Tomcat源码分析(一)--初始化init(Bootstrap启动)

今天药忘吃喽~ 2022-05-17 04:43 299阅读 0赞

下载tomcat 8.0源码可以到tomcat官网去下载   source code distributions 选择zip,下载完新建一个pom.xml就可以导入到eclipse中了。其实知道Tomcat源码就可以把spring Web项目整个运行流程就可以想明白。

![70][]

# ***一、Tomcat总体结构*** #

![70 1][]

一个Tomcat中只有一个Server,一个Server可以包含多个Service,一个Service只有一个Cotainer,但可以有多个Connectors,

(因为一个服务可以有多个连接，如同时提供http和https连接，也可以提供相同协议不同端口的接口)

Tomcat最顶层的容器就叫Server,代表整个服务器,Server包含一个或多个的Service.

Service包括了Connector和Container.

Tomcat里的Server由org.apache,catalina.startup.Catalina来管理。Catalina类的三个方法start,stop,load分别管理整个服务器的生命周期。

load方法用于根据conf/server.xml文件创建Server并调用Server的init方法进行初始化,

---》 Catalina类的load()方法详细解释在 （[Tomcat源码分析(二)][Tomcat]）

start方法用于启动服务器，stop方法用于停止服务器，start和stop都调用了Server的start和stop方法。load方法内部调用了Server的init方法。

Server的start方法--->所有的Service中的start方法-->调用所有包含Connector和Container的start方法-》启动了服务器

init和stop方法也是一样。

/**
         * Await and shutdown.
         */
        public void await() {
    
            getServer().await();
    
        }

Catalina的await方法--》Server的await方法 作用是进入一个循环，让主线程不会退出。

# ***二、Tomcat的启动入口*** #

Catalina类主要负责 具体的管理类，而Bootstrap类是启动的入口(main方法)。

Bootstrap类main方法：

/**
         * Main method and entry point when starting Tomcat via the provided
         * scripts.
         *
         * @param args Command line arguments to be processed
         */
        public static void main(String args[]) {
    
            if (daemon == null) {
                // Don't set daemon until init() has completed
                Bootstrap bootstrap = new Bootstrap();
                try {
                    bootstrap.init();
                } catch (Throwable t) {
                    handleThrowable(t);
                    t.printStackTrace();
                    return;
                }
                daemon = bootstrap;
            } else {
                // When running as a service the call to stop will be on a new
                // thread so make sure the correct class loader is used to prevent
                // a range of class not found exceptions.
                Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
            }
    
            try {
                String command = "start";
                if (args.length > 0) {
                    command = args[args.length - 1];
                }
    
                if (command.equals("startd")) {
                    args[args.length - 1] = "start";
                    daemon.load(args);
                    daemon.start();
                } else if (command.equals("stopd")) {
                    args[args.length - 1] = "stop";
                    daemon.stop();
                } else if (command.equals("start")) {
                    daemon.setAwait(true);
                    daemon.load(args);
                    daemon.start();
                } else if (command.equals("stop")) {
                    daemon.stopServer(args);
                } else if (command.equals("configtest")) {
                    daemon.load(args);
                    if (null==daemon.getServer()) {
                        System.exit(1);
                    }
                    System.exit(0);
                } else {
                    log.warn("Bootstrap: command \"" + command + "\" does not exist.");
                }
            } catch (Throwable t) {
                // Unwrap the Exception for clearer error reporting
                if (t instanceof InvocationTargetException &&
                        t.getCause() != null) {
                    t = t.getCause();
                }
                handleThrowable(t);
                t.printStackTrace();
                System.exit(1);
            }
    
        }

如果args参数为空，默认执行start。

main方法内：

bootstrap.init();

具体的实现init()方法：

/**
         * Initialize daemon.
         */
        public void init() throws Exception {
    
            initClassLoaders();
    
            Thread.currentThread().setContextClassLoader(catalinaLoader);
    
            SecurityClassLoad.securityClassLoad(catalinaLoader);
    
            // Load our startup class and call its process() method
            if (log.isDebugEnabled())
                log.debug("Loading startup class");
            Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
            Object startupInstance = startupClass.getConstructor().newInstance();
    
            // Set the shared extensions class loader
            if (log.isDebugEnabled())
                log.debug("Setting startup class properties");
            String methodName = "setParentClassLoader";
            Class<?> paramTypes[] = new Class[1];
            paramTypes[0] = Class.forName("java.lang.ClassLoader");
            Object paramValues[] = new Object[1];
            paramValues[0] = sharedLoader;
            Method method =
                startupInstance.getClass().getMethod(methodName, paramTypes);
            method.invoke(startupInstance, paramValues);
    
            catalinaDaemon = startupInstance;
    
        }

**1、初始化ClassLoader（initClassLoaders）**

**     ** 创建commonLoader、catalinaLoader和sharedLoader;

代码如下:

private void initClassLoaders() {
            try {
                commonLoader = createClassLoader("common", null);
                if( commonLoader == null ) {
                    // no config file, default to this loader - we might be in a 'single' env.
                    commonLoader=this.getClass().getClassLoader();
                }
                catalinaLoader = createClassLoader("server", commonLoader); //这里如果获取不到server.loader对应的value值就会返回commonLoader。
                sharedLoader = createClassLoader("shared", commonLoader);
            } catch (Throwable t) {
                handleThrowable(t);
                log.error("Class loader creation threw exception", t);
                System.exit(1);
            }
        }

createClassLoader方法

代码如下:

private ClassLoader createClassLoader(String name, ClassLoader parent)
            throws Exception {
    
            String value = CatalinaProperties.getProperty(name + ".loader");
            if ((value == null) || (value.equals("")))
                return parent;
    
            value = replace(value);
    
            List<Repository> repositories = new ArrayList<>();
    
            String[] repositoryPaths = getPaths(value);
    
            for (String repository : repositoryPaths) {
                // Check for a JAR URL repository
                try {
                    @SuppressWarnings("unused")
                    URL url = new URL(repository);
                    repositories.add(
                            new Repository(repository, RepositoryType.URL));
                    continue;
                } catch (MalformedURLException e) {
                    // Ignore
                }
    
                // Local repository
                if (repository.endsWith("*.jar")) {
                    repository = repository.substring
                        (0, repository.length() - "*.jar".length());
                    repositories.add(
                            new Repository(repository, RepositoryType.GLOB));
                } else if (repository.endsWith(".jar")) {
                    repositories.add(
                            new Repository(repository, RepositoryType.JAR));
                } else {
                    repositories.add(
                            new Repository(repository, RepositoryType.DIR));
                }
            }
    
            return ClassLoaderFactory.createClassLoader(repositories, parent);
        }

ClassLoaderFactory类的ClassLoaderFactory.createClassLoader(repositories, parent);具体实现代码如下：

/**
         * Create and return a new class loader, based on the configuration
         * defaults and the specified directory paths:
         *
         * @param repositories List of class directories, jar files, jar directories
         *                     or URLS that should be added to the repositories of
         *                     the class loader.
         * @param parent Parent class loader for the new class loader, or
         *  <code>null</code> for the system class loader.
         *
         * @exception Exception if an error occurs constructing the class loader
         */
        public static ClassLoader createClassLoader(List<Repository> repositories,
                                                    final ClassLoader parent)
            throws Exception {
    
            if (log.isDebugEnabled())
                log.debug("Creating new class loader");
    
            // Construct the "class path" for this class loader
            Set<URL> set = new LinkedHashSet<>();
    
            if (repositories != null) {
                for (Repository repository : repositories)  {
                    if (repository.getType() == RepositoryType.URL) {
                        URL url = buildClassLoaderUrl(repository.getLocation());
                        if (log.isDebugEnabled())
                            log.debug("  Including URL " + url);
                        set.add(url);
                    } else if (repository.getType() == RepositoryType.DIR) {
                        File directory = new File(repository.getLocation());
                        directory = directory.getCanonicalFile();
                        if (!validateFile(directory, RepositoryType.DIR)) {
                            continue;
                        }
                        URL url = buildClassLoaderUrl(directory);
                        if (log.isDebugEnabled())
                            log.debug("  Including directory " + url);
                        set.add(url);
                    } else if (repository.getType() == RepositoryType.JAR) {
                        File file=new File(repository.getLocation());
                        file = file.getCanonicalFile();
                        if (!validateFile(file, RepositoryType.JAR)) {
                            continue;
                        }
                        URL url = buildClassLoaderUrl(file);
                        if (log.isDebugEnabled())
                            log.debug("  Including jar file " + url);
                        set.add(url);
                    } else if (repository.getType() == RepositoryType.GLOB) {
                        File directory=new File(repository.getLocation());
                        directory = directory.getCanonicalFile();
                        if (!validateFile(directory, RepositoryType.GLOB)) {
                            continue;
                        }
                        if (log.isDebugEnabled())
                            log.debug("  Including directory glob "
                                + directory.getAbsolutePath());
                        String filenames[] = directory.list();
                        if (filenames == null) {
                            continue;
                        }
                        for (int j = 0; j < filenames.length; j++) {
                            String filename = filenames[j].toLowerCase(Locale.ENGLISH);
                            if (!filename.endsWith(".jar"))
                                continue;
                            File file = new File(directory, filenames[j]);
                            file = file.getCanonicalFile();
                            if (!validateFile(file, RepositoryType.JAR)) {
                                continue;
                            }
                            if (log.isDebugEnabled())
                                log.debug("    Including glob jar file "
                                    + file.getAbsolutePath());
                            URL url = buildClassLoaderUrl(file);
                            set.add(url);
                        }
                    }
                }
            }
    
            // Construct the class loader itself
            final URL[] array = set.toArray(new URL[set.size()]);
            if (log.isDebugEnabled())
                for (int i = 0; i < array.length; i++) {
                    log.debug("  location " + i + " is " + array[i]);
                }
    
            return AccessController.doPrivileged(
                    new PrivilegedAction<URLClassLoader>() {
                        @Override
                        public URLClassLoader run() {
                            if (parent == null)
                                return new URLClassLoader(array);
                            else
                                return new URLClassLoader(array, parent);
                        }
                    });
        }

把从catalina.properties文件中拿到的xx.loader对应的value值，组装成URLClassLoader对象。

具体的new URLClassLoader(array);实现如下：

public URLClassLoader(URL[] urls) {
            super();
            // this is to make the stack depth consistent with 1.1
            SecurityManager security = System.getSecurityManager();
            if (security != null) {
                security.checkCreateClassLoader();
            }
            this.acc = AccessController.getContext();
            ucp = new URLClassPath(urls, acc);
        }

CatalinaProperties类的getProperty方法获取 loader.

/**
         * Return specified property value.
         */
        public static String getProperty(String name) {
            return properties.getProperty(name);
        }

CatalinaProperties类在在类初次被加载的时候调用了loadProperties();

static {
            loadProperties();
        }

/**
         * Load properties.加载配置信息 
         */
        private static void loadProperties() {
    
            InputStream is = null;
            Throwable error = null;
    
            try { //从系统变量中查找
                String configUrl = System.getProperty("catalina.config");
                if (configUrl != null) {
                    is = (new URL(configUrl)).openStream();
                }
            } catch (Throwable t) {
                handleThrowable(t);
            }
    
            if (is == null) { //从tomcat的conf目录下找到catalina.properties文件加载
                try {
                    File home = new File(Bootstrap.getCatalinaBase());
                    File conf = new File(home, "conf");
                    File propsFile = new File(conf, "catalina.properties");
                    is = new FileInputStream(propsFile);
                } catch (Throwable t) {
                    handleThrowable(t);
                }
            }
    
            if (is == null) { //从类路径中加载
                try {
                    is = CatalinaProperties.class.getResourceAsStream
                        ("/org/apache/catalina/startup/catalina.properties");
                } catch (Throwable t) {
                    handleThrowable(t);
                }
            }
    
            if (is != null) { //如果已经找到则加载
                try {
                    properties = new Properties();
                    properties.load(is);
                } catch (Throwable t) {
                    handleThrowable(t);
                    error = t;
                } finally {
                    try {
                        is.close();
                    } catch (IOException ioe) {
                        log.warn("Could not close catalina.properties", ioe);
                    }
                }
            }
    
            if ((is == null) || (error != null)) {
                // Do something
                log.warn("Failed to load catalina.properties", error);
                // That's fine - we have reasonable defaults.
                properties = new Properties();
            }
    
            // Register the properties as system properties
            //将这些配置变量注册为系统变量
            Enumeration<?> enumeration = properties.propertyNames();
            while (enumeration.hasMoreElements()) {
                String name = (String) enumeration.nextElement();
                String value = properties.getProperty(name);
                if (value != null) {
                    System.setProperty(name, value);
                }
            }
        }

System.getProperty("catalina.config"):

System.getProperty 就是从系统的变量中获取值。

<table> 
 <tbody> 
  <tr> 
   <td style="vertical-align:middle;">序号</td> 
   <td style="vertical-align:middle;">属性</td> 
   <td style="vertical-align:middle;">说明</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">1</td> 
   <td style="vertical-align:middle;">java.version</td> 
   <td style="vertical-align:middle;">Java&nbsp;运行时环境版本</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">2</td> 
   <td style="vertical-align:middle;">java.vendor</td> 
   <td style="vertical-align:middle;">Java&nbsp;运行时环境供应商</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">3</td> 
   <td style="vertical-align:middle;">java.vendor.url</td> 
   <td style="vertical-align:middle;">Java&nbsp;供应商的 URL</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">4</td> 
   <td style="vertical-align:middle;">java.home</td> 
   <td style="vertical-align:middle;">Java&nbsp;安装目录</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">5</td> 
   <td style="vertical-align:middle;">java.vm.specification.version</td> 
   <td style="vertical-align:middle;">Java&nbsp;虚拟机规范版本</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">6</td> 
   <td style="vertical-align:middle;">java.vm.specification.vendor</td> 
   <td style="vertical-align:middle;">Java&nbsp;虚拟机规范供应商</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">7</td> 
   <td style="vertical-align:middle;">java.vm.specification.name</td> 
   <td style="vertical-align:middle;">Java&nbsp;虚拟机规范名称</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">8</td> 
   <td style="vertical-align:middle;">java.vm.version</td> 
   <td style="vertical-align:middle;">Java&nbsp;虚拟机实现版本</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">9</td> 
   <td style="vertical-align:middle;">java.vm.vendor</td> 
   <td style="vertical-align:middle;">Java&nbsp;虚拟机实现供应商</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">10</td> 
   <td style="vertical-align:middle;">java.vm.name</td> 
   <td style="vertical-align:middle;">Java&nbsp;虚拟机实现名称</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">11</td> 
   <td style="vertical-align:middle;">java.specification.version</td> 
   <td style="vertical-align:middle;">Java&nbsp;运行时环境规范版本</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">12</td> 
   <td style="vertical-align:middle;">java.specification.vendor</td> 
   <td style="vertical-align:middle;">Java&nbsp;运行时环境规范供应商</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">13</td> 
   <td style="vertical-align:middle;">java.specification.name</td> 
   <td style="vertical-align:middle;">Java&nbsp;运行时环境规范名称</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">14</td> 
   <td style="vertical-align:middle;">java.class.version</td> 
   <td style="vertical-align:middle;">Java&nbsp;类格式版本号</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">15</td> 
   <td style="vertical-align:middle;">java.class.path</td> 
   <td style="vertical-align:middle;">Java&nbsp;类路径</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">16</td> 
   <td style="vertical-align:middle;">java.library.path</td> 
   <td style="vertical-align:middle;">加载库时搜索的路径列表</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">17</td> 
   <td style="vertical-align:middle;">java.io.tmpdir</td> 
   <td style="vertical-align:middle;">默认的临时文件路径</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">18</td> 
   <td style="vertical-align:middle;">java.compiler</td> 
   <td style="vertical-align:middle;">要使用的 JIT 编译器的名称</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">19</td> 
   <td style="vertical-align:middle;">java.ext.dirs</td> 
   <td style="vertical-align:middle;">一个或多个扩展目录的路径</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">20</td> 
   <td style="vertical-align:middle;">os.name</td> 
   <td style="vertical-align:middle;">操作系统的名称</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">21</td> 
   <td style="vertical-align:middle;">os.arch</td> 
   <td style="vertical-align:middle;">操作系统的架构</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">22</td> 
   <td style="vertical-align:middle;">os.version</td> 
   <td style="vertical-align:middle;">操作系统的版本</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">23</td> 
   <td style="vertical-align:middle;">file.separator</td> 
   <td style="vertical-align:middle;">文件分隔符（在 UNIX 系统中是“/”）</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">24</td> 
   <td style="vertical-align:middle;">path.separator</td> 
   <td style="vertical-align:middle;">路径分隔符（在 UNIX 系统中是“:”）</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">25</td> 
   <td style="vertical-align:middle;">line.separator</td> 
   <td style="vertical-align:middle;">行分隔符（在 UNIX 系统中是“/n”）</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">26</td> 
   <td style="vertical-align:middle;">user.name</td> 
   <td style="vertical-align:middle;">用户的账户名称</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">27</td> 
   <td style="vertical-align:middle;">user.home</td> 
   <td style="vertical-align:middle;">用户的主目录</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:middle;">28</td> 
   <td style="vertical-align:middle;">user.dir</td> 
   <td style="vertical-align:middle;">用户的当前工作目录</td> 
  </tr> 
 </tbody> 
</table>

` ``System.out.println(``"Java运行环境的版本:"` `+ System.getProperty(``"java.version"``));`

` System.out.println(``"Java运行环境的生产商:"` `+ System.getProperty(``"java.vendor"``));`

` ``System.out.println(``"Java的安装路径："` `+ System.getProperty(``"java.home"``));`

` ``System.out.println(``"虚拟机实现的版本："` `+ System.getProperty(``"java.vm.version"``));`

` ``System.out.println(``"虚拟机实现的生产商："` `+ System.getProperty(``"java.vm.vendor"``));`

` ``System.out.println(``"默认的临时文件路径："` `+ System.getProperty(``"java.io.tmpdir"``));`

` ``System.out.println(``"用户的账户名称："` `+ System.getProperty(``"user.name"``));`

` ``System.out.println(``"当前用户工作目录："` `+ System.getProperty(``"user.dir"``));`

` ``System.out.println(``"用户的home路径："` `+ System.getProperty(``"user.home"``));`

` ``System.out.println(``"操作系统的名称:"` `+ System.getProperty(``"os.name"``));`

` ``System.out.println(``"操作系统的版本："` `+ System.getProperty(``"os.version"``));`

` System.out.println(``"操作系统的架构："` `+ System.getProperty(``"os.arch"``));`

` ``System.out.println(``"运行环境规范的名称:"` `+ System.getProperty(``"java.specification.name"``));`

` ``System.out.println(``"Java类格式化的版本号："` `+ System.getProperty(``"java.class.version"``));`

` ``System.out.println(``"类所在的路径："` `+ System.getProperty(``"java.class.path"``));`

当然还可以通过System.setProperty方法set值，如：System.setProperty("jdbc.drivers","aaa.bbb.ccc");

System.setProperty(name, value);

如果从tomcat的conf目录下找到加载：代码如下：

if (is == null) { //从tomcat的conf目录下找到catalina.properties文件加载
                try {
                    File home = new File(Bootstrap.getCatalinaBase());
                    File conf = new File(home, "conf");
                    File propsFile = new File(conf, "catalina.properties");
                    is = new FileInputStream(propsFile);
                } catch (Throwable t) {
                    handleThrowable(t);
                }
            }

那么catalina.properties文件内容如下:

# Licensed to the Apache Software Foundation (ASF) under one or more
    # contributor license agreements.  See the NOTICE file distributed with
    # this work for additional information regarding copyright ownership.
    # The ASF licenses this file to You under the Apache License, Version 2.0
    # (the "License"); you may not use this file except in compliance with
    # the License.  You may obtain a copy of the License at
    #
    #     http://www.apache.org/licenses/LICENSE-2.0
    #
    # Unless required by applicable law or agreed to in writing, software
    # distributed under the License is distributed on an "AS IS" BASIS,
    # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    # See the License for the specific language governing permissions and
    # limitations under the License.
    
    #
    # List of comma-separated packages that start with or equal this string
    # will cause a security exception to be thrown when
    # passed to checkPackageAccess unless the
    # corresponding RuntimePermission ("accessClassInPackage."+package) has
    # been granted.
    package.access=sun.,org.apache.catalina.,org.apache.coyote.,org.apache.jasper.,org.apache.tomcat.
    #
    # List of comma-separated packages that start with or equal this string
    # will cause a security exception to be thrown when
    # passed to checkPackageDefinition unless the
    # corresponding RuntimePermission ("defineClassInPackage."+package) has
    # been granted.
    #
    # by default, no packages are restricted for definition, and none of
    # the class loaders supplied with the JDK call checkPackageDefinition.
    #
    package.definition=sun.,java.,org.apache.catalina.,org.apache.coyote.,\
    org.apache.jasper.,org.apache.naming.,org.apache.tomcat.
    
    #
    #
    # List of comma-separated paths defining the contents of the "common"
    # classloader. Prefixes should be used to define what is the repository type.
    # Path may be relative to the CATALINA_HOME or CATALINA_BASE path or absolute.
    # If left as blank,the JVM system loader will be used as Catalina's "common"
    # 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
    #
    # Note: Values are enclosed in double quotes ("...") in case either the
    #       ${catalina.base} path or the ${catalina.home} path contains a comma.
    #       Because double quotes are used for quoting, the double quote character
    #       may not appear in a path.
    common.loader="${catalina.base}/lib","${catalina.base}/lib/*.jar","${catalina.home}/lib","${catalina.home}/lib/*.jar"
    
    #
    # List of comma-separated paths defining the contents of the "server"
    # classloader. Prefixes should be used to define what is the repository type.
    # Path may be relative to the CATALINA_HOME or CATALINA_BASE path or absolute.
    # If left as blank, the "common" loader will be used as Catalina's "server"
    # 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
    #
    # Note: Values may be enclosed in double quotes ("...") in case either the
    #       ${catalina.base} path or the ${catalina.home} path contains a comma.
    #       Because double quotes are used for quoting, the double quote character
    #       may not appear in a path.
    server.loader=
    
    #
    # 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:.
    #
    # Note: Values may be enclosed in double quotes ("...") in case either the
    #       ${catalina.base} path or the ${catalina.home} path contains a comma.
    #       Because double quotes are used for quoting, the double quote character
    #       may not appear in a path.
    shared.loader=
    
    # Default list of JAR files that should not be scanned using the JarScanner
    # functionality. This is typically used to scan JARs for configuration
    # information. JARs that do not contain such information may be excluded from
    # the scan to speed up the scanning process. This is the default list. JARs on
    # this list are excluded from all scans. The list must be a comma separated list
    # of JAR file names.
    # The list of JARs to skip may be over-ridden at a Context level for individual
    # scan types by configuring a JarScanner with a nested JarScanFilter.
    # The JARs listed below include:
    # - Tomcat Bootstrap JARs
    # - Tomcat API JARs
    # - Catalina JARs
    # - Jasper JARs
    # - Tomcat JARs
    # - Common non-Tomcat JARs
    # - Test JARs (JUnit, Cobertura and dependencies)
    tomcat.util.scan.StandardJarScanFilter.jarsToSkip=\
    bootstrap.jar,commons-daemon.jar,tomcat-juli.jar,\
    annotations-api.jar,el-api.jar,jsp-api.jar,servlet-api.jar,websocket-api.jar,\
    catalina.jar,catalina-ant.jar,catalina-ha.jar,catalina-storeconfig.jar,\
    catalina-tribes.jar,\
    jasper.jar,jasper-el.jar,ecj-*.jar,\
    tomcat-api.jar,tomcat-util.jar,tomcat-util-scan.jar,tomcat-coyote.jar,\
    tomcat-dbcp.jar,tomcat-jni.jar,tomcat-websocket.jar,\
    tomcat-i18n-en.jar,tomcat-i18n-es.jar,tomcat-i18n-fr.jar,tomcat-i18n-ja.jar,\
    tomcat-juli-adapters.jar,catalina-jmx-remote.jar,catalina-ws.jar,\
    tomcat-jdbc.jar,\
    tools.jar,\
    commons-beanutils*.jar,commons-codec*.jar,commons-collections*.jar,\
    commons-dbcp*.jar,commons-digester*.jar,commons-fileupload*.jar,\
    commons-httpclient*.jar,commons-io*.jar,commons-lang*.jar,commons-logging*.jar,\
    commons-math*.jar,commons-pool*.jar,\
    jstl.jar,taglibs-standard-spec-*.jar,\
    geronimo-spec-jaxrpc*.jar,wsdl4j*.jar,\
    ant.jar,ant-junit*.jar,aspectj*.jar,jmx.jar,h2*.jar,hibernate*.jar,httpclient*.jar,\
    jmx-tools.jar,jta*.jar,log4j*.jar,mail*.jar,slf4j*.jar,\
    xercesImpl.jar,xmlParserAPIs.jar,xml-apis.jar,\
    junit.jar,junit-*.jar,ant-launcher.jar,\
    cobertura-*.jar,asm-*.jar,dom4j-*.jar,icu4j-*.jar,jaxen-*.jar,jdom-*.jar,\
    jetty-*.jar,oro-*.jar,servlet-api-*.jar,tagsoup-*.jar,xmlParserAPIs-*.jar,\
    xom-*.jar
    
    # Default list of JAR files that should be scanned that overrides the default
    # jarsToSkip list above. This is typically used to include a specific JAR that
    # has been excluded by a broad file name pattern in the jarsToSkip list.
    # The list of JARs to scan may be over-ridden at a Context level for individual
    # scan types by configuring a JarScanner with a nested JarScanFilter.
    tomcat.util.scan.StandardJarScanFilter.jarsToScan=\
    log4j-web*.jar,log4j-taglib*.jar,log4javascript*.jar,slf4j-taglib*.jar
    
    # String cache configuration.
    tomcat.util.buf.StringCache.byte.enabled=true
    #tomcat.util.buf.StringCache.char.enabled=true
    #tomcat.util.buf.StringCache.trainThreshold=500000
    #tomcat.util.buf.StringCache.cacheSize=5000
    
    # This system property is deprecated. Use the relaxedPathChars relaxedQueryChars
    # attributes of the Connector instead. These attributes permit a wider range of
    # characters to be configured as valid.
    # Allow for changes to HTTP request validation
    # WARNING: Using this option may expose the server to CVE-2016-6816
    #tomcat.util.http.parser.HttpParser.requestTargetAllow=|

其中包含了 common.loader,

server.loader,

shared.loader,

tomcat.util.scan.StandardJarScanFilter.jarsToSkip,

tomcat.util.scan.StandardJarScanFilter.jarsToScan,

tomcat.util.buf.StringCache.byte.enabled,

这些key值，在调用loadProperties方法的时候都会加载存储在Properties properties里。

$\{catalina.base\}:

catalina.home指向公用信息的位置，就是bin和lib的父目录。  
catalina.base指向每个Tomcat目录私有信息的位置，就是conf、logs、temp、webapps和work的父目录。

而设置 catalina.base的值和catalina.home的值是在 tomcat\\bin\\catalina.bat文件中catalina.base设置方法。

catalina.bat文件里面设置catalina.base部分代码如下：

rem Guess CATALINA_HOME if not defined
    set "CURRENT_DIR=%cd%"
    if not "%CATALINA_HOME%" == "" goto gotHome
    set "CATALINA_HOME=%CURRENT_DIR%"
    if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome
    cd ..
    set "CATALINA_HOME=%cd%"
    cd "%CURRENT_DIR%"
    :gotHome
    
    if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome
    echo The CATALINA_HOME environment variable is not defined correctly
    echo This environment variable is needed to run this program
    goto end
    :okHome

**2、Thread.currentThread().setContextClassLoader(catalinaLoader);**

主要作用是把catalinaLoader设置为Tomcat主线程的上下文类加载器。

** 3、SecurityClassLoad.securityClassLoad(catalinaLoader);线程安全的加载class(类)**

**SecurityClassLoad类：**

public static void securityClassLoad(ClassLoader loader) throws Exception {
            securityClassLoad(loader, true);
        }
    
        static void securityClassLoad(ClassLoader loader, boolean requireSecurityManager) throws Exception {
    
            if (requireSecurityManager && System.getSecurityManager() == null) {
                return;
            }
    
            loadCorePackage(loader);
            loadCoyotePackage(loader);
            loadLoaderPackage(loader);
            loadRealmPackage(loader);
            loadServletsPackage(loader);
            loadSessionPackage(loader);
            loadUtilPackage(loader);
            loadValvesPackage(loader);
            loadWebResourcesPackage(loader);
            loadJavaxPackage(loader);
            loadConnectorPackage(loader);
            loadTomcatPackage(loader);
        }

private static final void loadCorePackage(ClassLoader loader) throws Exception {
            final String basePackage = "org.apache.catalina.core.";
            loader.loadClass(basePackage + "AccessLogAdapter");
            loadAnonymousInnerClasses(loader, basePackage + "ApplicationContextFacade");//加载匿名内部类
            loader.loadClass(basePackage + "ApplicationDispatcher$PrivilegedForward");
            loader.loadClass(basePackage + "ApplicationDispatcher$PrivilegedInclude");
            loader.loadClass(basePackage + "AsyncContextImpl");
            loader.loadClass(basePackage + "AsyncContextImpl$DebugException");
            loadAnonymousInnerClasses(loader, basePackage + "AsyncContextImpl");
            loader.loadClass(basePackage + "AsyncListenerWrapper");
            loader.loadClass(basePackage + "ContainerBase$PrivilegedAddChild");
            loadAnonymousInnerClasses(loader, basePackage + "DefaultInstanceManager");
            loader.loadClass(basePackage + "DefaultInstanceManager$AnnotationCacheEntry");
            loader.loadClass(basePackage + "DefaultInstanceManager$AnnotationCacheEntryType");
            loader.loadClass(basePackage + "ApplicationHttpRequest$AttributeNamesEnumerator");
        }

loadCorePackage 加载org.apache.catalina.core.路径下的类包括 AccessLogAdapter，ApplicationContextFacade...

**4.使用反射调用了org.apache.catalina.startup.Catalina类的构造方法。**

// Load our startup class and call its process() method
            if (log.isDebugEnabled())
                log.debug("Loading startup class");
            Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
            Object startupInstance = startupClass.getConstructor().newInstance();

**5.使用Method反射调用org.apache.catalina.startup.Catalina类的setParentClassLoader方法并且参数是sharedLoader。**

// Set the shared extensions class loader
            if (log.isDebugEnabled())
                log.debug("Setting startup class properties");
            String methodName = "setParentClassLoader";
            Class<?> paramTypes[] = new Class[1];
            paramTypes[0] = Class.forName("java.lang.ClassLoader");
            Object paramValues[] = new Object[1];
            paramValues[0] = sharedLoader;
            Method method =
                startupInstance.getClass().getMethod(methodName, paramTypes);
            method.invoke(startupInstance, paramValues);

[70]: /images/20220517/a7098e4c2c044f4b927ba78cc0b1e5f1.png
[70 1]: /images/20220517/b4d84a17b1f64ea79e967a01294119df.png
[Tomcat]: https://blog.csdn.net/Jacabe/article/details/81610984