Tomcat9如何加載server.xml-創新互聯

小編給大家分享一下Tomcat9如何加載server.xml，相信大部分人都還不怎么了解，因此分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后大有收獲，下面讓我們一起去了解一下吧！

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1.Tomcat啟動

org.apache.catalina.startup.Bootstrap.main(String args[])

 public static void main(String args[]) {
        synchronized (daemonLock) {
            if (daemon == null) {
                Bootstrap bootstrap = new Bootstrap();
                try {
                    bootstrap.init(); //初始化類加載器
                } catch (Throwable t) {
                    handleThrowable(t);
                    t.printStackTrace();
                    return;
                }
                daemon = bootstrap;
            } else {
                Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
            }
        }
        //根據傳入的不同指令，進行相應處理
        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();
                if (null == daemon.getServer()) {
                    System.exit(1);
                }
            } 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) {
            if (t instanceof InvocationTargetException &&
                    t.getCause() != null) {
                t = t.getCause();
            }
            handleThrowable(t);
            t.printStackTrace();
            System.exit(1);
        }
    }

在main方法中主要為兩部分邏輯：

調用bootstrap.init()進行初始化
根據傳入不同的指令進行相應的處理，本文主要分析start指定，即服務啟動。啟動服務start主要調用了org.apache.catalina.startup.Catalina.load()和start()方法

org.apache.catalina.startup.Bootstrap.init()

 public void init() throws Exception {
        initClassLoaders(); //初始化類加載
        Thread.currentThread().setContextClassLoader(catalinaLoader); //設置當前線程的類加載器為catalinaLoader
        SecurityClassLoad.securityClassLoad(catalinaLoader); //啟用java安全管理的處理
        //通過反射的方式實例化org.apache.catalina.startup.Catalina，并設置父類加載器為sharedLoader
        if (log.isDebugEnabled())
            log.debug("Loading startup class");
        Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.getConstructor().newInstance();
        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;
    }

類加載器的初始化，創建commonLoader、catalinaLoader、sharedLoader，具體可參考上一篇《Tomcat9源代碼淺析-類加載體系》
啟用java安全管理的處理
通過反射的方式實例化org.apache.catalina.startup.Catalina，并設置父類加載器為sharedLoader

org.apache.catalina.security.SecurityClassLoad

public final class SecurityClassLoad {
    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);
        loadJavaxPackage(loader);
        loadConnectorPackage(loader);
        loadTomcatPackage(loader);
    }

當時使用Java SecurityManager時，會提前加載一些必要的java類，以避免觸發權限異常AccessControlException

2.server.xml解析框架

2.1 SAX

Tomcat中使用SAX解析server.xml文件。SAX解析方式會逐行的解析XML文檔，當遇到標簽時會觸發解析處理器，采用事件處理的方式解析XML，它的優點是不需要將完整的XML文檔加載進內存，可以在讀取文檔的同時就進行解析，節省內存，適合解析超大XML，主要方法有：

startDocument()：文檔解析開始時調用，該方法只會調用一次
startElement(String uri, String localName, String qName, Attributes attributes):標簽解析開始時調用
endElement(String uri, String localName, String qName)：標簽（節點）解析結束后調用
endDocument()：文檔解析結束后調用，該方法只會調用一次

2.2 規則Rules

Tomcat9如何加載server.xml
Tomcat將server.xml的解析抽象為規則，利用Java的引用傳遞，通過有副作用的void方法，對xml進行解析，規則調用的順序與xml解析的順序是一致的，即start方法是正序，end方法是逆序。
規則中包含以下方法：

begin：Degister.startElement 方法調用
body、end：Degister.endElement方法中調用，先調用body，再調用end
finish：Degister.endDocument方法中調用

Tomcat中常見的規則類型：

ObjectCreateRule 創建對應class的對象實例，并放到Designer的堆棧成員屬性中
SetPropertiesRule 獲取堆棧中棧頂的元素，并將xml元素的屬性賦值給對象實例
SetNextRule 調用父節點的實例對象，將當前對象作為參數，反射調用某個方法
ListenerCreateRule 當Listener標簽有optional屬性為true時，創建實例異常時，強制添加OptionalListener實例
ConnectorCreateRule 創建Connector實例
SetAllPropertiesRule 主體功能與SetPropertiesRule 一致，這個Rule可以排除一些屬性的設置
AddPortOffsetRule Set portOffset on all the connectors based on portOffset in the Server
CertificateCreateRule 實例化SSLHostConfigCertificate

3.server.xml解析源代碼解析

org.apache.catalina.startup.Catalina.load()

public void load() {
        if (loaded) {
            return;
        }
        loaded = true;
        long t1 = System.nanoTime();
        initDirs();
        // Before digester - it may be needed
        initNaming();
        // 讀取conf/server.xml
        ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(Bootstrap.getCatalinaBaseFile(), getConfigFile()));
        File file = configFile();
        // 創建xml解析Digester 
        Digester digester = createStartDigester();
        try (ConfigurationSource.Resource resource = ConfigFileLoader.getSource().getServerXml()) {
            InputStream inputStream = resource.getInputStream();
            InputSource inputSource = new InputSource(resource.getURI().toURL().toString());
            inputSource.setByteStream(inputStream);
            digester.push(this);
            digester.parse(inputSource); //解析xml
        } catch (Exception e) {
            log.warn(sm.getString("catalina.configFail", file.getAbsolutePath()), e);
            if (file.exists() && !file.canRead()) {
                log.warn(sm.getString("catalina.incorrectPermissions"));
            }
            return;
        }
        //設置server的屬性
        getServer().setCatalina(this);
        getServer().setCatalinaHome(Bootstrap.getCatalinaHomeFile());
        getServer().setCatalinaBase(Bootstrap.getCatalinaBaseFile());
        // Stream redirection
        initStreams();
        // 初始化server
        try {
            getServer().init();
        } catch (LifecycleException e) {
            if (Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE")) {
                throw new java.lang.Error(e);
            } else {
                log.error(sm.getString("catalina.initError"), e);
            }
        }
        long t2 = System.nanoTime();
        if(log.isInfoEnabled()) {
            log.info(sm.getString("catalina.init", Long.valueOf((t2 - t1) / 1000000)));
        }
    }

Bootstrap中start指令邏輯，通過反射調用Catalina.load()
Catalina.load() 讀取conf/server.xml，創建解析xml的Digester
開始初始化server

org.apache.catalina.startup.Catalina.createStartDigester()

 protected Digester createStartDigester() {
        long t1=System.currentTimeMillis();
        // Initialize the digester
        Digester digester = new Digester();
        digester.setValidating(false);
        digester.setRulesValidation(true);
        Map<Class<?>, List<String>> fakeAttributes = new HashMap<>();
        // Ignore className on all elements
        List<String> objectAttrs = new ArrayList<>();
        objectAttrs.add("className");
        fakeAttributes.put(Object.class, objectAttrs);
        // Ignore attribute added by Eclipse for its internal tracking
        List<String> contextAttrs = new ArrayList<>();
        contextAttrs.add("source");
        fakeAttributes.put(StandardContext.class, contextAttrs);
        // Ignore Connector attribute used internally but set on Server
        List<String> connectorAttrs = new ArrayList<>();
        connectorAttrs.add("portOffset");
        fakeAttributes.put(Connector.class, connectorAttrs);
        digester.setFakeAttributes(fakeAttributes);
        digester.setUseContextClassLoader(true);
        // Configure the actions we will be using
        digester.addObjectCreate("Server",
                                 "org.apache.catalina.core.StandardServer",
                                 "className");
        digester.addSetProperties("Server");
        digester.addSetNext("Server",
                            "setServer",
                            "org.apache.catalina.Server");
        digester.addObjectCreate("Server/GlobalNamingResources",
                                 "org.apache.catalina.deploy.NamingResourcesImpl");
        digester.addSetProperties("Server/GlobalNamingResources");
        digester.addSetNext("Server/GlobalNamingResources",
                            "setGlobalNamingResources",
                            "org.apache.catalina.deploy.NamingResourcesImpl");
        digester.addRule("Server/Listener",
                new ListenerCreateRule(null, "className"));
        digester.addSetProperties("Server/Listener");
        digester.addSetNext("Server/Listener",
                            "addLifecycleListener",
                            "org.apache.catalina.LifecycleListener");
        digester.addObjectCreate("Server/Service",
                                 "org.apache.catalina.core.StandardService",
                                 "className");
        digester.addSetProperties("Server/Service");
        digester.addSetNext("Server/Service",
                            "addService",
                            "org.apache.catalina.Service");
        digester.addObjectCreate("Server/Service/Listener",
                                 null, // MUST be specified in the element
                                 "className");
        digester.addSetProperties("Server/Service/Listener");
        digester.addSetNext("Server/Service/Listener",
                            "addLifecycleListener",
                            "org.apache.catalina.LifecycleListener");
        //Executor
        digester.addObjectCreate("Server/Service/Executor",
                         "org.apache.catalina.core.StandardThreadExecutor",
                         "className");
        digester.addSetProperties("Server/Service/Executor");
        digester.addSetNext("Server/Service/Executor",
                            "addExecutor",
                            "org.apache.catalina.Executor");
        digester.addRule("Server/Service/Connector",
                         new ConnectorCreateRule());
        digester.addRule("Server/Service/Connector", new SetAllPropertiesRule(
                new String[]{"executor", "sslImplementationName", "protocol"}));
        digester.addSetNext("Server/Service/Connector",
                            "addConnector",
                            "org.apache.catalina.connector.Connector");
        digester.addRule("Server/Service/Connector", new AddPortOffsetRule());
        digester.addObjectCreate("Server/Service/Connector/SSLHostConfig",
                                 "org.apache.tomcat.util.net.SSLHostConfig");
        digester.addSetProperties("Server/Service/Connector/SSLHostConfig");
        digester.addSetNext("Server/Service/Connector/SSLHostConfig",
                "addSslHostConfig",
                "org.apache.tomcat.util.net.SSLHostConfig");
        digester.addRule("Server/Service/Connector/SSLHostConfig/Certificate",
                         new CertificateCreateRule());
        digester.addRule("Server/Service/Connector/SSLHostConfig/Certificate",
                         new SetAllPropertiesRule(new String[]{"type"}));
        digester.addSetNext("Server/Service/Connector/SSLHostConfig/Certificate",
                            "addCertificate",
                            "org.apache.tomcat.util.net.SSLHostConfigCertificate");
        digester.addObjectCreate("Server/Service/Connector/SSLHostConfig/OpenSSLConf",
                                 "org.apache.tomcat.util.net.openssl.OpenSSLConf");
        digester.addSetProperties("Server/Service/Connector/SSLHostConfig/OpenSSLConf");
        digester.addSetNext("Server/Service/Connector/SSLHostConfig/OpenSSLConf",
                            "setOpenSslConf",
                            "org.apache.tomcat.util.net.openssl.OpenSSLConf");
        digester.addObjectCreate("Server/Service/Connector/SSLHostConfig/OpenSSLConf/OpenSSLConfCmd",
                                 "org.apache.tomcat.util.net.openssl.OpenSSLConfCmd");
        digester.addSetProperties("Server/Service/Connector/SSLHostConfig/OpenSSLConf/OpenSSLConfCmd");
        digester.addSetNext("Server/Service/Connector/SSLHostConfig/OpenSSLConf/OpenSSLConfCmd",
                            "addCmd",
                            "org.apache.tomcat.util.net.openssl.OpenSSLConfCmd");
        digester.addObjectCreate("Server/Service/Connector/Listener",
                                 null, // MUST be specified in the element
                                 "className");
        digester.addSetProperties("Server/Service/Connector/Listener");
        digester.addSetNext("Server/Service/Connector/Listener",
                            "addLifecycleListener",
                            "org.apache.catalina.LifecycleListener");
        digester.addObjectCreate("Server/Service/Connector/UpgradeProtocol",
                                  null, // MUST be specified in the element
                                  "className");
        digester.addSetProperties("Server/Service/Connector/UpgradeProtocol");
        digester.addSetNext("Server/Service/Connector/UpgradeProtocol",
                            "addUpgradeProtocol",
                            "org.apache.coyote.UpgradeProtocol");
        // Add RuleSets for nested elements
        digester.addRuleSet(new NamingRuleSet("Server/GlobalNamingResources/"));
        digester.addRuleSet(new EngineRuleSet("Server/Service/"));
        digester.addRuleSet(new HostRuleSet("Server/Service/Engine/"));
        digester.addRuleSet(new ContextRuleSet("Server/Service/Engine/Host/"));
        addClusterRuleSet(digester, "Server/Service/Engine/Host/Cluster/");
        digester.addRuleSet(new NamingRuleSet("Server/Service/Engine/Host/Context/"));
        // When the 'engine' is found, set the parentClassLoader.
        digester.addRule("Server/Service/Engine",
                         new SetParentClassLoaderRule(parentClassLoader));
        addClusterRuleSet(digester, "Server/Service/Engine/Cluster/");
        long t2=System.currentTimeMillis();
        if (log.isDebugEnabled()) {
            log.debug("Digester for server.xml created " + ( t2-t1 ));
        }
        return digester;
    }

此方法創建解析server.xml的Digester，根據server.xml的元素標簽，為每個標簽設置相應的規則組，在解析標簽時進行調用。
由此也可以得到結論，server.xml的結構就是Tomcat容器內部的結構，通過對server.xml的解析規則的執行，實例化出Tomcat容器結構。

以下為Tomcat9默認的server.xml

<?xml version="1.0" encoding="UTF-8"?>
<Server port="8005" shutdown="SHUTDOWN">
  <Listener className="org.apache.catalina.startup.VersionLoggerListener" />
  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />
  <GlobalNamingResources>
    <Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
  </GlobalNamingResources>
  <Service name="Catalina">
    <Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />
    <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
    <Engine name="Catalina" defaultHost="localhost">
      <Realm className="org.apache.catalina.realm.LockOutRealm">
        <!-- This Realm uses the UserDatabase configured in the global JNDI
             resources under the key "UserDatabase".  Any edits
             that are performed against this UserDatabase are immediately
             available for use by the Realm.  -->
        <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
               resourceName="UserDatabase"/>
      </Realm>
      <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true">
        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
               prefix="localhost_access_log" suffix=".txt"
               pattern="%h %l %u %t "%r" %s %b" />
      </Host>
    </Engine>
  </Service>
</Server>

其結構見下圖：
Tomcat9如何加載server.xml