Tommcat源碼學習（四）--Tomcat_7.0.70 server.xml文件的加載與解析
一、文件的加載
Bootstrap的load方法是加載Tomcat的server.xml的入口，load方法實際經過反射調用catalinaDaemon（類型爲Catalina）的load方法：java
/**
* Load daemon.
*/
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);//經過反射機制調用Catalina類的load方法。
if (log.isDebugEnabled())
log.debug("Calling startup class " + method);
method.invoke(catalinaDaemon, param);
}
Catalina類的load方法：express
/*
* Load using arguments
*/
public void load(String args[]) {
try {
if (arguments(args)) {
load();//調用自身的load方法
}
} catch (Exception e) {
e.printStackTrace(System.out);
}
}
/**
* Start a new server instance.
*/
public void load() {
long t1 = System.nanoTime();
initDirs(); //用於對catalina.home和catalina.base的一些檢查工做
// Before digester - it may be needed
initNaming();//給系統設置java.naming.factory.url.pkgs和java.naming.factory.initial
// Create and execute our Digester
Digester digester = createStartDigester();//實例化Digester
InputSource inputSource = null;
InputStream inputStream = null;
File file = null;
try {
try {
file = configFile();//獲取conf/server.xml配置文件
inputStream = new FileInputStream(file);獲取conf/server.xml配置文件輸入流
inputSource = new InputSource(file.toURI().toURL().toString());
} catch (Exception e) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("catalina.configFail", file), e);
}
}
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);
}
}
}
// This should be included in catalina.jar
// Alternative: don't bother with xml, just create it manually.
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);//將FileInputStream封裝爲InputSource
digester.push(this);
digester.parse(inputSource);//調用Digester的parse方法進行解析
} 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
}
}
}
getServer().setCatalina(this);
// Stream redirection
initStreams();//initStreams對輸出流、錯誤流重定向
// Start the new server
try {
getServer().init();//初始化server
} 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");
}
}
下面開始分析整個過程：apache
1.一、initDirs（）方法用於對catalina.home和catalina.base的一些檢查工做
protected void initDirs() {
String catalinaHome = System.getProperty(Globals.CATALINA_HOME_PROP);
if (catalinaHome == null) {
// Backwards compatibility patch for J2EE RI 1.3
String j2eeHome = System.getProperty("com.sun.enterprise.home");
if (j2eeHome != null) {
catalinaHome=System.getProperty("com.sun.enterprise.home");
} else if (System.getProperty(Globals.CATALINA_BASE_PROP) != null) {
catalinaHome = System.getProperty(Globals.CATALINA_BASE_PROP);
}
}
// last resort - for minimal/embedded cases.
if(catalinaHome==null) {
catalinaHome=System.getProperty("user.dir");
}
if (catalinaHome != null) {
File home = new File(catalinaHome);
if (!home.isAbsolute()) {
try {
catalinaHome = home.getCanonicalPath();
} catch (IOException e) {
catalinaHome = home.getAbsolutePath();
}
}
System.setProperty(Globals.CATALINA_HOME_PROP, catalinaHome);
}
if (System.getProperty(Globals.CATALINA_BASE_PROP) == null) {
System.setProperty(Globals.CATALINA_BASE_PROP,
catalinaHome);
} else {
String catalinaBase = System.getProperty(Globals.CATALINA_BASE_PROP);
File base = new File(catalinaBase);
if (!base.isAbsolute()) {
try {
catalinaBase = base.getCanonicalPath();
} catch (IOException e) {
catalinaBase = base.getAbsolutePath();
}
}
System.setProperty(Globals.CATALINA_BASE_PROP, catalinaBase);
}
String temp = System.getProperty("java.io.tmpdir");
if (temp == null || (!(new File(temp)).exists())
|| (!(new File(temp)).isDirectory())) {
log.error(sm.getString("embedded.notmp", temp));
}
}
1.二、initNaming()方法給系統設置java.naming.factory.url.pkgs和java.naming.factory.initial
protected void initNaming() {
// Setting additional variables
if (!useNaming) {
log.info( "Catalina naming disabled");
System.setProperty("catalina.useNaming", "false");
} else {
System.setProperty("catalina.useNaming", "true");
String value = "org.apache.naming";
String oldValue =
System.getProperty(javax.naming.Context.URL_PKG_PREFIXES);
if (oldValue != null) {
value = value + ":" + oldValue;
}
System.setProperty(javax.naming.Context.URL_PKG_PREFIXES, value);
if( log.isDebugEnabled() ) {
log.debug("Setting naming prefix=" + value);
}
value = System.getProperty
(javax.naming.Context.INITIAL_CONTEXT_FACTORY);
if (value == null) {
System.setProperty
(javax.naming.Context.INITIAL_CONTEXT_FACTORY,
"org.apache.naming.java.javaURLContextFactory");
} else {
log.debug( "INITIAL_CONTEXT_FACTORY already set " + value );
}
}
}
在建立JNDI上下文時，使用Context.INITIAL _ CONTEXT _ FACTORY（"java.naming.factory.initial"）屬性，來指定建立JNDI上下文的工廠類；Context.URL _ PKG _ PREFIXES("java.naming.factory.url.pkgs")用在查詢url中包括scheme方法id時建立對應的JNDI上下文.tomcat
1.三、createStartDigester()建立並配置將要用來啓動的Digester實例，而且設置一些列Rule，具體映射到server.xml
/**
* Create and configure the Digester we will be using for startup.
*/
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<Class<?>, List<String>>();
ArrayList<String> attrs = new ArrayList<String>();
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.NamingResources");
digester.addSetProperties("Server/GlobalNamingResources");
digester.addSetNext("Server/GlobalNamingResources",
"setGlobalNamingResources",
"org.apache.catalina.deploy.NamingResources");
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);
}
從上面的代碼能夠看出：首先建立Digester，Digester繼承了DefaultHandler，而DefaultHandler默認實現了ContentHander、DTDHander、ErrorHandler及EntityResolver 這4個接口，代碼以下：數據結構
public class DefaultHandler implements EntityResolver, DTDHandler, ContentHandler, ErrorHandler
經過源碼能夠發現DefaultHandler的全部實現都是空實現，因此解析還須要Digester。（具體分析後面在說）。app
1.四、configFile()獲取配置文件conf/server.xml，並使用FileInputStream獲取conf/server.xml配置文件輸入流
/**
* Return a File object representing our configuration file.
*/
protected File configFile() {
File file = new File(configFile);
if (!file.isAbsolute()) {
file = new File(System.getProperty(Globals.CATALINA_BASE_PROP), configFile);
}
return (file);
}
1.五、將FileInputStream封裝爲InputSource，而且調用Digester的parse方法進行解析
inputSource.setByteStream(inputStream); digester.push(this); digester.parse(inputSource);
1.六、initStreams()對輸出流、錯誤流重定向
protected void initStreams() {
// Replace System.out and System.err with a custom PrintStream
System.setOut(new SystemLogHandler(System.out));
System.setErr(new SystemLogHandler(System.err));
}
1.七、初始化server
// Start the new 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("Catalina.start", e);
}
}
二、文件的解析
當加載server.xml配置文件到內存後，開始對XML文件中的內容進行解析，主要包含兩個步驟：ide
- 構造server.xml的規則，這些規則便可以用於構造Tomcat內部的容器（如StandardServer，StandardService等），也能夠對server.xml進行合法性檢查。若是server.xml不符合Tomcat內置的規則，在解析時將拋出異常，進而致使Tomcat沒法啓動。
- 使用SAX解析server.xml，邊解析邊應用規則，最終使用server.xml中的配置構建好Tomcat所需的各類容器。
Tomcat將server.xml文件中的全部元素上的屬性都抽象爲Rule，以Server元素爲例，在內存中對應Server實例，Server實例的屬性值就來自於Server元素的屬性值。經過對規則（Rule）的應用，最終改變Server實例的屬性值。Rule是一個抽象類，其中定義瞭如下方法：ui
- getDigester：獲取Digester實例；
- setDigester：設置Digester實例；
- getNamespaceURI：獲取Rule所在的相對命名空間URI；
- setNamespaceURI：設置Rule所在的相對命名空間URI；
- begin(String namespace, String name, Attributes attributes)：此方法在遇到一個匹配的XML元素的開頭時被調用，如<Server>；
- body(String namespace, String name, String text)：在遇到匹配XML元素的body時，此方法被調用，如進入標籤內部時；
- end(String namespace, String name)：此方法在遇到一個匹配的XML元素的末尾時被調用。如：< /Server>；
Rule目前有不少實現類，如：NodeCreateRule、AbsoluteOrderingRule、CallParamRule、ConnectorCreateRule等。下圖展現了Rule的部分實現類：this
Tomcat使用SAX（Simple API for XML)解析XML:url
SAX解析XML採用的是從上而下的基於事件驅動的解析方式，在解析過程當中會視狀況自動調用ContentHandler接口中的startDocument()、startElement()、characters()、endElement()、endDocument()等相關的方法。
由編譯執行的結果分析：
- startDocument()方法只會在文檔開始解析的時候被調用，每次解析只會調用一次。
- startElement()方法每次在開始解析一個元素，即遇到元素標籤開始的時候都會調用。
- characters()方法也是在每次解析到元素標籤攜帶的內容時都會調用，即便該元素標籤的內容爲空或換行。並且若是元素內嵌套元素，在父元素結束標籤前， characters()方法會再次被調用，此處須要注意。
- endElement()方法每次在結束解析一個元素，即遇到元素標籤結束的時候都會調用。
- endDocument()方法只會在文檔解析結束的時候被調用，每次解析只會調用一次。
使用SAX解析XML的好處：
- SAX 不用解析完整個文檔
- 相比於 DOM 而言 SAX 是一種速度更快，更有效，佔用內存更少的解析 XML 文件的方法
- 逐行掃描，能夠作到邊掃描邊解析，所以 SAX 能夠在解析文檔的任意時刻中止解析
因爲SAX是基於事件驅動的，不用解析完整個文檔，在按內容順序解析文檔過程當中， SAX 會判斷當前讀到的字符是否符合 XML 文件語法中的某部分。若是符合某部分，則會觸發事件。所謂觸發事件，就是調用一些回調方法。在用 SAX 解析 xml 文檔時候，在讀取到文檔開始和結束標籤時候就會回調一個事件，在讀取到其餘節點與內容時候也會回調一個事件。在 SAX 接口中，事件源是 org.xml.sax 包中的 XMLReader ，它經過 parser() 方法來解析 XML 文檔，併產生事件。事件處理器是 org.xml.sax 包中 ContentHander 、 DTDHander 、 ErrorHandler ，以及 EntityResolver 這4個接口：
- ContentHander （ XML 文檔的開始與結束）setContentHandler(ContentHandler h)
- DTDHander （ 處理 DTD 解析） setDTDHandler(DTDHandler h)
- ErrorHandler （ 處理 XML 時產生的錯誤）setErrorHandler(ErrorHandler h)
- EntityResolver （處理外部實體） setEntityResolver(EntityResolver e)
回調方法通常都定義在ContentHandler接口中，上面已經對這些回調方法的加載順序已經說了就不在介紹了。
使用 SAX 解析 XML 文件通常有如下五個步驟：
- 建立一個 SAXParserFactory 對象；
- 調用 SAXParserFactory 中的 newSAXParser 方法建立一個 SAXParser 對象；
- 而後在調用 SAXParser 中的 getXMLReader 方法獲取一個 XMLReader 對象；
- 實例化一個 DefaultHandler 對象；
- 鏈接事件源對象 XMLReader 到事件處理類 DefaultHandler 中；
- 調用 XMLReader 的 parse 方法從輸入源中獲取到的 xml 數據；
- 經過 DefaultHandler 返回咱們須要的數據集合。
咱們經過源碼能夠發現DefaultHandler的全部實現都是空實現，因此解析還須要Digester自身，代碼以下：
@Override
public void startDocument() throws SAXException {
if (saxLog.isDebugEnabled()) {
saxLog.debug("startDocument()");
}
// ensure that the digester is properly configured, as
// the digester could be used as a SAX ContentHandler
// rather than via the parse() methods.
configure();
}
@Override
public void startElement(String namespaceURI, String localName,
String qName, Attributes list)
throws SAXException {
boolean debug = log.isDebugEnabled();
if (saxLog.isDebugEnabled()) {
saxLog.debug("startElement(" + namespaceURI + "," + localName + "," +
qName + ")");
}
// Parse system properties
list = updateAttributes(list);
// Save the body text accumulated for our surrounding element
bodyTexts.push(bodyText);
bodyText = new StringBuilder();
// the actual element name is either in localName or qName, depending
// on whether the parser is namespace aware
String name = localName;
if ((name == null) || (name.length() < 1)) {
name = qName;
}
// Compute the current matching rule
StringBuilder sb = new StringBuilder(match);
if (match.length() > 0) {
sb.append('/');
}
sb.append(name);
match = sb.toString();
if (debug) {
log.debug(" New match='" + match + "'");
}
// Fire "begin" events for all relevant rules
List<Rule> rules = getRules().match(namespaceURI, match);
matches.push(rules);
if ((rules != null) && (rules.size() > 0)) {
for (int i = 0; i < rules.size(); i++) {
try {
Rule rule = rules.get(i);
if (debug) {
log.debug(" Fire begin() for " + rule);
}
rule.begin(namespaceURI, name, list);
} catch (Exception e) {
log.error("Begin event threw exception", e);
throw createSAXException(e);
} catch (Error e) {
log.error("Begin event threw error", e);
throw e;
}
}
} else {
if (debug) {
log.debug(" No rules found matching '" + match + "'.");
}
}
}
@Override
public void endDocument() throws SAXException {
if (saxLog.isDebugEnabled()) {
if (getCount() > 1) {
saxLog.debug("endDocument(): " + getCount() +
" elements left");
} else {
saxLog.debug("endDocument()");
}
}
while (getCount() > 1) {
pop();
}
// Fire "finish" events for all defined rules
Iterator<Rule> rules = getRules().rules().iterator();
while (rules.hasNext()) {
Rule rule = rules.next();
try {
rule.finish();
} catch (Exception e) {
log.error("Finish event threw exception", e);
throw createSAXException(e);
} catch (Error e) {
log.error("Finish event threw error", e);
throw e;
}
}
// Perform final cleanup
clear();
}
@Override
public void endElement(String namespaceURI, String localName,
String qName) throws SAXException {
boolean debug = log.isDebugEnabled();
if (debug) {
if (saxLog.isDebugEnabled()) {
saxLog.debug("endElement(" + namespaceURI + "," + localName +
"," + qName + ")");
}
log.debug(" match='" + match + "'");
log.debug(" bodyText='" + bodyText + "'");
}
// Parse system properties
bodyText = updateBodyText(bodyText);
// the actual element name is either in localName or qName, depending
// on whether the parser is namespace aware
String name = localName;
if ((name == null) || (name.length() < 1)) {
name = qName;
}
// Fire "body" events for all relevant rules
List<Rule> rules = matches.pop();
if ((rules != null) && (rules.size() > 0)) {
String bodyText = this.bodyText.toString();
for (int i = 0; i < rules.size(); i++) {
try {
Rule rule = rules.get(i);
if (debug) {
log.debug(" Fire body() for " + rule);
}
rule.body(namespaceURI, name, bodyText);
} catch (Exception e) {
log.error("Body event threw exception", e);
throw createSAXException(e);
} catch (Error e) {
log.error("Body event threw error", e);
throw e;
}
}
} else {
if (debug) {
log.debug(" No rules found matching '" + match + "'.");
}
if (rulesValidation) {
log.warn(" No rules found matching '" + match + "'.");
}
}
// Recover the body text from the surrounding element
bodyText = bodyTexts.pop();
// Fire "end" events for all relevant rules in reverse order
if (rules != null) {
for (int i = 0; i < rules.size(); i++) {
int j = (rules.size() - i) - 1;
try {
Rule rule = rules.get(j);
if (debug) {
log.debug(" Fire end() for " + rule);
}
rule.end(namespaceURI, name);
} catch (Exception e) {
log.error("End event threw exception", e);
throw createSAXException(e);
} catch (Error e) {
log.error("End event threw error", e);
throw e;
}
}
}
// Recover the previous match expression
int slash = match.lastIndexOf('/');
if (slash >= 0) {
match = match.substring(0, slash);
} else {
match = "";
}
}
當咱們建立好Digester後，會調用addObjectCreate、addSetProperties、addSetNext方法陸續添加不少Rule，這些方法的實現如代碼：
public void addObjectCreate(String pattern, String className,
String attributeName) {
addRule(pattern,
new ObjectCreateRule(className, attributeName));
}
public void addSetProperties(String pattern) {
addRule(pattern,
new SetPropertiesRule());
}
public void addSetNext(String pattern, String methodName,
String paramType) {
addRule(pattern,
new SetNextRule(methodName, paramType));
}
這三個方法分別建立ObjectCreateRule、SetPropertiesRule及SetNextRule，爲了便於理解，咱們舉例說明(Server標籤)：
digester.addObjectCreate("Server","org.apache.catalina.core.StandardServer","className");
digester.addSetProperties("Server");
digester.addSetNext("Server","setServer", "org.apache.catalina.Server");
咱們知道最終會建立ObjectCreateRule、SetPropertiesRule及SetNextRule，而且調用addRule方法。
public void addRule(String pattern, Rule rule) {
rule.setDigester(this);
getRules().add(pattern, rule);
}
從代碼能夠看出，addRule方法首先調用getRules方法獲取RulesBase，而後調用RulesBase的add方法。代碼以下：
//getRules()獲取RulesBase
public Rules getRules() {
if (this.rules == null) {
this.rules = new RulesBase();
this.rules.setDigester(this);
}
return (this.rules);
}
//RulesBase的add方法
@Override
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<Rule>();
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);
}
}
其中，cache的數據結構爲HashMap<String,List<Rule>>，每一個鍵值維護一個List<Rule>，由此可知，對Server標籤來講，對應的Rule列表爲ObjectCreateRule、SetPropertiesRule及SetNextRule。
Digester解析XML的入口是其parse方法，其處理步驟以下：
1.建立XMLReader ；
2.使用XMLReader解析XML。
public Object parse(InputSource input) throws IOException, SAXException {
configure();
getXMLReader().parse(input);
return (root);
}
//configure()
protected void configure() {
// Do not configure more than once
if (configured) {
return;
}
log = LogFactory.getLog("org.apache.tomcat.util.digester.Digester");
saxLog = LogFactory.getLog("org.apache.tomcat.util.digester.Digester.sax");
// Perform lazy configuration as needed
initialize(); // call hook method for subclasses that want to be initialized once only
// Nothing else required by default
// Set the configuration flag to avoid repeating
configured = true;
}
getXMLReader方法調用getParser建立SAXParser ，而後調用SAXParser 的getXMLReader方法建立XMLReader.
public XMLReader getXMLReader() throws SAXException {
if (reader == null){
reader = getParser().getXMLReader();
}
reader.setDTDHandler(this);
reader.setContentHandler(this);
if (entityResolver == null){
reader.setEntityResolver(this);
} else {
reader.setEntityResolver(entityResolver);
}
reader.setProperty(
"http://xml.org/sax/properties/lexical-handler", this);
reader.setErrorHandler(this);
return reader;
}
getParser方法調用getFactory方法建立SAXParserFactory，而後調用SAXParserFactory的newSAXParser方法建立SAXParser
public SAXParser getParser() {
// Return the parser we already created (if any)
if (parser != null) {
return (parser);
}
// Create a new parser
try {
parser = getFactory().newSAXParser();
} catch (Exception e) {
log.error("Digester.getParser: ", e);
return (null);
}
return (parser);
}
getFactory方法使用SAX的API生成SAXParserFactory實例.
public SAXParserFactory getFactory() throws SAXNotRecognizedException, SAXNotSupportedException,ParserConfigurationException {
if (factory == null) {
factory = SAXParserFactory.newInstance();
factory.setNamespaceAware(namespaceAware);
// Preserve xmlns attributes
if (namespaceAware) {
factory.setFeature(
"http://xml.org/sax/features/namespace-prefixes",
true);
}
factory.setValidating(validating);
if (validating) {
// Enable DTD validation
factory.setFeature(
"http://xml.org/sax/features/validation",
true);
// Enable schema validation
factory.setFeature(
"http://apache.org/xml/features/validation/schema",
true);
}
}
return (factory);
}
XMLReader解析XML時，會生成事件，回調Digester的startDocument方法，解析的第一個元素是Server，此時回調Digester的startElement方法，入參Attributes list即Server上的屬性，如port、shutdown等，入參qName即爲Server.
@Override
public void startElement(String namespaceURI, String localName,
String qName, Attributes list)
throws SAXException {
boolean debug = log.isDebugEnabled();
if (saxLog.isDebugEnabled()) {
saxLog.debug("startElement(" + namespaceURI + "," + localName + "," +
qName + ")");
}
// Parse system properties
list = updateAttributes(list);
// Save the body text accumulated for our surrounding element
bodyTexts.push(bodyText);
bodyText = new StringBuilder();
// the actual element name is either in localName or qName, depending
// on whether the parser is namespace aware
String name = localName;
if ((name == null) || (name.length() < 1)) {
name = qName;
}
// Compute the current matching rule
StringBuilder sb = new StringBuilder(match);
if (match.length() > 0) {
sb.append('/');
}
sb.append(name);
match = sb.toString();
if (debug) {
log.debug(" New match='" + match + "'");
}
// Fire "begin" events for all relevant rules
List<Rule> rules = getRules().match(namespaceURI, match);
matches.push(rules);
if ((rules != null) && (rules.size() > 0)) {
for (int i = 0; i < rules.size(); i++) {
try {
Rule rule = rules.get(i);
if (debug) {
log.debug(" Fire begin() for " + rule);
}
rule.begin(namespaceURI, name, list);
} catch (Exception e) {
log.error("Begin event threw exception", e);
throw createSAXException(e);
} catch (Error e) {
log.error("Begin event threw error", e);
throw e;
}
}
} else {
if (debug) {
log.debug(" No rules found matching '" + match + "'.");
}
}
}
startElement方法的處理步驟以下：
1.match剛開始爲空字符串，拼接Server後變爲Server。
2.調用RulesBase的match方法，返回cache中按照鍵值Server匹配的ObjectCreateRule、SetPropertiesRule及SetNextRule。
3.循環列表依次遍歷ObjectCreateRule、SetPropertiesRule及SetNextRule，並調用它們的begin方法。
ObjectCreateRule的begin方法將生成Server的實例（默認爲"org.apache.catalina.core.StandardServer"，用戶能夠經過給Server標籤指定className使用其它Server實現），最後將Server的實例壓入Digester的棧中.
@Override
public void begin(String namespace, String name, Attributes attributes)
throws Exception {
// Identify the name of the class to instantiate
String realClassName = className;
if (attributeName != null) {
String value = attributes.getValue(attributeName);
if (value != null) {
realClassName = value;
}
}
if (digester.log.isDebugEnabled()) {
digester.log.debug("[ObjectCreateRule]{" + digester.match +
"}New " + realClassName);
}
if (realClassName == null) {
throw new NullPointerException("No class name specified for " +
namespace + " " + name);
}
// Instantiate the new object and push it on the context stack
Class<?> clazz = digester.getClassLoader().loadClass(realClassName);
Object instance = clazz.newInstance();
digester.push(instance);
}
SetPropertiesRule的begin方法首先將剛纔壓入棧中的Server實例出棧，而後給Server實例設置各個屬性值，如port、shutdown等:
@Override
public void begin(String namespace, String theName, Attributes attributes)
throws Exception {
// Populate the corresponding properties of the top object
Object top = digester.peek();
if (digester.log.isDebugEnabled()) {
if (top != null) {
digester.log.debug("[SetPropertiesRule]{" + digester.match +
"} Set " + top.getClass().getName() +
" properties");
} else {
digester.log.debug("[SetPropertiesRule]{" + digester.match +
"} Set NULL properties");
}
}
// set up variables for custom names mappings
int attNamesLength = 0;
if (attributeNames != null) {
attNamesLength = attributeNames.length;
}
int propNamesLength = 0;
if (propertyNames != null) {
propNamesLength = propertyNames.length;
}
for (int i = 0; i < attributes.getLength(); i++) {
String name = attributes.getLocalName(i);
if ("".equals(name)) {
name = attributes.getQName(i);
}
String value = attributes.getValue(i);
// we'll now check for custom mappings
for (int n = 0; n<attNamesLength; n++) {
if (name.equals(attributeNames[n])) {
if (n < propNamesLength) {
// set this to value from list
name = propertyNames[n];
} else {
// set name to null
// we'll check for this later
name = null;
}
break;
}
}
if (digester.log.isDebugEnabled()) {
digester.log.debug("[SetPropertiesRule]{" + digester.match +
"} Setting property '" + name + "' to '" +
value + "'");
}
if (!digester.isFakeAttribute(top, name)
&& !IntrospectionUtils.setProperty(top, name, value)
&& digester.getRulesValidation()) {
digester.log.warn("[SetPropertiesRule]{" + digester.match +
"} Setting property '" + name + "' to '" +
value + "' did not find a matching property.");
}
}
}
SetNextRule的begin不作什麼動做。當遇到Server的結束標籤時，還會依次調用ObjectCreateRule、SetPropertiesRule及SetNextRule的end方法，再也不贅述。全部元素的解析都與Server標籤同理，最終將server.xml文件中設置的元素及其屬性值，構造出tomcat中的容器，如：Server、Service、Connector等.
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