Tomcat 启动流程
思考集结处 2021-10-30 Tomcat
Tomcat 启动流程
# Tomcat启动流程
有第一篇文章 Tomcat的源码编译 ,我们知道在启动
配置的的时候，MainClass 配置的地址就是org.apache.catalina.startup.Bootstrap，所有要想研究Tomcat的启动流程，那么
就得研究一下这个类。
# 类Bootstrap执行流程
将核心的几个方法进行提取。
# 初始化
bootstrap.init()方法，初始化类加载器。
public void init() throws Exception {
// 初始化类加载器
initClassLoaders();
Thread.currentThread().setContextClassLoader(catalinaLoader);
SecurityClassLoad.securityClassLoad(catalinaLoader);
if (log.isDebugEnabled()) {
log.debug("Loading startup class");
}
// 加载 Catalina 类 创建实例，调用setParentClassLoader 为什么要用反射？
// catalinaLoader.loadClass 可以决定使用那个类加载器
// 当前加载的Bootstrap 的类加载器是 system class loader
// 若通过反射加载，org.apache.catalina.startup.Catalina就在catalinaLoader
Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
//反射创建实例
Object startupInstance = startupClass.getConstructor().newInstance();
if (log.isDebugEnabled()) {
log.debug("Setting startup class properties");
}
// 方法签名
String methodName = "setParentClassLoader";
//构建参数类型
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;
}
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# 类加载initClassLoaders
首先我们来看一下Tomcat中的类加载模型，有俩种，如下图：
由图可知，类加载有俩种模型，左边的是默认的类加载过程，右边的是做了隔离的类加载过程。左边是
Tomcat和应用共享库 ，右边的可以决定是否要共享库。
private void initClassLoaders() {
try {
// 创建common类加载器
commonLoader = createClassLoader("common", null);
if (commonLoader == null) {
//若common类加载为空着取当前的类加载器
commonLoader = this.getClass().getClassLoader();
}
catalinaLoader = createClassLoader("server", commonLoader);
sharedLoader = createClassLoader("shared", commonLoader);
} catch (Throwable t) {
handleThrowable(t);
log.error("Class loader creation threw exception", t);
System.exit(1);
}
}
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由以上代码可知，有一个创建的类加载器的方法，那么各个类型的类加载器都做了什么。我们分析一下这个方法。
// 创建类加载器
private ClassLoader createClassLoader(String name, ClassLoader parent) throws Exception {
//配置文件中获取类加载器
String value = CatalinaProperties.getProperty(name + ".loader");
//若当前类加载器是空的，则返回父类加载器
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);
}
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# 加载
bootstrap.load()方法，该方法只是一个代理，来代理Catalina类，间接调用 Catalina，创建对象树后，然后
调用生命周期的init方法初始化整个对象树。
private void load(String[] arguments) throws Exception {
// Call the load() method
String methodName = "load";
Object param[];
Class<?> paramTypes[];
if (arguments==null || arguments.length==0) {
paramTypes = null;
param = null;
} else {
paramTypes = new Class[1];
paramTypes[0] = arguments.getClass();
param = new Object[1];
param[0] = arguments;
}
Method method =
catalinaDaemon.getClass().getMethod(methodName, paramTypes);
if (log.isDebugEnabled()) {
log.debug("Calling startup class " + method);
}
method.invoke(catalinaDaemon, param);
}
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# 启动
bootstrap.start()方法，该方法只是一个代理，来代理Catalina类，间接调用 Catalina，创建对象树后，然后
启动生命周期的start方法启动整个对象树。
public void start() throws Exception {
// 必须先初始化Catalina
if (catalinaDaemon == null) {
init();
}
// 直接调用catalina的start
Method method = catalinaDaemon.getClass().getMethod("start", (Class [])null);
method.invoke(catalinaDaemon, (Object [])null);
}
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# 停止
bootstrap.stop()方法，该方法只是一个代理，来代理Catalina类，间接调用 Catalina，创建对象树后，然后
停止生命周期的stop方法启动整个对象树。
public void stop() throws Exception {
Method method = catalinaDaemon.getClass().getMethod("stop", (Class []) null);
method.invoke(catalinaDaemon, (Object []) null);
}
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# 类Catalina原理
# load 加载方法：
创建对象树，然后调用init化方法进行初始化操作
public void load() {
//只允许被加载一次
if (loaded) {
return;
}
loaded = true;
long t1 = System.nanoTime();
// 遗留代码
initDirs();
// JNDI 操作 目前的云原生不会用到
initNaming();
// 创建砸蛋器，自动创建组件树
Digester digester = createStartDigester();
InputSource inputSource = null;
InputStream inputStream = null;
File file = null;
try {
try {
file = configFile();
inputStream = new FileInputStream(file);
inputSource = new InputSource(file.toURI().toURL().toString());
} catch (Exception e) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("catalina.configFail", file), e);
}
}
// 构建 server.xml 组件树流
if (inputStream == null) {
try {
inputStream = getClass().getClassLoader()
.getResourceAsStream(getConfigFile());
inputSource = new InputSource
(getClass().getClassLoader()
.getResource(getConfigFile()).toString());
} catch (Exception e) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("catalina.configFail",
getConfigFile()), e);
}
}
}
if (inputStream == null) {
try {
inputStream = getClass().getClassLoader()
.getResourceAsStream("server-embed.xml");
inputSource = new InputSource
(getClass().getClassLoader()
.getResource("server-embed.xml").toString());
} catch (Exception e) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("catalina.configFail",
"server-embed.xml"), e);
}
}
}
if (inputStream == null || inputSource == null) {
if (file == null) {
log.warn(sm.getString("catalina.configFail",
getConfigFile() + "] or [server-embed.xml]"));
} else {
log.warn(sm.getString("catalina.configFail",
file.getAbsolutePath()));
if (file.exists() && !file.canRead()) {
log.warn("Permissions incorrect, read permission is not allowed on the file.");
}
}
return;
}
try {
inputSource.setByteStream(inputStream);
digester.push(this);
// server.xml 定义的整个对象树和监听器都会按照digester的规则创建完成
digester.parse(inputSource);
} catch (SAXParseException spe) {
log.warn("Catalina.start using " + getConfigFile() + ": " +
spe.getMessage());
return;
} catch (Exception e) {
log.warn("Catalina.start using " + getConfigFile() + ": " , e);
return;
}
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
// Ignore
}
}
}
// 设置server对象的属性
getServer().setCatalina(this);
getServer().setCatalinaHome(Bootstrap.getCatalinaHomeFile());
getServer().setCatalinaBase(Bootstrap.getCatalinaBaseFile());
// 重定向系统 输入输出流
initStreams();
// Start the new server
// 进入整个对象树生命周期流程
try {
//初始化
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("Catalina.start", e);
}
}
long t2 = System.nanoTime();
if(log.isInfoEnabled()) {
log.info("Initialization processed in " + ((t2 - t1) / 1000000) + " ms");
}
}
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Digester可以将 server.xml的配置的组件树的对象树进行创建，并且将各个组件的配置进行配置完成。这样的话整个
对象树就进行了自动创建。
//根据 传如的server.xml 创建tomcat的组件 包括 server service
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;
}
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# start 启动方法：
创建对象树，然后启动生命周期的start方法启动整个对象树。
public void start() {
//先初始化
if (getServer() == null) {
load();
}
if (getServer() == null) {
log.fatal("Cannot start server. Server instance is not configured.");
return;
}
long t1 = System.nanoTime();
//启动生命周期中的start
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");
}
// JVM退出钩子
if (useShutdownHook) {
if (shutdownHook == null) {
shutdownHook = new CatalinaShutdownHook();
}
Runtime.getRuntime().addShutdownHook(shutdownHook);
LogManager logManager = LogManager.getLogManager();
if (logManager instanceof ClassLoaderLogManager) {
((ClassLoaderLogManager) logManager).setUseShutdownHook(
false);
}
}
// 主线程等待关闭信号
if (await) {
await();
stop();
}
}
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# stop 停止方法：
该方法。将组件停止，并且进行销毁。
public void stop() {
try {
if (useShutdownHook) {
Runtime.getRuntime().removeShutdownHook(shutdownHook);
LogManager logManager = LogManager.getLogManager();
if (logManager instanceof ClassLoaderLogManager) {
((ClassLoaderLogManager) logManager).setUseShutdownHook(
true);
}
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
}
try {
Server s = getServer();
LifecycleState state = s.getState();
if (LifecycleState.STOPPING_PREP.compareTo(state) <= 0
&& LifecycleState.DESTROYED.compareTo(state) >= 0) {
} else {
s.stop();
s.destroy();
}
} catch (LifecycleException e) {
log.error("Catalina.stop", e);
}
}
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# 小结
以上就是整个Tomcat的启动流程，其实就是用Bootstrap类的init、start、stop的这些方法，来代理
Catalina的这写方法进行相应的操作。所以说Tomcat的核心是Catalina，其中有一个小工具Digester 官网地址是
一个很有意思的工具，我们平时在工作中解析XML的时候可以考虑使用这个小工具。
