Java 为什么Tomcat在使用共享库时启动速度会慢得多？

问题

我们有一个

tomcat7.0.35

运行在25个webapp上，这些webapp都共享相同版本的相同库（保证这一点永远不会改变！）。我想不是每个项目都加载同一个库，而是将它们移动到

${catalina.home}/lib

，这样可以减少所需的内存负载

然而，这是有代价的：每个webapp的部署时间从5秒增加到2分钟，这是不可行的

我做了一些阅读（例如），不幸的是，我无法找到减少启动时间的方法。有没有办法解决这个问题

请求的分析信息

我在两个不同的场景中运行了

jstack

和

jvisualvm

，我将在这里介绍一些发现（如果您需要其他信息，请告诉我）：

每个项目特定的库似乎都加载了：

org.apache.catalina.loader.WebappClassLoader.findResourceInternal

运行该方法的线程的jstack输出：

"localhost-startStop-1" daemon prio=10 tid=0x00007f17f8001800 nid=0x13b8 runnable [0x00007f183c800000]
   java.lang.Thread.State: RUNNABLE
        at java.text.MessageFormat.subformat(MessageFormat.java:1250)
        at java.text.MessageFormat.format(MessageFormat.java:819)
        at org.apache.naming.StringManager.getString(StringManager.java:145)
        at org.apache.naming.resources.BaseDirContext.lookup(BaseDirContext.java:500)
        at org.apache.naming.resources.ProxyDirContext.lookup(ProxyDirContext.java:310)
        at org.apache.catalina.loader.WebappClassLoader.findResourceInternal(WebappClassLoader.java:3011)
        at org.apache.catalina.loader.WebappClassLoader.findResource(WebappClassLoader.java:1262)
        at org.apache.catalina.loader.WebappClassLoader.getResourceAsStream(WebappClassLoader.java:1499)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2302)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2294)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2308)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2291)
        at org.apache.catalina.startup.ContextConfig.checkHandlesTypes(ContextConfig.java:2197)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2154)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:2034)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1990)
        at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1976)
        at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1326)
        at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:882)
        - locked <0x00000007f52f3ec0> (a org.apache.catalina.startup.ContextConfig)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:379)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5343)
        - locked <0x00000007f52f3bb8> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
        - locked <0x00000007f52f3bb8> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:902)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:879)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:636)
        at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1236)
        at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1877)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
        - <0x00000007846dfc70> (a java.util.concurrent.ThreadPoolExecutor$Worker)

"localhost-startStop-1" daemon prio=10 tid=0x00007f6280001000 nid=0x6ba3 runnable [0x00007f62c4950000]
   java.lang.Thread.State: RUNNABLE
        at java.lang.String.intern(Native Method)
        at java.util.jar.Attributes$Name.<init>(Attributes.java:466)
        at java.util.jar.Attributes.putValue(Attributes.java:168)
        at java.util.jar.Attributes.read(Attributes.java:421)
        at java.util.jar.Manifest.read(Manifest.java:251)
        at sun.security.util.SignatureFileVerifier.processImpl(SignatureFileVerifier.java:252)
        at sun.security.util.SignatureFileVerifier.process(SignatureFileVerifier.java:239)
        at java.util.jar.JarVerifier.processEntry(JarVerifier.java:307)
        at java.util.jar.JarVerifier.update(JarVerifier.java:218)
        at java.util.jar.JarFile.initializeVerifier(JarFile.java:345)
        at java.util.jar.JarFile.getInputStream(JarFile.java:412)
        - locked <0x00000007e8e9d890> (a sun.net.www.protocol.jar.URLJarFile)
        at sun.net.www.protocol.jar.JarURLConnection.getInputStream(JarURLConnection.java:162)
        at java.net.URLClassLoader.getResourceAsStream(URLClassLoader.java:233)
        at org.apache.catalina.loader.WebappClassLoader.getResourceAsStream(WebappClassLoader.java:1528)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2302)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2294)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2308)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2294)
        at org.apache.catalina.startup.ContextConfig.checkHandlesTypes(ContextConfig.java:2197)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2154)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:2034)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1990)
        at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1976)
        at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1326)
        at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:882)
        - locked <0x00000007858db6e0> (a org.apache.catalina.startup.ContextConfig)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:379)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:118)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:91)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5346)
        - locked <0x00000007858db318> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
        - locked <0x00000007858db318> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:902)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:879)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:636)
        at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1236)
        at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1877)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
        - <0x000000078460e618> (a java.util.concurrent.ThreadPoolExecutor$Worker)

---

WebappClassLoader首先搜索自己的类路径。因此，对于不在本地类路径中的每个类，都将查看所有jar文件。只有这样，它才会查看公共类加载器的委托

假设查看所有war的JAR需要x个时间量，而JAR的父类加载器需要y个时间量

平均来说，从正确的类加载器加载一个类将花费扫描它们所需时间的一半

从WebappClassLoader加载类将花费x/2的时间

从父类加载器加载类需要x+y/2

根据x和y，您可以更改类装入器的使用顺序。 如果y大于x，您应该保持默认设置，如果x大于，您可以尝试反转查找顺序。如果这样做，则从通用类加载器加载类将花费y/2时间，但从WebappClassLoader加载类将花费y+x/2时间

WebAppClassLoader对此设置有一个委托属性，如果将其设置为true，则可以实现此目的。

---

简而言之，请参见

conf/catalina.properties

shared.loader=shared/*.jar

换言之：

# List of comma-separated paths defining the contents of the "shared"
# classloader. Prefixes should be used to define what is the repository type.
# Path may be relative to the CATALINA_BASE path or absolute. If left as blank,
# the "common" loader will be used as Catalina's "shared" loader.
# Examples:
#     "foo": Add this folder as a class repository
#     "foo/*.jar": Add all the JARs of the specified folder as class
#                  repositories
#     "foo/bar.jar": Add bar.jar as a class repository
# Please note that for single jars, e.g. bar.jar, you need the URL form
# starting with file:.
shared.loader=shared/*.jar

默认情况下，Tomcat6+具有层次结构

与5.5中的默认值进行比较

---

因此，通过启用共享位置（该位置将只包含您的JAR），并与Tomcat lib文件夹（该文件夹已经有21个JAR）分开，您至少可以获得更清晰的JAR视图。

一个选项可能是在每个web应用程序中从扫描中排除一些JAR文件。这将阻止tomcat解析所有JAR，并且只查看与手头任务相关的JAR。@christopher:但是如果情况如上所述，web应用程序中只包含相同的共享库，这应该没什么区别。@oschlueter:你能在启动延迟期间获得一些堆栈跟踪（例如使用jstack）来查看发生了什么事情吗？使用探查器并找出花费时间的原因。在我看来，你应该在这里使用

shared.loader=

property-inside

catalina.properties

。尽管在第7版Tomcat的

catalina.properties

中仍然存在此选项，但在提到的

HOW-TO

中省略了此选项。关于它，您可以在以前的Tomcat 5.5文档中阅读：

  Bootstrap
      |
   System
      |
   Common
   /     \
Webapp1   Webapp2 ...

 Bootstrap
      |
   System
      |
   Common
  /      \
Catalina Shared
         /   \
    Webapp1  Webapp2 ...