blocks|key|605430|text|最好的页面是这个：http://www.oracle.com/technetwork/java/restrictions-142267.html|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|605431|它详细介绍了对Java编程模型的限制。|605432|除了上面提到的安全性、可移植性、集群、线程处理之外，线程还考虑事务和错误处理(文件系统不是事务性的)。|605433|然而，JVM中没有黑魔法，您可以创建文件(只要您有相应的权限)，使用静态变量，如果您知道自己在做什么，就可以创建线程。|605434|最好花点时间来理解为什么这些限制通常是建议的，而不是为了兼容而跳转编写JCA连接器。|605435|entityMap|0|LINK|mutability|MUTABLE|url|http://www.oracle.com/technetwork/java/restrictions-142267.html^0|9|1R|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|6|7|X|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Y|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|Z|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|10|8|@]|9|@]|C|$]]|$1|L|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|M|$N|$5|O|P|Q|C|$R|S]]]]

The best page to look at is this one: <a href="http://www.oracle.com/technetwork/java/restrictions-142267.html" rel="nofollow noreferrer">http://www.oracle.com/technetwork/java/restrictions-142267.html</a>

It covers in detail the restrictions over the Java EE programming model.

Apart from the point mentionned above Security, Portability, Clustering, Threading also consider transactions and error handling (File systems are not transactional).

There is however no black magic happening in the JVM and you can create files (as long as you have the corresponding rights), use static variables, and create threads if you know what you're doing.

Better take the time to understand why these restriction are usually suggested, than to jump and write a JCA connector for the sake of being compliant.

blocks|key|1260949|text|您应该在Java容器本身中做任何事情:您无法确定您将对文件系统有任何一致的访问。造成这种情况的原因有很多，最明显的原因是在容器中运行的应用程序将具有：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1260950|1260951|无法确定以后对EJB的任何调用甚至都在同一个物理服务器上，该服务器可以访问相同的文件/文件系统(例如，集群)、|unordered-list-item|1260952|、没有可能相互干扰(多个应用程序试图写入同一个文件)、|1260953|没有安全问题(一个应用程序可以读取机密数据)|1260954|1260955|你也应该假设你不应该|offset|length|style|BOLD|1260956|1260957|创建您自己的线程(容器将管理您自己的线程；如果您创建自己的线程，您可能会在CPU时间的容器中饥饿其他应用程序)|1260958|使用socket-IO+(也有安全问题)|1260959|。|1260960|entityMap^0|0|0|0|0|0|0|6|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|10|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|11|8|@]|9|@]|A|$]]|$1|F|3|G|5|E|7|12|8|@]|9|@]|A|$]]|$1|H|3|I|5|E|7|13|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|15|8|@$M|16|N|17|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|18|8|@]|9|@]|A|$]]|$1|R|3|S|5|E|7|19|8|@]|9|@]|A|$]]|$1|T|3|U|5|E|7|1A|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|1B|8|@]|9|@]|A|$]]|$1|X|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|Y|$]]

You should do everything within the Java EE container itself: you can have no certainty that you will have any consistent access to the filesystem. There are many reasons for this, the most obvious being that applications running within a container will have:

<ul>
<li>no certainty that any subsequent invocation of an EJB would even be on the same physical server with access to the same files/filesystem (e.g. upon clustering)</li>
<li>no possibility of interfering with each other (multiple applications attempting to write to the same file)</li>
<li>no security issues (one app writing confidential data which another app could read)</li>
</ul>

You should also assume that you shouldn't:

<ul>
<li>create your own threads (the container will manage this for you; if you create your own you may starve other applications in the container of CPU time)</li>
<li>use socket-IO (also has security issues)</li>
</ul>

blocks|key|1260985|text|即使您可以访问文件系统，对于分布式系统，您也不能确定下次调用方法时，它将在写入文件的同一台机器上处理。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1260986|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Even if you have access to the filesystem, with distributed systems you can't be sure that the next time a method is called, it will be handled on the same machine where the file was written.

blocks|key|1293769|text|根据Java规范，EJB被严格禁止通过“资源管理器”(JDBC、JNDI、JCA等)以外的任何其他方式访问任何外部资源，其中特别包括通过java.io包的类访问本地文件系统。此外，ClassLoader也不能用于这种访问，例如从应用程序的类路径加载属性文件。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1293770|其他答覆亦已说明原因：|1293771|issues|1293772|Portability+issues|unordered-list-item|1293773|
|1293774|Clustering+issues|1293775|1293776|Threading发布|1293777|1293778|最终，解决这些问题的最佳资源是一个数据库。|1293779|entityMap^0|1W|7|2I|B|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|15|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|16|8|@]|D|@]|E|$]]|$1|O|3|P|5|L|7|17|8|@]|D|@]|E|$]]|$1|Q|3|N|5|6|7|18|8|@]|D|@]|E|$]]|$1|R|3|S|5|L|7|19|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]|$1|U|3|V|5|6|7|1B|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|X|$]]

Per Java EE specifications, EJBs are strictly prohibited from accessing any external resources by any means other than through a "resource manager" (JDBC, JNDI, JCA, etc) and this includes especially access to the local file system through classes of the <code>java.io</code> package. Additionally, nor can a <code>ClassLoader</code> be used for such access, such as to load a properties file from the application's classpath.

Reasons for this have already been given in other answers:

<ul>
<li>Security issues</li>
<li>Portability issues</li>
<li>Clustering issues</li>
<li>Threading issues</li>
</ul>

Ultimately, the best resource for these matters is a database.

blocks|key|605381|text|如果您的实例不是集群的，或者可以保证所有实例都可以使用网络驱动器，那么使用files来读取/写入文件并不是真正的问题。然而，必须注意找到正确的道路，并酌情清理。通常，没有任何真正的需要写文件，所以再想一想。大多数人给出的主要原因是，在集群中，不同的服务器不会看到相同的文件，导致路径改变等等。最后，大多数小型应用程序没有在这样的集群中运行.|type|unstyled|depth|inlineStyleRanges|entityRanges|data|605382|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If your instance is not clustered or one can guarantee that all instances can use a network drive then its not really a problem to use the File apis to read/write files. However care must be taken to get paths right and clean up as appropriate. Often there are not any real needs to write files so think about it again. The main reason most people give is that in a cluster different servers wont see the same file bcause paths change and so on. In the end most many small apps dont run in such a cluster...

blocks|key|1261123|text|您应该将文件系统视为企业信息系统(EIS)。然后，您可以创建一个访问此EIS的ResourceAdapter，类似于访问数据库的JDBC适配器。规范在这里：http://java.sun.com/j2ee/connector/download.html。这意味着文件访问是可能的，但要复杂得多。这个规范甚至允许您创建某种称为Work的“线程”。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1261124|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/j2ee/connector/download.html^0|26|1C|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You should consider a Filesystem as a Enterprise Information System (EIS). Then you can create a ResourceAdapter which accesses this EIS, similar to a JDBC adapter which accesses a database. The spec is here: <a href="http://java.sun.com/j2ee/connector/download.html" rel="nofollow noreferrer">http://java.sun.com/j2ee/connector/download.html</a> . This means file access is possible, but much more complicated. This spec even allows you to create some sort of "threads" called Work.

blocks|key|1293744|text|因为Java规范没有提供用于编写文件的API。当然，您可以使用普通的Java来创建文件，但是您必须确保这段代码是线程安全的，必须有人清理文件，文件名被传递到下一个bean，文件在您的bean被移动到集群中的另一个节点时被迁移，等等。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1293745|因此，虽然您可以这样做，但在实践中，您将遇到许多小问题，这使得在Java中处理文件变得非常困难。|1293746|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Because the Java EE spec doesn't offer an API to write files. Of course, you can just use the normal Java IO API to create files but you must make sure that this code is thread safe, that someone cleans up the files, that the file name is passed on to the next bean, that the file is migrated when your bean is moved to another node in the cluster, etc.

So while you can do it, in practice, you'll encounter lots of small problems which make handling files in Java EE really hard.

blocks|key|1293830|text|为了与遗留的非j2ee系统进行互操作，您有时不得不做一些“不好的事情”，如socket+i/o、写入文件等。在最好的情况下，j2ee规范将被严格遵守，但为了方便起见和完成工作，人们总是可以不使用J2EE的东西。有一些方法可以安全地和深思熟虑地完成这些事情。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1293831|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

In order to inter-operate with a legacy non-j2ee systems, you occasionally have to do "bad things" like socket i/o, writing to files, etc. In the best of all worlds the j2ee spec would be followed strictly, but people get away with non-j2ee stuff all the time for the sake of expediency and getting the job done. There are ways to pull these things off safely and thoughtfully.

Today one person told to me that "Java EE programmers do not write to files". Why can I not write to files from within a Java EE container (for example from JBoss)? What is wrong?

Java EE programmers do not write to files 

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

教程

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云智能顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云AI代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

功能1上新10个字符

功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符功能2描述100个字符。

功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符功能2上新100个字符。

功能5描述100个字符功能5描述100个字符功能5描述100个字符功能5描述100个字符功能5描述100个字符功能5描述100个字符

功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符功能5上新100个字符

功能4上新

文章&问答评论现已支持表情

全新交互，全新视觉，新增快捷键、悬浮工具栏、高亮块等功能并同时优化现有功能，全面提升创作效率和体验

社区富文本编辑器全新改版！诚邀体验～ 

精选全网热门MCP server，让你的AI更好用 🚀

💥开发者 MCP广场重磅上线！

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

聚焦“写作效率、视觉美观与运行性能”三方面进行全面升级，为您提供更高效、稳定的创作环境

社区富文本&Markdown编辑器全新改版上线，欢迎大家体验!

诚挚邀请您参与本次调研，分享您的真实使用感受与建议。您的反馈至关重要，感谢您的支持与参与！

社区新版编辑器体验调研

今天，一个人对我说："Java程序员不写文件“。为什么我不能从Java容器(例如从JBoss)中写入文件？怎么啦？

问Java程序员不向文件写入
EN

回答 8

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Java程序员不向文件写入EN

回答 8

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Java程序员不向文件写入
EN