while（rs.next（））的例外情况

时间：2018-05-22 14:48:26

标签： java rest web jdbc

我在Web应用程序的后端有这段代码。它有时会在while（rs.next（））处抛出NullPointerException，有时会抛出SQLException在ResultSet也在while（rs.next（））关闭后不允许运行，但有时它不会抛出任何错误。谁知道问题是什么？ 

public HashSet<LocalDate> getAvailableDates(long listingNumber) throws SQLException{
    Statement statement = null;
    String getDatesAvail = "SELECT AVAILDATE FROM AVAILABILITY WHERE LISTINGNUM = " +listingNumber +";";
    HashSet<LocalDate> avail = new HashSet<LocalDate>();
    ResultSet rs = null;
    try {
        connect(); // Open dbConnection
        statement = dbConnection.createStatement();
        rs = statement.executeQuery(getDatesAvail);
        System.out.println(getDatesAvail);
        if (rs == null) {
            System.out.println("Result set is null for avail");
        }
        while(rs.next()) {
            avail.add(LocalDate.parse(rs.getString("AVAILDATE"), DateTimeFormatter.ofPattern("yyyy-MM-dd")));
        }
    } catch (SQLException e) {
        System.out.println(e.getMessage());
        e.printStackTrace();
        throw new SQLException();
    } finally {
        if (rs != null) {
            rs.close();
        }
        if (statement != null) {
            statement.close();
        }
        if (dbConnection != null) {
            dbConnection.close();
        }
    }
    return avail;
}

我的connect（）方法：

private void connect() {
    try {
        Class.forName(DB_DRIVER);
    } catch (ClassNotFoundException e) {
        System.out.println(e.getMessage());
    }

    try {
        dbConnection = DriverManager.getConnection( DB_CONNECTION, DB_USER, DB_PASSWORD);

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

}

这是NullPointerException的堆栈跟踪：

java.lang.NullPointerException
    at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:6309)
    at car_service.JDBCConnector.getAvailableDates(JDBCConnector.java:1170)
    at car_service.JDBCConnector.getListing(JDBCConnector.java:974)
    at car_service.ListingController.getListing(ListingController.java:347)
    at car_service.ListingController.lambda$6(ListingController.java:94)
    at spark.RouteImpl$1.handle(RouteImpl.java:72)
    at spark.http.matching.Routes.execute(Routes.java:61)
    at spark.http.matching.MatcherFilter.doFilter(MatcherFilter.java:130)
    at spark.embeddedserver.jetty.JettyHandler.doHandle(JettyHandler.java:50)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1568)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.server.Server.handle(Server.java:530)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:347)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:256)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:102)
    at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:247)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.produce(EatWhatYouKill.java:140)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:131)
    at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:382)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:708)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:626)
    at java.lang.Thread.run(Unknown Source)

以下是SQLException的堆栈跟踪：

java.sql.SQLException: Operation not allowed after ResultSet closed
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:965)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:861)
    at com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:743)
    at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:6288)
    at car_service.JDBCConnector.getAvailableDates(JDBCConnector.java:1170)
    at car_service.JDBCConnector.getListing(JDBCConnector.java:974)
    at car_service.ListingController.getListing(ListingController.java:347)
    at car_service.ListingController.lambda$6(ListingController.java:94)
    at spark.RouteImpl$1.handle(RouteImpl.java:72)
    at spark.http.matching.Routes.execute(Routes.java:61)
    at spark.http.matching.MatcherFilter.doFilter(MatcherFilter.java:130)
    at spark.embeddedserver.jetty.JettyHandler.doHandle(JettyHandler.java:50)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1568)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.server.Server.handle(Server.java:530)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:347)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:256)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:102)
    at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:247)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.produce(EatWhatYouKill.java:140)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:131)
    at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:382)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:708)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:626)
    at java.lang.Thread.run(Unknown Source)

1 个答案:

答案 0 :(得分：0)

您的代码不是线程安全的。您错误地将node <- df %>% distinct(author_id, vendor) %>% rename(id = author_id) %>% mutate(vendor = as.numeric(vendor)) %>% mutate(id = as.character(id)) edge <- df %>% group_by(topic_id) %>% expand(topic_id, from = author_id, to = author_id) %>% filter(from < to) %>% select(to, from, topic_id) %>% mutate_at(vars(to, from), as.character) tidy_net <- tbl_graph(nodes = node, edges = edge, directed = F) plot(tidy_net) 对象存储为成员变量。它应该是一个局部变量，并在该方法中打开和关闭，其下面有一个连接池。

相关问题
最新问题