Java jdbc单例连接的通信异常

我期待在我的整个应用程序中使用单例jdbc连接。 当我启动tomcat从数据库中获取数据时，使用下面的代码，有时我会遇到下面的异常。 出了什么问题，我不明白，谁能提出什么可能的原因

例外情况：

com.mysql.cj.jdbc.exceptions.CommunicationsException: The last packet successfully received from the server was 65,128,558 milliseconds ago.  The last packet sent succ$
        at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:615)
        at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:57)
        at com.mysql.cj.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2011)
        at com.mysql.cj.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1826)
        at com.mysql.cj.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1923)
        at com.pradeep.sms.db.DBDataAccess.getDropdown(DBDataAccess.java:25)
        at com.pradeep.sms.controller.WebServicesController.getDropdown(WebServicesController.java:35)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:144)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:161)
        at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:160)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:99)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
        at org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:326)
        at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
        at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
        at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
        at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305)
        at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154)
        at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473)
        at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
        at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
        at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
        at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

独生子女班

我的申请课

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服务器未启动或主机错误。在web应用程序中使用单例连接检查代码中提供的服务器状态和主机名是没有意义的。阅读Tomcat文档，了解如何设置连接池和访问数据源以获得连接。错误表明连接以前工作过，但现在已停止工作。

public class DBConnection {
    private static String DB_DRIVER = "com.mysql.cj.jdbc.Driver";
    private static String DB_USER = "pradeep";
    private static String DB_PASSWORD = "12345678";
    private static String DB_NAME = "edusoft";
    private static String HOSTNAME = "host";
    private static String DB_PORT = "3306";
    private static String DB_CONNECTION = "jdbc:mysql://" + HOSTNAME + ":" + DB_PORT + "/" + DB_NAME + "?user="
            + DB_USER + "&password=" + DB_PASSWORD;

    private static final DBConnection ONLY_ONE = new DBConnection();
    private Connection con;
    private DBConnection() {
            try {
                Class.forName(DB_DRIVER);
                con = DriverManager.getConnection(DB_CONNECTION);// SQLException
            } catch (ClassNotFoundException | SQLException e) {
                e.printStackTrace();
            }
    }

    public static DBConnection getInstance() {
        return ONLY_ONE;
    }

    public Connection getcon() {
        return con;
    }
}

private Connection connection = DBConnection.getInstance().getcon();
    public String getDropdown(String dropdownName ) {

        String proCall="{call getDropdown(?)}";
        JSONObject jSONObject = new JSONObject();
        ArrayList<String> result = new ArrayList<String>();
        try {
            preparedStatement = connection.prepareStatement(proCall);
            preparedStatement.setString(1, dropdownName);

            resultSet= preparedStatement.executeQuery();
            while (resultSet.next()) {
                String classNames = resultSet.getString(1);
                result.add(classNames);
            }
            JSONArray jsArray = new JSONArray(result);
            jSONObject.put("rs", jsArray);

        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            if(resultSet!=null)
                try {
                    resultSet.close();
                } catch (SQLException e1) {
                    e1.printStackTrace();
                }
            if(preparedStatement !=null){
                try {
                    preparedStatement.close();  
                } catch (Exception e2) {

                }
            }
        }
        return jSONObject.toString();
    }