Tomcat源码分析 -- 4

sschrodinger

2019/01/07

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参考

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• 《深入剖析 Tomcat》 - 基于Tomcat 4.x
• 《Tomcat 架构解析》刘光瑞 著
• 《大话设计模式》程杰 著
• Tomcat 8.5.x 源码
• Digester 3.0 API

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Digester

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tomcat 使用 Digester 解析并创建应用服务。

Digester 是一款将 XML 转换为 Java 对象的事件驱动型工具，通过流读取 XML 文件，当识别出特定 XML 节点后执行特定的动作：或者创建 Java 对象；或者执行对象的某个方法。

Digester 使用匹配模式指定相关的约定，匹配模式样例如下：

匹配模式	XML节点	描述
a	<a>	匹配所有名字为"a"的根节点，注意嵌套的同名子节点无法匹配
a/b	<a><b>	匹配所有父节点为根节点"a"，名称为"b"的节点。

Digester 使用对象栈在匹配模式满足时对对象进行操作。在文件读取中，如果遇到一个 XML 节点开始的部分，则会触发处理规则事件创建 Java 对象，并将其放入栈中。当处理该节点的子节点时，该对象都将维护在栈中，直到该节点结束，该对象才会弹出对象栈。

Digester 匹配模式确定了合适触发处理操作，处理规则定义了匹配模式时的具体操作，只需实现 org.apache.commons.digester.Rule 接口，就可以自定义事件处理方法。该接口有四个函数，如下表。

函数名	描述
begin()	当读取到匹配节点的开始部分时调用，会将该节点的所有属性作为参数传入
body()	当读取匹配节点的嵌套内容时调用
end()	当读取到匹配节点的结束部分时调用
finish()	当整个parse()方法完成后调用

Digester 实现了部分默认的事件处理函数，部分如下：

方法及参数	描述
addObjectCreate(String pattern, Class clazz)	当匹配到 pattern 模式时，将 clazz 实例化并压入栈
addSetProperties(String pattern)	当匹配到 pattern 模式时，利用 JavaBean 将参数赋值给对象
addSetNext(String pattern, String methodName)	end() 方法调用，找到位于栈顶部对象之后的对象，调用指定的方法，同时将栈顶部对象作为参数传入，用于设置父对象的子对象
addCallMethod(String pattern, String methodName, int paramCount, Class<?>[] paramTypes)	用于在 end() 执行时调用栈顶部对象的某个方法
addCallParam(String pattern, int paramIndex, String attributeName)	与 addCallMethod 配合使用，创建参数

有如下两个个类：

public class Department {
    public Department() {
        // TODO Auto-generated constructor stub
    }
    
    private String name;
    private String code;
    
    private Map<String, String> extension = new HashMap<>();
    private List<User> users = new ArrayList<>();
    
    public String getName() { return name;}
    public void setName(String name) { this.name = name;}
    
    public String getCode() {return code;}
    public void setCode(String code) {this.code = code;}
    
    public void addUser(User user) { this.users.add(user);}
    
    public void putExtension(String name, String value) {this.extension.put(name, value);}
    
    public void print() {
        System.out.println("department name:" + name + ",code:" + code);
        Set<String> keySet = extension.keySet();
        if (keySet.size() > 0) System.out.println("extension info:");
        for (String string : keySet) {
            System.out.println("key:" + string + ",value:" + extension.get(string));
        }
        if (users.size() > 0) {
            System.out.println("user info:");
            for (User user : users) {
                System.out.println(user);
            }
        }
        
    }
}

public class User {
    
    public User() {
        // TODO Auto-generated constructor stub
    }
    
    private String name;
    private String code;
    
    public String getName() { return name;}
    public void setName(String name) { this.name = name;}
    
    public String getCode() {return code;}
    public void setCode(String code) {this.code = code;}
    
    @Override public String toString() {
        return "name:" + name + ",code:" + code;
    }

}

先通过如下 XML 文档将这两个类组织起来：

<?xml version="1.0" encoding="UTF-8"?>
<department name="deptname001" code="deptcode001">
    <user name="username001" code="usercode001"></user>
    <user name="username002" code="usercode002"></user>
    <extension>
        <property-name>director</property-name>
        <propertry-value>joke</propertry-value>
    </extension>
</department>

则我们可以通过如下的 Demo 代码自动生成树状结构的类：

public class digesterDemo {
    public static void main(String[] args) {
        Digester digester = new Digester();
        digester.setValidating(false);
        digester.addObjectCreate("department", Department.class);
        digester.addSetProperties("department");
        digester.addObjectCreate("department/user", User.class);
        digester.addSetProperties("department/user");
        
        digester.addSetNext("department/user", "addUser");

        digester.addCallParam("department/extension/property-name", 0);
        digester.addCallParam("department/extension/propertry-value", 1);
        digester.addCallMethod("department/extension", "putExtension", 2);
        
        try {
            Department department = (Department) digester.parse(new File("test.xml"));
            department.print();
            /**
            output:
            department name:deptname001,code:deptcode001
                extension info:
                    key:director,value:joke
                user info:
                    name:username001,code:usercode001
                    name:username002,code:usercode002

            **/
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
    }
}

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tomcat 启动

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Tomcat 启动的主函数隐藏在or.apache.catalina.startup.Bootstrap中。main函数接受一个命令行参数启动或者关闭服务器，我们只关心启动过程，即 daemon.start() 分支。

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();
            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) {
        // Unwrap the Exception for clearer error reporting
        if (t instanceof InvocationTargetException &&
                t.getCause() != null) {
            t = t.getCause();
        }
        handleThrowable(t);
        t.printStackTrace();
        System.exit(1);
    }

}

主要实现的功能

• 根据 server.xml 加载整个服务器 （Load()方法）
• 加载钩子
• await() 等待
• 等待结束 调用 stop() 方法 结束

daemon.start() 利用反射机制调用 org.apache.catalina.startup.Catalina类的 start() 方法，启动整个服务器。

如下是 Catalina 类的 start() 方法：

public void start() {

    if (getServer() == null) {
        load();
    }

    if (getServer() == null) {
        log.fatal("Cannot start server. Server instance is not configured.");
        return;
    }

    long t1 = System.nanoTime();

    // Start the new server
    try {
        getServer().start();
    } catch (LifecycleException e) {
        log.fatal(sm.getString("catalina.serverStartFail"), e);
        try {
            getServer().destroy();
        } catch (LifecycleException e1) {
            log.debug("destroy() failed for failed Server ", e1);
        }
        return;
    }

    long t2 = System.nanoTime();
    if(log.isInfoEnabled()) {
        log.info("Server startup in " + ((t2 - t1) / 1000000) + " ms");
    }

    // Register shutdown hook
    if (useShutdownHook) {
        if (shutdownHook == null) {
            shutdownHook = new CatalinaShutdownHook();
        }
        Runtime.getRuntime().addShutdownHook(shutdownHook);

        // If JULI is being used, disable JULI's shutdown hook since
        // shutdown hooks run in parallel and log messages may be lost
        // if JULI's hook completes before the CatalinaShutdownHook()
        LogManager logManager = LogManager.getLogManager();
        if (logManager instanceof ClassLoaderLogManager) {
            ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                    false);
        }
    }

    if (await) {
        await();
        stop();
    }
}

Tomcat 结合 Digester 和 LifecycleListener 做了大量的初始化工作。具体的执行函数为protected Digester 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<>();
    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);
    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.addObjectCreate("Server/Listener",
                                 null, // MUST be specified in the element
                                 "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"}));
    digester.addSetNext("Server/Service/Connector",
                            "addConnector",
                            "org.apache.catalina.connector.Connector");

    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);

}

getServer().start()启动server的生命周期到LifecycleState.STARTED状态；stop()方法关闭服务器，将生命周期改变为LifecycleState.DESTROYED。