Java 如何在启动前检查 JRE 版本？
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How to check JRE version prior to launch?
提问by Vladimir Prenner
What's the best way to determine if the version of the JRE installed on a machine is high enough for the application which the user wants to run? Is there a way of doing it using java-only stuff? I'd like the solution to work on Windows/Linux/MacOSX - if the JRE version is too low a message should be displayed. Currently I'm getting an exception if i try to run it on Java 1.5 (the app is built for Java 1.6). If there's no universal solution, what's the best way to do it on Windows?
确定机器上安装的 JRE 版本对于用户想要运行的应用程序是否足够高的最佳方法是什么？有没有办法使用纯java的东西来做到这一点？我希望该解决方案适用于 Windows/Linux/MacOSX - 如果 JRE 版本太低，则应显示一条消息。目前，如果我尝试在 Java 1.5 上运行它（该应用程序是为 Java 1.6 构建的），则会出现异常。如果没有通用的解决方案，那么在 Windows 上最好的方法是什么？
采纳答案by matt b
An application built for a higher-version JRE will not run on a lower-version JRE. So you wouldn't be able to just add code to your application to check the JRE version - if the JRE version was incompatible, your JRE-version-checking code would not run in the first place.
为较高版本的 JRE 构建的应用程序不会在较低版本的 JRE 上运行。因此，您无法仅向应用程序添加代码来检查 JRE 版本 - 如果 JRE 版本不兼容，您的 JRE 版本检查代码将不会首先运行。
What you'd have to do is have some sort of launcher application that is built for a lower-version JRE (1.3?) that checks the version and then launches your app if necessary. This sounds kind of kludgy to me.
您需要做的是拥有某种为低版本 JRE (1.3?) 构建的启动器应用程序，用于检查版本，然后在必要时启动您的应用程序。这对我来说听起来有点笨拙。
What about checking the version during installation? Are you installing the app in a way that allows you to check environment variables, or do any sort of scripting?
在安装过程中检查版本怎么样？您是否以允许您检查环境变量或执行任何类型的脚本的方式安装应用程序？
回答by Tanktalus
Generally, we've approached this with a C or (when unix-only) shell wrapper. Not sure this will really work for you.
通常，我们使用 C 或（仅在 Unix 时）shell 包装器来解决此问题。不确定这真的适合你。
We also approach this by embedding the JRE in our product. Takes care of 99.9% of the cases (the other 0.1% of the time is a user explicitly changing our configuration to use a different JVM). Again, not sure that this is a reasonable solution for you.
我们还通过在我们的产品中嵌入 JRE 来解决这个问题。处理 99.9% 的情况（另外 0.1% 的时间是用户明确更改我们的配置以使用不同的 JVM）。同样，不确定这对您来说是一个合理的解决方案。
In our case, there is significant amounts of native code (JNI and otherwise), so tailoring an installable image for each platform we support is required anyway. But if you're dealing with a pure-Java solution, you may simply have to document your minimum and tell people to get with the program (no pun intended) if they're to run your stuff. It's sorta like people complaining that my Mac won't run MSVC, or that my Linux box is having problems running World of Warcraft. That's just not the (virtual) machine the software is targeted for - you need to switch. At least in the Java world, we really can call this an upgrade, though, without hurting anyone's OS-religious feelings. (Try telling the Mac user to "upgrade" to Windows XP to run MSVC - there's a beat-down waiting to happen.)
在我们的例子中，有大量的本机代码（JNI 和其他），因此无论如何都需要为我们支持的每个平台定制一个可安装的映像。但是，如果您正在处理纯 Java 解决方案，您可能只需要记录您的最低要求，并告诉人们如果他们要运行您的东西，就使用该程序（无意双关语）。这有点像人们抱怨我的 Mac 无法运行 MSVC，或者我的 Linux 机器在运行魔兽世界时出现问题。这不是软件针对的（虚拟）机器——您需要切换。至少在 Java 世界中，我们确实可以称其为升级，但不会伤害任何人的操作系统宗教感情。（尝试告诉 Mac 用户“升级”到 Windows XP 以运行 MSVC - 等待发生的是一个击败。）
回答by Spencer Kormos
System.getProperties() gives you a listing of JVM properties including the different version ids of the JRE, JVM and specification. This implemented for all versions of Java so should work regardless of version compiled in and version run in, or the implementation.
System.getProperties() 为您提供 JVM 属性列表，包括 JRE、JVM 和规范的不同版本 ID。这适用于所有 Java 版本，因此无论编译版本和运行版本或实现如何，都应该可以工作。
If you write a basic class to test the version, you can call this first in your main() launching class. It must really be basic functionality though or you might risk breaking it.
如果您编写一个基本类来测试版本，您可以先在 main() 启动类中调用它。不过，它必须确实是基本功能，否则您可能会冒着破坏它的风险。
回答by Spencer Kormos
You might also consider using Commons-Launcher, which allows you to setup various environment settings, or perform pre-checks before calling your application.
您也可以考虑使用 Commons-Launcher，它允许您设置各种环境设置，或在调用应用程序之前执行预检查。
回答by jim
For the launcher - Check the version in there.
对于启动器 - 检查那里的版本。
Inside the APP; as above use System.getProperties();
APP内；如上所述使用 System.getProperties();
Properties sProp = java.lang.System.getProperties();
String sVersion = sProp.getProperty("java.version");
sVersion = sVersion.substring(0, 3);
Float f = Float.valueOf(sVersion);
if (f.floatValue() < (float) 1.4) {
System.out.println("Java version too low ....");
System.exit(1);
}
...
回答by TREE
You could do this using reflection and two compilers. Compile a main class with the oldest java version you want to be able to run at all with. It checks the version using System.getProperty("java.version"), or whatever, and then uses reflection to load your realmain class if that check passes, possibly even loading the jar directly. The JRE shouldn't load any classes that weren't referenced by your outer main class at compile time.
您可以使用反射和两个编译器来做到这一点。使用您希望能够运行的最旧 Java 版本编译主类。它使用System.getProperty("java.version")或其他方式检查版本，然后如果检查通过，则使用反射加载真正的主类，甚至可能直接加载 jar。JRE 不应加载任何在编译时未被外部主类引用的类。
回答by TREE
Hmm .. call me a boring guy, but what's wrong with using Launch4J or any other native launcher, for instance.
嗯.. 叫我一个无聊的人，但是使用 Launch4J 或任何其他本地启动器有什么问题，例如。
Use a native launcher to check the JVM version before actually running your code. Java only solutions (in my book) only make sense when you deal with developers; once you hit end-users, you'll realize that they dont care about Java or its technical details at all. If you would have written your application in GW-Basic they would not care less as long as your application works.
在实际运行代码之前，使用本机启动器检查 JVM 版本。仅 Java 的解决方案（在我的书中）只有在与开发人员打交道时才有意义；一旦你接触到最终用户，你就会意识到他们根本不关心 Java 或其技术细节。如果您使用 GW-Basic 编写您的应用程序，只要您的应用程序正常工作，他们就不会在意。
If Java 1.6 is not installed, lauchner4j will point the user to the download page for JDK 1.6. Thats probably more suitable for your problem than doing magic in Java.
如果未安装 Java 1.6，lauchner4j 会将用户指向 JDK 1.6 的下载页面。这可能比在 Java 中做魔术更适合您的问题。
回答by Mnementh
You might consider Java Webstart. Even if the name implies something like applets, it's about standalone-applications. Webstart is a launcher, that checks a JNLP-file (a simple XML-file, where you configure the download-location of your app, the needed Java-version and some other metadata) and starts your app with the correct JRE. It even updates the application, if a newer version is available. The downside is, you have to write a JNLP-file. Here is an example:
您可以考虑Java Webstart。即使这个名字暗示了小程序之类的东西，它也是关于独立应用程序的。Webstart 是一个启动器，它检查 JNLP 文件（一个简单的 XML 文件，您可以在其中配置应用程序的下载位置、所需的 Java 版本和一些其他元数据）并使用正确的 JRE 启动您的应用程序。如果有更新的版本可用，它甚至会更新应用程序。缺点是，您必须编写 JNLP 文件。下面是一个例子：
<?xml version="1.0" encoding="utf-8"?>
<!--
###############################################################################
#
# @(#)draw.jnlp 1.6 02/09/11
#
# JNLP File for Draw Demo Application
#
###############################################################################
-->
<jnlp spec="0.2 1.0"
codebase="http://java.sun.com/javase/technologies/desktop/javawebstart/apps"
href="draw.jnlp">
<information>
<title>Draw 4 App</title>
<vendor>Sun Microsystems, Inc.</vendor>
<homepage href="http://java.sun.com/javase/technologies/desktop/javawebstart/demos.html"/>
<description>A minimalist drawing application along the lines of Illustrator</description>
<description kind="short">Draw Demo Short Description</description>
<icon href="images/draw.jpg"/>
<offline-allowed/>
</information>
<resources>
<j2se version="1.3+" href="http://java.sun.com/products/autodl/j2se"/>
<j2se version="1.3+"/>
<jar href="draw.jar" main="true" download="eager"/>
</resources>
<application-desc main-class="Draw"/>
</jnlp>
A second possibility is to use a launcher-program. An example is the Apache Commons Launcher. You can also write some launcher app yourself, but that's usually not worth the effort.
第二种可能性是使用启动程序。一个例子是Apache Commons Launcher。您也可以自己编写一些启动器应用程序，但这通常是不值得的。
回答by Peter Smith
I find that WinRun4Jworks quite well for me (but then again I may be biased since I wrote it:-)). This lets you specify a minimum and/or maximum version of java allowed. It will pop up a message box to the user if a suitable JRE version is not found (and the message is customisable).
我发现WinRun4J对我来说效果很好（但是我可能会因为我写它而有偏见:-)）。这使您可以指定允许的最低和/或最高 Java 版本。如果没有找到合适的 JRE 版本（并且该消息是可定制的），它将向用户弹出一个消息框。
回答by lucrussell
You can require a Java version when running the Java command, e.g. java -version:1.6* com.me.MyClass. Not sure if this works on all releases of Java, but it works OK on 1.6 anyway.
运行 Java 命令时，您可能需要 Java 版本，例如java -version:1.6* com.me.MyClass. 不确定这是否适用于所有 Java 版本，但无论如何它在 1.6 上都可以正常工作。
