blocks|key|352992|text|(更新:如果我可以删除这个答案，我会的，尽管因为它被接受了，所以我不能。我正在更新描述，以提供更好的指导，并阻止人们使用我在原始答案中概述的糟糕的实践)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|352993|您可以通过上下文或环境参数指定这些参数，例如在context.xml中。请参阅此页上标题为"Context+Parameters“和"Environment+Entries”的部分：|352994|http://tomcat.apache.org/tomcat-5.5-doc/config/context.html|offset|length|352995|正如@netjeff指出的那样，这些值将通过Context.lookup(String)方法可用，而不是作为系统参数。|352996|指定这些值的另一种方法是在要部署的web应用程序的web.xml文件中定义变量(见下文)。正如@Roberto+Lo+Giacco指出的那样，这通常被认为是一种糟糕的实践，因为部署的工件不应该是特定于环境的。但是，如果您真的想这样做，下面是配置代码片段：|352997|<env-entry>
++++<env-entry-name>SMTP_PASSWORD</env-entry-name>
++++<env-entry-type>java.lang.String</env-entry-type>
++++<env-entry-value>abc123ftw</env-entry-value>
</env-entry>|code-block|syntax|javascript|352998|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|1N|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Z|8|@]|9|@$F|10|G|11|1|12]]|A|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|14|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|15|8|@]|9|@]|A|$O|P]]|$1|Q|3|-4|5|6|7|16|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|E]]]]

(Update: If I could delete this answer I would, although since it's accepted, I can't. I'm updating the description to provide better guidance and discourage folks from using the poor practice I outlined in the original answer).

You can specify these parameters via context or environment parameters, such as in context.xml. See the sections titled "Context Parameters" and "Environment Entries" on this page:

<a href="http://tomcat.apache.org/tomcat-5.5-doc/config/context.html" rel="noreferrer">http://tomcat.apache.org/tomcat-5.5-doc/config/context.html</a>

As @netjeff points out, these values will be available via the Context.lookup(String) method and not as System parameters.

Another way to do specify these values is to define variables inside of the web.xml file of the web application you're deploying (see below). As @Roberto Lo Giacco points out, this is generally considered a poor practice since a deployed artifact should not be environment specific. However, below is the configuration snippet if you really want to do this:

<pre class="lang-xml prettyprint-override"><code>&lt;env-entry&gt;
 &lt;env-entry-name&gt;SMTP_PASSWORD&lt;/env-entry-name&gt;
 &lt;env-entry-type&gt;java.lang.String&lt;/env-entry-type&gt;
 &lt;env-entry-value&gt;abc123ftw&lt;/env-entry-value&gt;
&lt;/env-entry&gt;
</code></pre>

blocks|key|3350957|text|一般来说，你不应该依赖系统属性来配置webapp+--它们可以用来配置容器(例如Tomcat)，但不能用来配置运行在tomcat中的应用程序。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3350958|cliff.meyers已经提到了你应该在你的way应用中使用的方式。这是标准的方式，也适合您通过context.xml或server.xml方式进行配置的问题。|3350959|也就是说，如果您确实需要tomcat中的系统属性或其他jvm选项(如最大内存设置)，则应该创建一个名为"bin/setenv.sh“或"bin/setenv.bat”的文件。这些文件不存在于您下载的标准归档中，但如果它们存在，则在启动期间执行内容(如果您通过启动.sh/启动p.bat启动tomcat+)。这是将您自己的设置与标准tomcat设置分开的一种很好的方式，并使更新变得更容易。不需要调整startup.sh或catalina.sh。|3350960|(如果您将tomcat作为windows服务执行，则通常使用tomcat5w.exe、tomcat6w.exe等来配置该服务的注册表设置。)|3350961|编辑:另外，另一种可能性是使用JNDI+Resources。|offset|length|3350962|entityMap|0|LINK|mutability|MUTABLE|url|http://tomcat.apache.org/tomcat-5.5-doc/jndi-resources-howto.html^0|0|0|0|0|F|E|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|W|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@$J|Y|K|Z|1|10]]|A|$]]|$1|L|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|M|$N|$5|O|P|Q|A|$R|S]]]]

Generally you shouldn't rely on system properties to configure a webapp - they may be used to configure the container (e.g. Tomcat) but not an application running inside tomcat.

cliff.meyers has already mentioned the way you should rather use for your webapplication. That's the standard way, that also fits your question of being configurable through context.xml or server.xml means.

That said, should you really need system properties or other jvm options (like max memory settings) in tomcat, you should create a file named "bin/setenv.sh" or "bin/setenv.bat". These files do not exist in the standard archive that you download, but if they are present, the content is executed during startup (if you start tomcat via startup.sh/startup.bat). This is a nice way to separate your own settings from the standard tomcat settings and makes updates so much easier. No need to tweak startup.sh or catalina.sh.

(If you execute tomcat as windows servive, you usually use tomcat5w.exe, tomcat6w.exe etc. to configure the registry settings for the service.)

EDIT: Also, another possibility is to go for <a href="http://tomcat.apache.org/tomcat-5.5-doc/jndi-resources-howto.html" rel="noreferrer">JNDI Resources</a>.

blocks|key|3351029|text|在只使用System.getProperty()的情况下，cliff.meyer最初的回答建议使用<env-entry>不会有什么帮助。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3351030|根据Tomcat6.0docs++is+for+JNDI。所以这意味着它不会对System.getProperty()产生任何影响。|3351031|使用cliff.meyer示例中的<env-entry>，下面的代码|3351032|System.getProperty("SMTP_PASSWORD");|code-block|syntax|javascript|3351033|将返回null，而不是值"abc123ftw“。|3351034|根据Tomcat6文档，要使用<env-entry>，必须编写如下代码才能使用<env-entry>|3351035|//+Obtain+our+environment+naming+context
Context+initCtx+=+new+InitialContext();
Context+envCtx+=+(Context)+initCtx.lookup("java:comp/env");

//+Look+up+our+data+source
String+s+=+(String)envCtx.lookup("SMTP_PASSWORD");|3351036|注意:我还没有实际尝试过上面的例子。但是我用System.getProperty()尝试过<env-entry>，这肯定不起作用。|3351037|entityMap|0|LINK|mutability|MUTABLE|url|http://tomcat.apache.org/tomcat-6.0-doc/jndi-resources-howto.html^0|1D|B|0|13|K|G|C|0|0|H|B|0|0|0|F|B|13|B|0|0|19|B|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|H|3|I|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1G|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1H|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1I|8|@$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]]|D|@]|E|$]]|$1|S|3|T|5|L|7|1N|8|@]|D|@]|E|$M|N]]|$1|U|3|V|5|6|7|1O|8|@$9|1P|A|1Q|B|C]]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1R|8|@]|D|@]|E|$]]]|X|$Y|$5|Z|10|11|E|$12|13]]]]

cliff.meyers's original answer that suggested using <code>&lt;env-entry&gt;</code> will not help when using only System.getProperty() 

According to the Tomcat 6.0 docs <a href="http://tomcat.apache.org/tomcat-6.0-doc/jndi-resources-howto.html" rel="nofollow noreferrer"><code>&lt;env-entry&gt;</code> is for JNDI</a>. So that means it won't have any effect on <code>System.getProperty()</code>.

With the <code>&lt;env-entry&gt;</code> from cliff.meyers's example, the following code 

<pre class="lang-java prettyprint-override"><code>System.getProperty("SMTP_PASSWORD");
</code></pre>

will return null, not the value "abc123ftw".

According to the Tomcat 6 docs, to use <code>&lt;env-entry&gt;</code> you'd have to write code like this to use <code>&lt;env-entry&gt;</code>:

<pre class="lang-java prettyprint-override"><code>// Obtain our environment naming context
Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");

// Look up our data source
String s = (String)envCtx.lookup("SMTP_PASSWORD");
</code></pre>

Caveat: I have not actually tried the example above. But I have tried <code>&lt;env-entry&gt;</code> with System.getProperty(), and that definitely does not work.

blocks|key|3351051|text|也可以让ServletContextListener设置系统属性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3351052|import+java.util.Enumeration;
import+javax.servlet.*;

public+class+SystemPropertiesHelper+implements
++++++++javax.servlet.ServletContextListener+{
++++private+ServletContext+context+=+null;

++++public+void+contextInitialized(ServletContextEvent+event)+{
++++++++context+=+event.getServletContext();
++++++++Enumeration<String>+params+=+context.getInitParameterNames();

++++++++while+(params.hasMoreElements())+{
++++++++++String+param+=+(String)+params.nextElement();
++++++++++String+value+=+
++++++++++++context.getInitParameter(param);
++++++++++if+(param.startsWith("customPrefix."))+{
++++++++++++++System.setProperty(param,+value);
++++++++++}
++++++++}
++++}

++++public+void+contextDestroyed(ServletContextEvent+event)+{
++++}
}|code-block|syntax|javascript|3351053|然后把它放到你的web.xml中(对于context.xml也应该是可行的)|3351054|<context-param>
++++++++<param-name>customPrefix.property</param-name>
++++++++<param-value>value</param-value>
++++++++<param-type>java.lang.String</param-type>
</context-param>

<listener>
++++<listener-class>servletUtils.SystemPropertiesHelper</listener-class>++++
</listener>|3351055|这对我很管用。|3351056|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

It's also possible letting a ServletContextListener set the System properties:

<pre class="lang-java prettyprint-override"><code>import java.util.Enumeration;
import javax.servlet.*;

public class SystemPropertiesHelper implements
 javax.servlet.ServletContextListener {
 private ServletContext context = null;

 public void contextInitialized(ServletContextEvent event) {
 context = event.getServletContext();
 Enumeration&lt;String&gt; params = context.getInitParameterNames();

 while (params.hasMoreElements()) {
 String param = (String) params.nextElement();
 String value = 
 context.getInitParameter(param);
 if (param.startsWith("customPrefix.")) {
 System.setProperty(param, value);
 }
 }
 }

 public void contextDestroyed(ServletContextEvent event) {
 }
}
</code></pre>

And then put this into your web.xml (should be possible for context.xml too)

<pre class="lang-xml prettyprint-override"><code>&lt;context-param&gt;
 &lt;param-name&gt;customPrefix.property&lt;/param-name&gt;
 &lt;param-value&gt;value&lt;/param-value&gt;
 &lt;param-type&gt;java.lang.String&lt;/param-type&gt;
&lt;/context-param&gt;

&lt;listener&gt;
 &lt;listener-class&gt;servletUtils.SystemPropertiesHelper&lt;/listener-class&gt; 
&lt;/listener&gt;
</code></pre>

It worked for me.

blocks|key|353093|text|在tomcat配置上设置系统属性的另一种方法是使用CATALINA_OPTS环境变量|type|unstyled|depth|inlineStyleRanges|entityRanges|data|353094|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|$]]

An alternative to setting the system property on tomcat configuration is to use CATALINA_OPTS environment variable

blocks|key|3138337|text|这个问题在Apache+wiki中得到了解决。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3138338|问：“我能为每个set应用程序设置不同的Java系统属性吗？”|3138339|答案是:不。如果您可以编辑Tomcat的启动脚本(或者最好是创建一个setenv.sh文件)，那么您可以向-D添加“Java”选项。但在Java中，同一JVM中的不同类不能有不同的系统属性值。还有一些其他可用的方法，比如使用ServletContext.getContextPath()来获取web应用程序的上下文名称并相应地定位一些资源，或者在web应用程序的WEB-INF/web.xml文件中定义元素，然后在Tomcat上下文文件(META-INF/context.xml)中设置它们的值。参见http://tomcat.apache.org/tomcat-7.0-doc/config/context.html。|offset|length|3138340|http://wiki.apache.org/tomcat/HowTo#Can_I_set_Java_system_properties_differently_for_each_webapp.3F|3138341|entityMap|0|LINK|mutability|MUTABLE|url|http://tomcat.apache.org/tomcat-7.0-doc/config/context.html|1^0|0|0|6Y|1N|0|0|0|2R|1|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@]|9|@$F|V|G|W|1|X]]|A|$]]|$1|H|3|I|5|6|7|Y|8|@]|9|@$F|Z|G|10|1|11]]|A|$]]|$1|J|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]|R|$5|M|N|O|A|$P|I]]]]

This question is addressed in the Apache wiki.

Question: "Can I set Java system properties differently for each webapp?"

Answer: No. If you can edit Tomcat's startup scripts (or better create a setenv.sh file), you can add "-D" options to Java. But there is no way in Java to have different values of system properties for different classes in the same JVM. There are some other methods available, like using ServletContext.getContextPath() to get the context name of your web application and locate some resources accordingly, or to define elements in WEB-INF/web.xml file of your web application and then set the values for them in Tomcat context file (META-INF/context.xml). See <a href="http://tomcat.apache.org/tomcat-7.0-doc/config/context.html" rel="noreferrer">http://tomcat.apache.org/tomcat-7.0-doc/config/context.html</a> . 

<a href="http://wiki.apache.org/tomcat/HowTo#Can_I_set_Java_system_properties_differently_for_each_webapp.3F" rel="noreferrer">http://wiki.apache.org/tomcat/HowTo#Can_I_set_Java_system_properties_differently_for_each_webapp.3F</a>

blocks|key|3351195|text|您可以向<tomcat+installation+directory>/conf目录中的catalina.properties文件添加必要的属性。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3351196|参考：https://tomcat.apache.org/tomcat-8.0-doc/config/index.html|3351197|3351198|所有系统属性都可用，包括使用-D语法设置的属性、由JVM自动提供的属性以及在$CATALINA_BASE/conf/catalina.properties文件中配置的属性。|blockquote|3351199|3351200|entityMap|0|LINK|mutability|MUTABLE|url|https://tomcat.apache.org/tomcat-8.0-doc/config/index.html^0|4|10|18|J|0|3|1M|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@$9|10|A|11|1|12]]|E|$]]|$1|H|3|-4|5|6|7|13|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|14|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|15|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

You could add necessary properties to <code>catalina.properties</code> file in <code>&lt;tomcat installation directory&gt;/conf</code> directory.

Reference: <a href="https://tomcat.apache.org/tomcat-8.0-doc/config/index.html" rel="nofollow noreferrer">https://tomcat.apache.org/tomcat-8.0-doc/config/index.html</a>

<blockquote>
 All system properties are available including those set using the -D
 syntax, those automatically made available by the JVM and those
 configured in the $CATALINA_BASE/conf/catalina.properties file.
</blockquote>

blocks|key|3138414|text|如果您希望根据文档在上下文中定义环境变量，则应按如下方式定义它们|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3138415|<Context+...>
++...
++<Environment+name="maxExemptions"+value="10"
+++++++++type="java.lang.Integer"+override="false"/>
++...
</Context>|code-block|syntax|javascript|3138416|还可以按如下方式使用它们：|3138417|((Context)new+InitialContext().lookup("java:comp/env")).lookup("maxExemptions")|3138418|您应该将10作为输出。|offset|length|style|CODE|3138419|entityMap^0|0|0|0|0|4|2|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

If you want to define an environment variable in your context base on documentation you shod define them as below 

<pre><code>&lt;Context ...&gt;
 ...
 &lt;Environment name="maxExemptions" value="10"
 type="java.lang.Integer" override="false"/&gt;
 ...
&lt;/Context&gt;
</code></pre>

Also use them as below: 

<pre><code>((Context)new InitialContext().lookup("java:comp/env")).lookup("maxExemptions")
</code></pre>

You should get <code>10</code> as output.

I understand that I can specify system properties to Tomcat by passing arguments with the -D parameter, for example "-Dmy.prop=value".

I am wondering if there is a cleaner way of doing this by specifying the property values in the context.xml file or some other tomcat configuration file. I would like to do this because, first, it is easier to keep track of my properties, and second, I have multiple contexts running and I don't know how I would specify context-specific properties through the -D parameter.

I am using Tomcat version 5.5.

How can I specify system properties in Tomcat configuration on startup?

容器

Java

我知道我可以通过将参数与"-Dmy.prop=value".一起传递给-D参数来指定Tomcat的系统属性我想知道是否可以通过在context.xml文件或其他tomcat配置文件中指定属性值来实现这一点。我之所以这样做是因为，首先，这样更容易跟踪我的属性，其次，我有多个上下文在运行，我不知道如何通过-D参数指定上下文...

问如何在启动时在Tomcat配置中指定系统属性？
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