java 中的每个 sql 语句是否创建一个数据库连接

Question

我在我的实用程序连接中放置了以下内容，这将让我知道连接是从哪里创建的。

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

当我运行我的 class 下有 3 个 select (Preparedstatements)sql 语句时，我看到正在创建 3 个连接。

请告诉我这是正常现象，还是我做错了什么？？

这是我的工具class

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请求之后我得到了以下信息在我的服务器控制台中

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)

如果这是正常行为或者我的代码有什么问题，请告诉我？？

Answer 1

是的。

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

通常我们需要一个连接池系统。我们打开假设 5 个连接，然后我们使用可用的连接。如果您使用 Hibernate 或 Ibatis，它们会为您创建和管理连接池。希望对您有所帮助。

java 中的每个 sql 语句是否创建一个数据库连接

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