Question

我的应用程序已成功连接到mysql。但是我在运行时遇到这些控制台错误。我已经在下面的代码中指出了错误行：

（编辑）的

控制台错误：

bool

DBManger.java：

DB Manager 4....
DB Manager 5....
DB Manager 4....
DB Manager 5....
DB Manager 4....
DB Manager 5....
DB Manager 4....
DB Manager 5....
DB Manager 4....
DB Manager 5....
DB Manager 6....
DB Manager 7....
DB Manager 5....
DB Manager 4....

 java.sql.SQLException: Operation not allowed after ResultSet closed
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927)
        at com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:794)
        at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:838)
        at com.mysql.jdbc.ResultSetImpl.getObject(ResultSetImpl.java:4847)
        at agriya.talkr.db.DBManager.getObject(DBManager.java:270)
        at agriya.talkr.models.Settings.getSettings(Settings.java:62)
        at agriya.talkr.app.WebServices.doGet(WebServices.java:153)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
        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)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

DB Manager 1....
DB Manager 2....
DB Manager 3....
DB Manager 4....
DB Manager 5....
DB Manager 4....
DB Manager 5....

Settings.java：

public static Connection _connect = null;  
public static Statement _statement = null;  
 .......
 ........

  public static Connection getConnect(){
        try {
            Class.forName("com.mysql.jdbc.Driver");
            _connect = (Connection) DriverManager.getConnection(CONNECTION_STR);
            _statement = (Statement) _connect.createStatement();
        } catch (ClassNotFoundException e) {
            System.out.println("EX: " + e.getLocalizedMessage());
            return null;
        } catch (SQLException e) {
            System.out.println("EX: " + e.getLocalizedMessage());
            return null;
        }
        return _connect;
    }

    private static void prepareStatement(String query){
        try {
            if(_connect != null && !_connect.isClosed())
                _connect.close();
            _connect = getConnect();
            _preparedStatement = (PreparedStatement) _connect.prepareStatement(query);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }



 public static JSONObject getObject(String query){
       System.out.println("QUERY: " + query);
       _connect = getConnect();
       JSONObject json = new JSONObject();

       System.out.println("DB Manager 1....");
       try {

           System.out.println("DB Manager 2....");

            ResultSet rs =_statement.executeQuery(query);
            ResultSetMetaData md = rs.getMetaData();
            int columns = md.getColumnCount();
            while (rs.next()){

                  System.out.println("DB Manager 3....");

                 for(int i=1; i<=columns; ++i){       

                      System.out.println("DB Manager 4....");

                         json.put(md.getColumnName(i).toString(), 
                                  rs.getObject(i).toString()); --->270th line

                          System.out.println("DB Manager 5....");
                 }
            }
              System.out.println("DB Manager 6....");

            rs.close();

              System.out.println("DB Manager 7....");
            _connect.close();
       } 


       catch (SQLException e) {
           e.printStackTrace();
       } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 
       return json;
   }

WebServices.java：

公共类WebServices扩展了HttpServlet {

public static JSONObject getSettings(String phone_number){
        Settings s = (Settings) Settings.toObject(DBManager.getObject
       ("Select * from settings where user_id =" + phone_number), Settings.class); --->62nd line
        try {
            return new JSONObject(new Gson().toJson(s, Settings.class));
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return new JSONObject();
    }

任何人都可以帮助我。谢谢。

Answer 1

您的DBManager对Connection和statement使用静态变量。当接收并发请求时，一个请求可以关闭由另一个请求激活的连接和语句。

您可以使DBManger.getObject同步（这会因为同步请求而导致性能下降）或将_connection和_statement转换为局部变量：

public static JSONObject getObject(String query){
   try (Connection con = getConnect()) {
       Statement stmt = con.createStatement();
       ResultSet rs = stmt.executeQuery(query);
       ...
   }
}

Answer 2

您对_connect.close();的呼叫可能会在运行，而该循环的另一个实例仍处于活动状态 - 这很可能会关闭ResultSet并导致该错误。

对每个方法分配的内容使用静态变量通常很危险 - 因为您永远不知道何时可以重新分配值。

<强>修正

使用try-with-resource语法：

System.out.println("QUERY: " + query); try(Connection connect = getConnect(); Statement statement = connect.createStatement(); ResultSet rs = statement.executeQuery(query)) { ResultSetMetaData md = rs.getMetaData(); int columns = md.getColumnCount(); while (rs.next()){ System.out.println("DB Manager 3...."); for(int i=1; i<=columns; ++i){ System.out.println("DB Manager 4...."); json.put(md.getColumnName(i).toString(), rs.getObject(i).toString()); --->270th line System.out.println("DB Manager 5...."); } } System.out.println("DB Manager 6...."); System.out.println("DB Manager 7...."); } catch (SQLException e) { e.printStackTrace(); } catch (JSONException e) { // TODO Auto-generated catch block e.printStackTrace(); } return json; }

ResultSet关闭后不允许操作[SQL异常]

2 个答案: