这个方法主要设置(这个方法很重要，贵在理解，虽然还没学过设计模式。。)
1、遇到<server>标签时创建StandardServer实例
设置StandardServer类内部的相关属性
并调用Catalina.setServer()方法设置server
2、遇到<Server>标签的子标签<Listener>==》对应匹配模式"Server/Listener"时
创建Listener实例，创建类名通过<Listener className=要创建的全类名(包名+类名)>获取属性className的值进行创建。
调用StandardServer的addLifecycleListener（）为server添加监听器
3、<Service>标签时即匹配模式为："Server/Service"创建StandardService实例，放入Stack栈中，调用addSetProperties方法为StandardService设置相关属性
digester.addSetNext("Server/Service",
"addService",
"org.apache.catalina.Service");
调用Service的parent=stack.peek(1)即Server对象的addService方法为与Server关联。
4、同2一样为Service设置监听器
5、<executor>标签时即匹配模式："Server/Service/Executor" 生成StandardThreadExecutor实例，
设置StandardThreadExecutor的属性
调用其父类Service的addExecutor方法与Service关联
6、调用addRule方法如上一样，
pattern："Server/Service/Connector"==>创建Connector实例，设置属性，调用StandardService.addConnector()。为Connector设置监听器
7、调用addRuleSet（）方法
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/"));
跟6一样
、、设置Engine
，EngineRuleSet(String prefix)当遇到模式为prefix + "Engine"即"Server/Service/Engine"会在EngineRuleSet.addRuleInstances（）内部调用
addObjectCreate、addSetProperties、addRule这三个方法创建StandardEngine实例，设置属性，调用Service。setContainer()方法。
创建SimpleTcpCluster实例调用Engine.setCluster（）方法
给Engine添加监听器，
创建realm对象实例，调用对应方法与Engine关联。
创建AccessLogValve日志对象（将日志输出到。txt文件），设置属性，与engine关联。
、、设置host
创建StandardHost，设置属性，设置监听器：HostConfig
调用Container。addChild（）在这里Container即与Engine相关联
、、设置context
创建StandardContext，设置属性，设置监听器：ContextConfig
调用Container。addChild（）在这里Container即与Host相关联
创建WebappLoader，与StandardContext关联
创建StandardManager，与StandardContext关联
创建store存储类，与StandardContext关联
创建StandardSessionIdGenerator，与StandardManager关联
创建ApplicationParameter，与StandardContext关联
创建realm对象实例,与StandardContext关联
创建StandardRoot,与StandardContext关联
context==》WebResourceRoot==StandardRoot设置
创建WebResourceSet,与StandardRoot关联
（WebResourceSet的实现类有WarResourceSet、JarResourceSet、JarWarResourceSet、DirResourceSet、FileResourceSet等）
主要设置StandardRoot的preResources、jarResources、postResources这三个变量的实例
创建ContextResourceLink，与StandardContext关联
创建AccessLogValve，与StandardContext关联
创建StandardJarScanner，与StandardContext关联
创建StandardJarScanFilter，与StandardJarScanner关联
创建LegacyCookieProcessor，与StandardContext关联
Note:上面已经说明完的具体对象被创建的整个过程，下面是对Digester的一些方法的理解。可以忽略！
protected Digester createStartDigester() { long t1=System.currentTimeMillis(); // Initialize the digester Digester digester = new Digester(); digester.setValidating(false); digester.setRulesValidation(true); HashMap<Class<?>, List<String>> fakeAttributes = new HashMap<>(); ArrayList<String> attrs = new ArrayList<>(); attrs.add("className"); fakeAttributes.put(Object.class, attrs); 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"})); digester.addSetNext("Server/Service/Connector", "addConnector", "org.apache.catalina.connector.Connector"); 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"); // 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); }
addObjectCreate（）//Add an "object create" rule for the specified parameters.增加对象创建规则.遇到起始标签的元素，初始化一个实例对象入栈
addSetProperties（）//Add a "set properties" rule for the specified parameters.增加设置属性规则.遇到某个属性名，使用setter来赋值
如
digester.addSetProperties("Server");
对应标签<Server port="8005" shutdown="SHUTDOWN">
遇到匹配模式为：Server。addSetProperties方法会反射调用StandardServer对象的setPort(int) 和setShutdown（String）两个方法设置属性
//Add a "set next" rule for the specified parameters.增加set next规则.遇到下一标签时的动作
即反射调用方法名为methodName的方法。
digester.addSetNext("Server",
"setServer",
"org.apache.catalina.Server");
当遇到<Server>标签的下一标签时被调用
addSetNext方法会调用SetNextRule.end()方法会调用这个当前top栈顶对象的parent父对象(栈顶对象的下一个元素)的setServer（）方法
当StandardServer对象入栈后，栈中已经存在Catalina对象===>在Catalina.load()方法中设置了
所以StandardServer的parent父对象是Catalina，即调用Catalina.setServer()方法设置server属性。
addRule：调用rule的begin 、body、end、finish方法来解析xml，入栈和出栈给对象赋值
addRuleSet：调用addRuleInstances来解析xml标签
addObjectCreate（pattern ，className ，attributeName）
1、
Add an "object create" rule for the specified parameters为指定的参数增加一个对象创建规则.
- Parameters:
- pattern Element matching pattern元素匹配模式
- className Default Java class name to be created要创建的java类的名字
- attributeName Attribute name that optionally overrides the default Java class name to be created属性名称可以覆盖要创建的默认Java类名称
- 获取xml文件中attributes属性名为：className所对应的值替换第二个参数
-
ObjectCreateRule.java类的begin(String namespace, String name, Attributes attributes)方法，
这个方法将通过类名加载Class然后调用class.newInstance()生成类实例，最后放入digest的对象栈顶digester.push(instance);
String realClassName = className; if (attributeName != null) { String value = attributes.getValue(attributeName); if (value != null) { realClassName = value; } }
这个addObjectCreate()方法又调用addRule（）方法
2、
Register a new Rule matching the specified pattern. This method sets the Digester property on the rule.
- Parameters:
- pattern Element matching pattern
- rule Rule to be registered这里的rule使用的是ObjectCreateRule
public void addRule(String pattern, Rule rule) {
rule.setDigester(this);设置digester，将保存创建的对象的实例
getRules().add(pattern, rule);这里将会返回Rules接口的实现类。然后再调用Rules.add()来添加Rule实例
}
Note:Rules：是一个接口public interface Rules
公共接口定义规则实例的集合（和相应的匹配模式）以及匹配策略的实现，
该策略选择与解析期间发现的嵌套元素的特定模式匹配的规则。
Rule：是一个抽象类public abstract class Rule
ObjectCreateRule类的解释
Rule implementation that creates a new object and pushes it onto the object stack. When the element is complete, the object will be popped
Rule实现类，创建一个新对象并将其推送到对象堆栈上。当元素完成时，对象将被弹出
3、RuleBase.add(pattern, rule)
public void add(String pattern, Rule rule) {
// to help users who accidently add '/' to the end of their patterns
int patternLength = pattern.length();
if (patternLength>1 && pattern.endsWith("/")) {
pattern = pattern.substring(0, patternLength-1);
}
List<Rule> list = cache.get(pattern);
if (list == null) {
list = new ArrayList<>();
cache.put(pattern, list);
}
list.add(rule);
rules.add(rule);
if (this.digester != null) {
rule.setDigester(this.digester);
}
if (this.namespaceURI != null) {
rule.setNamespaceURI(this.namespaceURI);
}
}
上面方法用用HashMap<String, List<Rule>>类型变量cache存放pattern和Rule集合，用rules集合存放新加入的规则rules.add（rule）
注：
只有当遇到改元素的结束标签时才会将改标签代表的对象实例弹出栈。