Question

Proviso：请不要将数据库用于以下内容。

我收到了一个封闭的套接字异常，我将其归因于在localhost上运行的leafnode的延迟。预计会有延迟，我只是不确定如何处理它。

我知道，从单独的CLI程序中，leafnode正确回复并且实用程序类正在运行。对于这个应用程序，我可以从glassfish日志中看到：

nntp: <68 <x1-QQumhvcthNpaS3eWCQlR7Bleszk@gwene.org>
nntp: <69 <x1-N15vT7mtEkMzewjHjlTmjzBSpFY@gwene.org>
nntp: <70 <x1-cfsH29WrlKvYMd+t1ohsVSekIy0@gwene.org>
nntp: <71 <x1-DaQK7LTcaCQP3O3Us+8HTxTDALQ@gwene.org>
nntp: <72 <x1-1+PG1MuOkVUmzmY2XWRAWCKwbD8@gwene.org>
nntp: <73 <x1-sXoWsN3I56qalgUJAuT6+jWCYLE@gwene.org>
nntp: <74 <x1-osEXmt5CXnwu3eVGVAb4e11PZnY@gwene.org>
nntp: <.
nntp: >QUIT
nntp: <205 Always happy to serve!
INFO: GOT MESSAGES AS SO..
INFO: [gnu.mail.providers.nntp.NNTPMessage@1e2218b, gnu.mail.providers.nntp.NNTPMessage@10838ec, gnu.mail.providers.nntp.NNTPMessage@d14f1b, gnu.mail.providers.nntp.NNTPMessage@1a0b187, gnu.mail.providers.nntp.NNTPMessage@e74409, gnu.mail.providers.nntp.NNTPMessage@123ce36, gnu.mail.providers.nntp.NNTPMessage@1b7515a, gnu.mail.providers.nntp.NNTPMessage@3e0a57, gnu.mail.providers.nntp.NNTPMessage@118d5e0, gnu.mail.providers.nntp.NNTPMessage@1819b07, gnu.mail.providers.nntp.NNTPMessage@1e91886, gnu.mail.providers.nntp.NNTPMessage@493ab5, gnu.mail.providers.nntp.NNTPMessage@1ad7ec5, gnu.mail.providers.nntp.NNTPMessage@15dbf8d, gnu.mail.providers.nntp.NNTPMessage@1cae695, gnu.mail.providers.nntp.NNTPMessage@1e86f47, gnu.mail.providers.nntp.NNTPMessage@e1d295, gnu.mail.providers.nntp.NNTPMessage@1c87547, gnu.mail.providers.nntp.NNTPMessage@18b9691, gnu.mail.providers.nntp.NNTPMessage@14a0c6f, gnu.mail.providers.nntp.NNTPMessage@765340, gnu.mail.providers.nntp.NNTPMessage@53b2e4, gnu.mail.providers.nntp.NNTPMessage@10597ed, gnu.mail.providers.nntp.NNTPMessage@396c01, gnu.mail.providers.nntp.NNTPMessage@1e1f03d, gnu.mail.providers.nntp.NNTPMessage@63410a, gnu.mail.providers.nntp.NNTPMessage@433231, gnu.mail.providers.nntp.NNTPMessage@1945928, gnu.mail.providers.nntp.NNTPMessage@696ea0, gnu.mail.providers.nntp.NNTPMessage@1dde855, gnu.mail.providers.nntp.NNTPMessage@1c0559e, gnu.mail.providers.nntp.NNTPMessage@352a35, gnu.mail.providers.nntp.NNTPMessage@660b04, gnu.mail.providers.nntp.NNTPMessage@15d401f, gnu.mail.providers.nntp.NNTPMessage@11cddfb, gnu.mail.providers.nntp.NNTPMessage@31917d, gnu.mail.providers.nntp.NNTPMessage@46be43, gnu.mail.providers.nntp.NNTPMessage@7523ed, gnu.mail.providers.nntp.NNTPMessage@89a405, gnu.mail.providers.nntp.NNTPMessage@6f5b1b, gnu.mail.providers.nntp.NNTPMessage@c649d6, gnu.mail.providers.nntp.NNTPMessage@19882d, gnu.mail.providers.nntp.NNTPMessage@3b8201, gnu.mail.providers.nntp.NNTPMessage@d44937, gnu.mail.providers.nntp.NNTPMessage@112e45c, gnu.mail.providers.nntp.NNTPMessage@14e8cfc, gnu.mail.providers.nntp.NNTPMessage@a15e3, gnu.mail.providers.nntp.NNTPMessage@22f041, gnu.mail.providers.nntp.NNTPMessage@1cb71d7, gnu.mail.providers.nntp.NNTPMessage@19ee882, gnu.mail.providers.nntp.NNTPMessage@1b2d490, gnu.mail.providers.nntp.NNTPMessage@1a16b05, gnu.mail.providers.nntp.NNTPMessage@79412e, gnu.mail.providers.nntp.NNTPMessage@a66063, gnu.mail.providers.nntp.NNTPMessage@10203ea, gnu.mail.providers.nntp.NNTPMessage@14f0db5, gnu.mail.providers.nntp.NNTPMessage@10ceef3, gnu.mail.providers.nntp.NNTPMessage@1bc33e, gnu.mail.providers.nntp.NNTPMessage@af5b1a, gnu.mail.providers.nntp.NNTPMessage@860956, gnu.mail.providers.nntp.NNTPMessage@1cf1146, gnu.mail.providers.nntp.NNTPMessage@1770fb1, gnu.mail.providers.nntp.NNTPMessage@1a76bc3, gnu.mail.providers.nntp.NNTPMessage@940c94, gnu.mail.providers.nntp.NNTPMessage@1c5d10c, gnu.mail.providers.nntp.NNTPMessage@1fa00d, gnu.mail.providers.nntp.NNTPMessage@44ecf0, gnu.mail.providers.nntp.NNTPMessage@11f88e8, gnu.mail.providers.nntp.NNTPMessage@1554648, gnu.mail.providers.nntp.NNTPMessage@17921a7, gnu.mail.providers.nntp.NNTPMessage@1905dbf, gnu.mail.providers.nntp.NNTPMessage@fad175]
INFO: ..GOT MESSAGES AS SO

NNTP消息最终会被加载。它只是它似乎没有及时回到bean，或者，如果它确实回来，它可能是bean的错误实例。我推断第一个bean通过正常，但另一个bean得到套接字问题因为Leafnode很忙。看起来bean构造函数被多次调用，这当然没问题，但可能就是第二个bean关闭套接字的原因。

那么，我如何隔离延迟问题，以便任何MessageBean获取，错误，？枚举单例？ javax.mail.Message的正确吗？（我使用的是GNU NNTP库，它比Apache好得多，而且工作正常。）

这是facelets客户端：

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE composition PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<ui:composition xmlns:ui="http://java.sun.com/jsf/facelets"
                template="./template.xhtml"
                xmlns:h="http://java.sun.com/jsf/html"
                xmlns:c="http://java.sun.com/jsp/jstl/core"
                xmlns:f="http://java.sun.com/jsf/core">
    <ui:define name="left">
        <h:button id="submit" value="click me" />
    </ui:define>
    <ui:define name="content">
        <ui:repeat value="#{messageBean.messages}" var="message">
            <li>
                <h:outputText value="#{message.messageNumber}" />
                <h:outputText value="#{message.subject}" />
            </li>
        </ui:repeat>
    </ui:define>
</ui:composition>

和支持MessageBean如此：

package net.bounceme.dur.nntp;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;
import javax.mail.Message;

@Named
@SessionScoped
public class MessageBean implements Serializable {

    private static final long serialVersionUID = 1;
    private static Logger logger = Logger.getLogger(MessageBean.class.getName());
    private static Level level = Level.INFO;

    public MessageBean() {
        logger.log(level, "MessageBean..");
    }

    public List<Message> getMessages() throws Exception {
        logger.log(level, "MessageBean.getMessages..");
        List<Message> messages = new ArrayList<Message>();
        messages = NNTP.getMessages();
        logger.log(level, "GOT MESSAGES AS SO..");
        logger.log(level, messages.toString());
        logger.log(level, "..GOT MESSAGES AS SO");
        return messages;
    }
}

现在，MessageBean调用实用程序NNTP类，该类与localhost上的leafnode进行交互，因此它在CLI中非常快。但是，对于facelets而言，显然不够快，因为我一直遇到套接字错误。

从日志记录到Glassfish，我看到leafnode正确地将文章返回到实用程序类，并且最终，MessageBean甚至有一个大的List。

问题似乎是，应该存在多个MessageBean实例。然而，他们并不是所有人都能够同时查询leafnode，大概是成功的。也许这是套接字错误的来源。

无论如何，我不想将javax.mail.Message持久存储到数据库中，leafnode已经将消息保留得很好。我严格要在localhost上与leafnode接口。

我需要一些可怕的枚举单身人士吗？这是我所知道的唯一“模式”，所以我认为它必须适用于这种情况。或者，是否有一些替代方法来减慢MessageBean，以确保它实际上从实用程序NNTP类获取其消息，然后将它们传递给facelet？或者，这种延迟会导致某种错误吗？

这里有什么好方法？我不打算构建一个功能齐全的NNTP客户端，只是摆弄了一个有一些延迟的leafnode。

-----------------------------------

解决方案：关闭套接字properly并使用容器类，如下面的setEntities：

package net.bounceme.dur.nntp;

import java.util.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.mail.*;

public enum SingletonNNTP {

    INSTANCE;
    private final Logger logger = Logger.getLogger(SingletonNNTP.class.getName());
    private final Level level = Level.INFO;
    private Properties props = new Properties();
    private List<Message> messages = new ArrayList<Message>();
    private boolean loaded = false;
    private List<MessageEntity> messageEntities = new ArrayList<MessageEntity>();

    private SingletonNNTP() {
        logger.logp(level, "SingletonNNTP", "SingletonNNTP", "only once...");
        props = PropertiesReader.getProps();
        if (!loaded) {
            try {
                loaded = setMessages();
            } catch (Exception ex) {
                Logger.getLogger(SingletonNNTP.class.getName()).log(Level.SEVERE, "FAILED TO LOAD MESSAGES", ex);
            }
        }
    }

    public List<Message> getMessages(boolean debug) throws Exception {
        logger.logp(level, "SingletonNNTP", "getMessages", "returning messages");
        return Collections.unmodifiableList(messages);
    }

    private boolean setMessages() throws Exception {
        logger.logp(level, "SingletonNNTP", "setMessages", "connecting to leafnode");
        Session session = Session.getDefaultInstance(props);
        session.setDebug(false);
        Store store = session.getStore(new URLName(props.getProperty("nntp.host")));
        store.connect();
        Folder root = store.getDefaultFolder();
        Folder folder = root.getFolder(props.getProperty("nntp.group"));
        folder.open(Folder.READ_ONLY);
        Message[] msgs = folder.getMessages();
        messages = Arrays.asList(msgs);
        setEntities();
        folder.close(false);
        store.close();
        return true;
    }

    public List<MessageEntity> getEntities() {
        logger.logp(level, "SingletonNNTP", "getEntities", "getting entities");
        for (MessageEntity m : messageEntities) {
            for (Header h : m.getHeaders()) {
                logger.log(level, h.toString());
            }
        }
        return Collections.unmodifiableList(messageEntities);
    }

    private void setEntities() throws Exception {
        logger.logp(level, "SingletonNNTP", "loadEntities", "trying to convert");
        messageEntities = new ArrayList<MessageEntity>();
        for (Message message : messages) {
            MessageEntity entity = new MessageEntity();
            Enumeration allHeaders = message.getAllHeaders();
            List<Header> headers = new ArrayList<Header>();
            while (allHeaders.hasMoreElements()) {
                Header hdr = (Header) allHeaders.nextElement();
                headers.add(hdr);
            }
            entity.setHeaders(headers);
            entity.setSubject(message.getSubject());
            entity.setContent(message.getContent().toString());
            entity.setSentDate(message.getReceivedDate());
            messageEntities.add(entity);
        }
    }
}

Answer 1

根据我对您的问题的理解，您实际上需要对NNTP.getMessages()进行同步并发访问。如果是这样，并且您在EJB上下文中使用托管bean，我相信Managing Concurrent Access in a Singleton Session Bean可以帮助您。如果没有直接帮助，我相信您可以利用ReentrantLock来测试对NNTP的并发控制是否可以解决问题。

@Named与localhost的bean同步

-----------------------------------

1 个答案: