Question

我在实用程序连接中提供了以下信息，它会让我知道连接的创建位置。

 StackTraceElement[] st = Thread.currentThread().getStackTrace();
 System.out.println(  "create connection called from " + st[2] );

当我运行我的类时，有3个select（Preparedstatements）sql语句，我看到正在创建3个连接。

请让我知道这是正常的行为，还是我做错了什么？

这是我的实用程序类

public class DBConnection {

    public static Connection getDBConnection() {
        String sURL="jdbc:mysql://localhost:3306/XXX";
        String sUserName="root";
        String sPwd="";
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(sURL, sUserName,sPwd);

                 StackTraceElement[] st = Thread.currentThread().getStackTrace();
                System.out.println(  "create connection called from " + st[2] );

            return conn;
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return conn;
    }


    public static void close(Connection con)
    {
        if (con != null)
        {
            try
            {
                con.close();
            }
            catch (SQLException e)
            {
                e.printStackTrace();
            }
        }
    }

    public static void close(Statement stmt, ResultSet rs) 
    {
        if (rs != null)
        {
            try
            {
                rs.close();
            }
            catch (SQLException e)
            {
                e.printStackTrace();
            }
        }
        if (stmt != null)
        {
            try
            {
                stmt.close();
            }
            catch (SQLException e)
            {
                e.printStackTrace();
            }
        }
    }
}

这是我的java文件

public class Services {

    public String getData(@QueryParam("test") String test)
    {
        Connection dbConnection = null;
        PreparedStatement preparedStmt1 = null;
        ResultSet ResultSet1 = null;
        PreparedStatement custIdPst = null;
        ResultSet ResultSet2 = null;
        PreparedStatement activeRestPst = null;
        ResultSet activeRestResultSet = null;
        try
        {
            dbConnection = DBConnection.getDBConnection();
            String sql = "select xxxx from xxx";
            preparedStmt1 = dbConnection.prepareStatement(sql);
            ResultSet1 = preparedStmt1.executeQuery();
            while(ResultSet1.next())
            {
            // do something
            }
            String sqlcustid = "select xxx from xxx? limit 1;";
            while(ResultSet2.next())
            {

            }
            for(String str : list)
            {
                try
                {
                    String sqlactiveresta = "select xxx from xxx ?";
                    activeRestResultSet = activeRestPst.executeQuery();
                    while(activeRestResultSet.next())
                    {
                    }

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

            }

        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            DBConnection.close(preparedStmt1,ResultSet1);
            DBConnection.close(custIdPst,ResultSet2);
            DBConnection.close(activeRestPst,activeRestResultSet);
            DBConnection.close(dbConnection);
        }

    }

}

我问的原因是因为在一些要求后我得到了以下内容在我的服务器控制台

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"
        at sun.reflect.GeneratedConstructorAccessor42.newInstance(Unknown Source)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
        at com.mysql.jdbc.Util.getInstance(Util.java:386)

请告诉我这种正常行为或我的代码是否有任何问题？

Answer 1

是

每次创建DriverManager.getConnection（sURL，sUserName，sPwd）时都会创建一个连接。

通常我们需要一个连接池系统。我们打开让5个连接，然后我们使用可用的连接。如果您使用Hibernate或Ibatis，他们会为您创建和管理连接池。希望这有帮助。

java中的每个sql语句都会创建数据库连接

1 个答案: