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小编给大家分享一下Tomcat9如何加载server.xml，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
public static void main(String args[]) {
synchronized (daemonLock) {
if (daemon == null) {
Bootstrap bootstrap = new Bootstrap();
try {
bootstrap.init(); //初始化类加载器
} catch (Throwable t) {
handleThrowable(t);
t.printStackTrace();
return;
}
daemon = bootstrap;
} else {
Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
}
}
//根据传入的不同指令，进行相应处理
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方法中主要为两部分逻辑：
调用bootstrap.init()进行初始化
根据传入不同的指令进行相应的处理，本文主要分析start指定，即服务启动。启动服务start主要调用了org.apache.catalina.startup.Catalina.load()和start()方法
public void init() throws Exception {
initClassLoaders(); //初始化类加载
Thread.currentThread().setContextClassLoader(catalinaLoader); //设置当前线程的类加载器为catalinaLoader
SecurityClassLoad.securityClassLoad(catalinaLoader); //启用java安全管理的处理
//通过反射的方式实例化org.apache.catalina.startup.Catalina，并设置父类加载器为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;
}类加载器的初始化，创建commonLoader、catalinaLoader、sharedLoader，具体可参考上一篇 《Tomcat9源代码浅析-类加载体系》
启用java安全管理的处理
通过反射的方式实例化org.apache.catalina.startup.Catalina，并设置父类加载器为sharedLoader
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);
}当时使用Java SecurityManager时，会提前加载一些必要的java类，以避免触发权限异常AccessControlException
Tomcat中使用SAX解析server.xml文件。SAX解析方式会逐行的解析XML文档，当遇到标签时会触发解析处理器，采用事件处理的方式解析XML，它的优点是不需要将完整的XML文档加载进内存，可以在读取文档的同时就进行解析，节省内存，适合解析超大XML，主要方法有：
startDocument()：文档解析开始时调用，该方法只会调用一次
startElement(String uri, String localName, String qName, Attributes attributes):标签解析开始时调用
endElement(String uri, String localName, String qName)：标签（节点）解析结束后调用
endDocument()：文档解析结束后调用，该方法只会调用一次
Tomcat将server.xml的解析抽象为规则，利用Java的引用传递，通过有副作用的void方法，对xml进行解析，规则调用的顺序与xml解析的顺序是一致的，即start方法是正序，end方法是逆序。
规则中包含以下方法：
begin：Degister.startElement 方法调用
body、end：Degister.endElement方法中调用，先调用body，再调用end
finish：Degister.endDocument方法中调用
Tomcat中常见的规则类型：
ObjectCreateRule 创建对应class的对象实例，并放到Designer的堆栈成员属性中
SetPropertiesRule 获取堆栈中栈顶的元素，并将xml元素的属性赋值给对象实例
SetNextRule 调用父节点的实例对象，将当前对象作为参数，反射调用某个方法
ListenerCreateRule 当Listener标签有optional属性为true时，创建实例异常时，强制添加OptionalListener实例
ConnectorCreateRule 创建Connector实例
SetAllPropertiesRule 主体功能与SetPropertiesRule 一致，这个Rule可以排除一些属性的设置
AddPortOffsetRule Set portOffset on all the connectors based on portOffset in the Server
CertificateCreateRule 实例化SSLHostConfigCertificate
public void load() {
if (loaded) {
return;
}
loaded = true;
long t1 = System.nanoTime();
initDirs();
// Before digester - it may be needed
initNaming();
// 读取conf/server.xml
ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(Bootstrap.getCatalinaBaseFile(), getConfigFile()));
File file = configFile();
// 创建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;
}
//设置server的属性
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指令逻辑，通过反射调用Catalina.load()
Catalina.load() 读取conf/server.xml，创建解析xml的Digester
开始初始化server
protected Digester createStartDigester() {
long t1=System.currentTimeMillis();
// Initialize the digester
Digester digester = new Digester();
digester.setValidating(false);
digester.setRulesValidation(true);
Map, List> fakeAttributes = new HashMap<>();
// Ignore className on all elements
List objectAttrs = new ArrayList<>();
objectAttrs.add("className");
fakeAttributes.put(Object.class, objectAttrs);
// Ignore attribute added by Eclipse for its internal tracking
List contextAttrs = new ArrayList<>();
contextAttrs.add("source");
fakeAttributes.put(StandardContext.class, contextAttrs);
// Ignore Connector attribute used internally but set on Server
List 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;
} 此方法创建解析server.xml的Digester，根据server.xml的元素标签，为每个标签设置相应的规则组，在解析标签时进行调用。
由此也可以得到结论，server.xml的结构就是Tomcat容器内部的结构，通过对server.xml的解析规则的执行，实例化出Tomcat容器结构。
以下为Tomcat9默认的server.xml