////////////////////////////
@Override
public boolean addUser(User user) {
Connection conn = null;
PreparedStatement preparedStatement = null;
ResultSet rs = null;
String sql = null;
int rowCount = -1;//数据库改变的行号，初始化为-1
try {
conn = ds.getConnection();
sql = "INSERT INTO userinfo VALUES(?, ?, ?, ?, ?)";
preparedStatement = conn.prepareStatement(sql);
preparedStatement.setString(1, user.getUserId());
preparedStatement.setString(2, user.getPassword());
preparedStatement.setString(3, user.getUserName());
preparedStatement.setString(4, user.getUserCode());
preparedStatement.setString(5, user.getEmail());
rowCount = preparedStatement.executeUpdate(sql);
preparedStatement.close();
preparedStatement = null;
conn.close();
conn = null;
} catch (SQLException e) {
logger.log(Level.INFO, "添加用户操作异常！");
e.printStackTrace();
} finally {
try {
if (rs != null) {
rs.close();
rs = null;
}
if (preparedStatement != null) {
preparedStatement.close();
preparedStatement = null;
}
if (conn != null) {
conn.close();
conn = null;
}
} catch (SQLException e) {
logger.log(Level.INFO, "数据库连接释放异常！");
e.printStackTrace();
}
}
if (rowCount == 0 || rowCount == -1) {
return false;
} else {
return true;
}
}
@Override
public List<User> findAll() {
.............(代码略，类似于adduser方法)
}
public boolean getUser(String userId) {
.............(代码略，类似于adduser方法)
}
servlet代码：
@SuppressWarnings("serial")
public class FrontController extends HttpServlet {
UserDAO userDao;
public void init() throws ServletException {
userDao = UserDaoImpl.getInstance();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("get");
doPost(request, response);//将请求交由doPost()处理
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("post");
String action = request.getParameter("action");//获得用户请求的动作
if ("login".equals(action)) {
login(request, response);
} else if ("register".equals(action)) {
register(request, response);
} else if ("logout".equals(action)) {
logout(request, response);
} else {
response.sendError(404);
}
}
public void login(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
。。。。。。。
userDao.getUser();
。。。。。。。
}
public void register(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
。。。。。。(代码略)
userDao.addUser(user);
。。。。。。(代码略)
}
public void logout(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
。。。。。。(代码略)
}
}
想问一下 这样会不会有多线程安全的问题？
[解决办法]
肯定会有问题，你在servlet中把userdao定义为一个成员变量，如果把这个变量变为一个局部变量，也就是放到dopost中就不会有问题了！
