How tomcat work 之 第十五章之Digester之ContextConfig之the defaultConfig Method

the defaultConfig Method

defaultConfig方法读取和解析默认的web.xml文件，这个文件在CATALINA_HOME/conf目录下。其代码清单如15.13所示：

private void defaultConfig() {         // Open the default web.xml file, if it exists         File file = new File(Constants.DefaultWebXml);         if (!file.isAbsolute())              file = new File(System.getProperty("catalina.base"),Constants.DefaultWebXml);          FileInputStream stream = null;          try{                stream = new FileInputStream(file.getCanonicalPath());                 stream.close();                 stream = null;               }               catch (FileNotFoundException e) {             log(sm.getString("contextConfig.defaultMissing"));             return;        }         catch (IOException e) {              log(sm.getString("contextConfig.defaultMissing"), e);              return;          }          // Process the default web.xml file          synchronized (webDigester) {              try {                       InputSource is =new InputSource("file://" + file.getAbsolutePath());                       stream = new FileInputStream(file);                        is.setByteStream(stream);                        webDigester.setDebug(getDebug());                         if (context instanceof StandardContext)                             ((StandardContext) context).setReplaceWelcomeFiles(true);                          webDigester.clear();                          webDigester.push(context);                          webDigester.parse(is);          catch (SAXParseException e) {                    log(sm.getString("contextConfig.defaultParse"), e);                    log(sm.getString("contextConfig.defaultPosition","" + e.getLineNumber(), "" + e.getColumnNumber()));                    ok = false;                 }          catch (Exception e) {                log(sm.getString("contextConfig.defaultParse"), e);                ok = false;          }          finally {                    try {                           if (stream != null) {                                     stream.close();                             }                        }                    catch (IOException e) {                            log(sm.getString("contextConfig.defaultClose"), e);                    }                }          }  }

defaultConfig方法首先创建一个与default.xml文件相关联的文件对象。

File file = new File(Constants.DefaultWebXml);

DefaultWebXML的值是在一个常量类中定义：

public static final String DefaultWebXml = "conf/web.xml";

defaultConfig方法稍后处理web.xml文件。其持有webDigester的内部锁，之后解析文件：

synchronized (webDigester) {      try {         InputSource is =            new InputSource("file://" + file.getAbsolutePath());         stream = new FileInputStream(file);          is.setByteStream(stream);         webDigester.setDebug(getDebug());         if (context instanceof StandardContext)             ((StandardContext) context).setReplaceWelcomeFiles(true);         webDigester.clear();         webDigester.push(context);         webDigester.parse(is);

与Digester实例关联的webDigester对象已经设置了处理web.xml文件的规则。这会在稍后的章节中讲解。

the applicationConfig method

这个方法与defaultConfig方法相似，除了它处理的是应用部署描述符。部署描述符位于应用程序目录的WEB-INF目录下。

private void applicationConfig() {    // Open the application web.xml file, if it exists    InputStream stream = null;    ServletContext servletContext = context.getServletContext();     if (servletContext != null)         stream = servletContext.getResourceAsStream(Constants.ApplicationWebXml);     if (stream == null) {         log(sm.getString("contextConfig.applicationMissing"));         return;     }     // Process the application web.xml file     synchronized (webDigester) {         try {              URL url =                  servletContext.getResource(Constants.ApplicationWebXml);                             InputSource is = new InputSource(url.toExternalForm());              is.setByteStream(stream);              webDigester.setDebug(getDebug());              if (context instanceof StandardContext) {                   ((StandardContext) context).setReplaceWelcomeFiles(true);              }              webDigester.clear();              webDigester.push(context);              webDigester.parse(is);           }           catch (SAXParseException e) {              log(sm.getString("contextConfig.applicationParse"), e);              log(sm.getString("contextConfig.applicationPosition","" + e.getLineNumber(),"" + e.getColumnNumber()));              ok = false;         }         catch (Exception e) {             log(sm.getString("contextConfig.applicationParse"), e);             ok = false;         }         finally {              try {                  if (stream != null){                       stream.close();                   }              }              catch (IOException e) {                 log(sm.getString("contextConfig.applicationClose"),e);              }            }          }      }      

create Web Digester

一个Digester对象引用，叫做webDigester，存在于ContextConfig类中：

private static Digester webDigester = createWebDigester();

Digester用于解析默认的web.xml和应用程序中的web.xml文件。当调用createWebDigester方式时，添加处理web.xml文件的规则。其代码清单如下：

private static Digester createWebDigester() {    URL url = null;    Digester webDigester = new Digester();    webDigester.setValidating(true);    url = ContextConfig.class.getResource(Constants.WebDtdResourcePath_22);    webDigester.register(Constants.WebDtdPublicId_22,url.toString());    url = ContextConfig.class.getResource(Constants.WebDtdResourcePath_23);    webDigester.register(Constants.WebDtdPublicId_23,url.toString());    url.toString());    webDigester.addRuleSet(new WebRuleSet());    return (webDigester);}         

注意 createWebDigester方法调用了webDigester的addRuleSet方法，来解析WebRuleSet的一个实例。WebRuleSet是RuleSetBase的一个子类。如果熟悉一个Servlet应用程序的部署描述符的语法并且阅读了这章开头的Digester部分，你应该能够理解其实如何工作的。

WebRuleSet的代码清单如下。注意为了节省空间，移除了addRuleInstance部分。

package org.apache.catalina.startup;import java.lang.reflect.Method;import org.apache.catalina.Context;import org.apache.catalina.Wrapper;import org.apache.catalina.deploy.SecurityConstraint;import org.apache.commons.digester.Digester;import org.apache.commons.digester.Rule;import org.apache.commons.digester.RuleSetBase;import org.xml.sax.Attributes;public class WebRuleSet extends RuleSetBase {    protected String prefix = null;    public WebRuleSet () {        this("");    }    public WebRuleSet(String prefix) {        super();        this.namespaceURI = null;        this.prefix = prefix;    }    public void addRuleInstances(Digester digester) {        digester.addRule(prefix + "web-app",new SetPublicIdRule(digester, "setPublicId"));        digester.addCallMethod(prefix + "web-app/context-param","addParameter", 2);        digester.addCallParam(prefix +"web-app/context-param/param-name", 0);         digester.addCallParam(prefix +"web-app/context-param/param-value", 1);         digester.addCallMethod(prefix + "web-app/display-name","setDisplayName", 0);        digester.addRule(prefix + "web-app/distributable",new SetDistributableRule(digester));        ...        digester.addObjectCreate(prefix + "web-app/filter","org.apache.catalina.deploy.FilterDef");        digester.addSetNext(prefix + "web-app/filter", "addFilterDef","org.apache.catalina.deploy.FilterDef");        digester.addCallMethod(prefix + "web-app/filter/description","setDescription", 0);        digester.addCallMethod(prefix + "web-app/filter/display-name",  "setDisplayName", 0);        digester.addCallMethod(prefix + "web-app/filter/filter-class","setFilterClass", 0);        digester.addCallMethod(prefix + "web-app/filter/filter-name","setFilterName", 0);        digester.addCallMethod(prefix + "web-app/filter/large-icon","setLargeIcon", 0);        digester.addCallMethod(prefix + "web-app/filter/small-icon","setSmallIcon", 0);        digester.addCallMethod(prefix + "web-app/filter/init-param","addInitParameter", 2);        digester.addCallParam(prefix +"web-app/filter/init-param/param-name", 0);        digester.addCallParam(prefix +"web-app/filter/init-param/param-value", 1);        digester.addObjectCreate(prefix + "web-app/filter-mapping","org.apache.catalina.deploy.FilterMap");        digester.addSetNext(prefix + "web-app/filter-mapping","addFilterMap", "org.apache.catalina.deploy.FilterMap");        digester.addCallMethod(prefix +"web-app/filter-mapping/filter-name", "setFilterName", 0);        digester.addCallMethod(prefix +"web-app/filter-mapping/servlet-name", "setServletName", 0);        digester.addCallMethod(prefix +"web-app/filter-mapping/url-pattern", "setURLPattern", 0);        digester.addCallMethod (prefix +"web-app/listener/listener-class", "addApplicationListener", 0);        ...        digester.addRule(prefix + "web-app/servlet",new WrapperCreateRule(digester));        digester.addSetNext(prefix + "web-app/servlet","addChild", "org.apache.catalina.Container");        digester.addCallMethod(prefix + "web-app/servlet/init-param","addInitParameter", 2);        digester.addCallParam(prefix +"web-app/servlet/init-param/param-name", 0);        digester.addCallParam(prefix +"web-app/servlet/init-param/param-value", 1);        digester.addCallMethod(prefix + "web-app/servlet/jsp-file","setJspFile", 0);        digester.addCallMethod(prefix +"web-app/servlet/load-on-startup", "setLoadOnStartupString", 0);        digester.addCallMethod(prefix +"web-app/servlet/run-as/role-name", "setRunAs", 0);        digester.addCallMethod(prefix +"web-app/servlet/security-role-ref", "addSecurityReference", 2);        digester.addCallParam(prefix +"web-app/servlet/security-role-ref/role-link", 1);        digester.addCallParam(prefix +"web-app/servlet/security-role-ref/role-name", 0);        digester.addCallMethod(prefix + "web-app/servlet/servlet-class","setServletdass", 0);        digester.addCallMethod(prefix + "web-app/servlet/servlet-name","setName", 0);        digester.addCallMethod(prefix + "web-app/servlet-mapping","addServletMapping", 2);        digester.addCallParam(prefix +"web-app/servlet-mapping/servlet-name"/ 1);        digester.addCallParam(prefix +"web-app/servlet-mapping/url-pattern", 0);        digester.addCallMethod (prefix +"web-app/session-config/session-timeout", "setSessionTimeout", 1,new Class[] { Integer.TYPE });        digester.addCallParam(prefix +"web-app/session-config/session-timeout", 0);        digester.addCallMethod(prefix + "web-app/taglib","addTaglib", 2);        digester.addCallParam(prefix + "web-app/taglib/taglib-location",1);        digester.addCallParam(prefix + "web-app/taglib/taglib-uri", 0);        digester.addCallMethod(prefix +"web-app/welcome-file-list/welcome-file", "addWelcomeFile", 0);        }     } // --------------------------------------------- Private Classes  final class SetAuthConstraintRule extends Rule {      public SetAuthConstraintRule(Digester digester) {          super(digester);      }      public void begin(Attributes attributes) throws Exception {          SecurityConstraint securityConstraint = (SecurityConstraint) digester.peek();          securityConstraint.setAuthConstraint(true);           if (digester.getDebug() > 0)               digester.log("Calling SecurityConstraint.setAuthConstraint(true)");    }}...final class WrapperCreateRule extends Rule {    public WrapperCreateRule(Digester digester) {         super(digester);    }    public void begin(Attributes attributes) throws Exception {        Context context =(Context) digester.peek(digester.getCount() - 1);         Wrapper wrapper = context.createWrapper();            digester.push(wrapper);          if (digester.getDebug() > 0)              digester.log("new " + wrapper.getClass().getName()); }public void end() throws Exception {    Wrapper wrapper = (Wrapper) digester.pop();     if (digester.getDebug() > 0)         digester.log("pop " + wrapper.getclass().getName());  }}