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20,tomcat的XML解析---digester

 
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tomcat使用server.xml配置属性信息
Tomcat使用开源工具Digester来讲XML元素转换为Java对象
Digester是Apache Jakarta项目下面的开源项目
org.apache.commons.digester.Digester类是Digester库里的主类。使用它来解析XML文档。
对于该文档中的每一个元素,Digester都检查它是否需要做点事情,
只需决定Digester实例在调用parser方法之前需要做什么即可
Digester对象遇到一个XML元素的时候怎么做?很简单,你定义模式并且将模式跟一条或多条规则相关联即可。
XML的根元素有一个跟他的元素名相同的模式
<?xml version="1.0" encoding="ISO-8859-1"?>
 <employee firstName="Brian" lastName="May">
  <office>
  <address streeName="Wellington Street" streetNumber="110"/>
  </office>
 </employee>
该文档的根元素师employee,该元素的模式emploee。它的office元素是<employee>的子元素。
一个子元素的模式是它的名字加上它属于的元素作为前缀。所以office元素的模式是employee/office,
而address元素的模式是:
Address元素的父元素师<office>,<office>元素的模式employee/office。因此,<address>的模式employee/office/address。

规则(rules)
一个规则定义了Digester遇到特别的模式的时候必须做的动作。一个规则用org.apache.commons.digester.Rule类。
Digester类包括零个或多个Rule对象。
在一个Digester实例中,规则及其模式被存储在接口org.apache.commons.digester.Rules定义的类型中
每一次给Digester实例添加规则,都将Rule对象添加到Rules对象。
在Rule中有两个方法:begin方法和end方法。当解析一个XML文档的时候,遇到开始元素,
Digester实例调用Rule对象的begin方法,而遇到结束元素的时候调用stop方法。
example.xml所示的文档的时候,下面是Digester对象所作的.
· 第一次遇到employee开始元素,检查是否已经有存在的规则模式employee。
如果有,Digester调用Rule对象的begin方法,从begin方法开始添加第一个模式。
· 然后检查office元素,所以Digester对象检查是否存在规则模式为employee/office。如果有,,调用Rule对象的begin方法、
· 接下来检查模式employee/office/address,如果找到了规则,则调用begin方法
· 接下来Digester遇到了address结束符,调用对应规则的end方法。
· 解析来遇到了office结束符,调用相应规则的end方法。
· 最后遇到了employee结束符,调用相应规则的end方法。
Digester预先定义了一些规则,甚至在不了解Rule类的时候都可以使用这些规则。但是,如果这些规则不足够,需要建立自己的规则

创建对象
如果想让Digester给特定的规则创建对象,可以调用它的addObjectCreate方法。
该方法有四个实现,其中两个最常用方法的签名如下:
public void addObjectCreate(java.lang.String pattern, java.lang.Class clazz)
public void addObjectCreate(java.lang.String pattern, java.lang.String className)
传递一个模式和类对象(或者是类名)给它们.
例如,你想Digester根据employee模式,创建一个Employee对象(类为ex15.pyrmont.digestertest.Employee)可以使用如下代码:
digester.addObjectCreate("employee", ex15.pyrmont.digestertest.Employee.class);
或者 digester.addObjectCreate("employee", "ex15.pyrmont.digestertest.Employee");
方法addObjectCreate的另外两个实现允许在XML文档中定义类名,而不是通过作为方法参数。
这个特性带来了强大的功能,它使得类名可以在运行时决定,下面是这两个方法的签名:
public void addObjectCreate(java.lang.String pattern, java.lang.String className, java.lang.String attributeName)
public void addObjectCreate(java.lang.String pattern, java.lang.String attributeName, java.lang.Class clazz)
在这两个实现中,attributeName参数定义了XML文档中的属性,名字有className指定。
例如,如果使用下面的代码来定义创建对象规则: digester.addObjectCreate("employee", null, "className");
其中属性名为className 然后在XML中传递类名:
<employee firstName="Brian" lastName="May" className="ex15.pyrmont.digestertest.Employee">
或者可以如下在addObjectCreate方法中定义默认的类名:
digester.addObjectCreate("employee", "ex15.pyrmont.digestertest.Employee", "className");
使用addObejectCreate方法创建的对象被压到一个内部堆栈中,并定义来peek、push以及pop方法来操作创建的对象。

设置属性
另一个重要的方法是addSetProperties,Digester对象可以通过它设置对象属性。
该方法的一个实现的签名如下:
public void addSetProperties(java.lang.String pattern)
传递一个模式给该方法,例如下面的代码:
digester.addObjectCreate("employee","ex15.pyrmont.digestertest.Employee");
digester.addSetProperties("employee");
上面的Digester实例有两个规则:创建对象,设置属性。
都是关于employee模式的。根据添加的顺序来执行这些规则。
XML文档中如下的employee元素 <employee firstName="Brian" lastName="May">

方法调用
Digester允许通过添加规则,见到相应的模式的时候就调用栈最高层中对象的方法。该方法名为addCallMethod,
它的一个实现的签名如下:
public void addCallMethod (java.lang.String pattern, java.lang.String methodName)

建立对象间的联系
Digester实例有一个栈用来临时存储对象。当调用addObjectCreate创建对象后,将对象压入堆栈中。
可以把堆栈想象成一口井,可以将对象放入到井中,而pop方法相当于取出井中最上边的元素。
当通过addObjectCreate方法创建两个对象的时候,第一个对象被放入井中,然后是第二个。
addSetNext用于建立第一个对象和第二个对象之间的关系,
它把第二个对象作为参数传递给第一个对象。
下面是addSetNext方法的签名
public void addSetNext(java.lang.String pattern, java.lang.String methodName)
参数argument定义了触发该规则的模式,methodName参数是是第一个对象要被调用的方法名。
该模式的形式如firstObject/secondObject。
例如,一个employee可以有一个office,要创建一个employee和他的office之间的关系,
首先需要使用两个addObjectCreate方法。
digester.addObjectCreate("employee", "ex15.pyrmont.digestertest.Employee");
digester.addObjectCreate("employee/office", "ex15.pyrmont.digestertest.Office");
第一个addObjectCreate方法根据employee元素创建一个Employee类实例。
第二个addObjectCreate方法根据<employee>下面的<office>创建一个Office实例。
现在对象在栈底部,Office对象在栈顶部。要建立它们之间的关系,可以使用addSetNext方法方法:
digester.addSetNext("employee/office", "addOffice");
其中addOffice是Employee类的方法,该方法必须接受一个Office对象作为参数

验证XML文档
可以使用Digester来对XML文档的结构进行验证,一个XML文档是否合法取决于由Digester定义的validating属性,
该属性的默认值为false。
方法setValidating用来用来设置是否要验证XML文档,该方法的签名如下:
public void setValidating(boolean validating)

 

例子

 

public class Employee {

	private String firstName;
	private String lastName;
	private ArrayList offices = new ArrayList();

	public Employee() {
		System.out.println("Creating Employee");
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		System.out.println("Setting firstName : " + firstName);
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		System.out.println("Setting lastName : " + lastName);
		this.lastName = lastName;
	}

	public void addOffice(Office office) {
		System.out.println("Adding Office to this employee");
		offices.add(office);
	}

	public ArrayList getOffices() {
		return offices;
	}

	public void printName() {
		System.out.println("My name is " + firstName + " " + lastName);
	}
}

 

 

public final class Test01 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String path = System.getProperty("user.dir") + File.separator + "etc";
		File file = new File(path, "employee1.xml");
		Digester digester = new Digester();
		// add rules
		digester.addObjectCreate("employee",
				"ex15.pyrmont.digestertest.Employee");
		digester.addSetProperties("employee");
		digester.addCallMethod("employee", "printName");
		try {
			Employee employee = (Employee) digester.parse(file);
			System.out.println("First name : " + employee.getFirstName());
			System.out.println("Last name : " + employee.getLastName());
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

 

 


<?xml version="1.0" encoding="ISO-8859-1"?>
<employee firstName="Brian" lastName="May">
</employee>

运行Test01类得到如下运行结果:
Creating Employee
Setting firstName : Brian
Setting lastName : May
My name is Brian May
First name : Brian
Last name : May

当调用Digester对象的parse方法的时候,它打开XML文档开始解析它。首先,Digester看到了employee的开始元素。
这样触发了关于employee模式的三个规则,第一个是创建一个对象,
所以Digester初始化一个Employee类的对象,这样需要调用Employee类的构造函数,
该构造函数打印出字符串“Creating Employee”。
第二个规则设置Employee对象的属性,该元素有两个属性:firstName和lastName。
该规则调用方法这两个属性的set方法。这两个set方法打印出如下字符串
Setting firstName : Brian
Setting lastName : May

第三个规则调用printName方法,打印出如下内容:
My name is Brian May

接下来,最后两行诗调用getFirstName和getLastName方法的结果。
First name : Brian
Last name : May


例子2
第二个例子说明了如何创建两个对象,并建立它们之间的关系。

 

public class Office {

	private Address address;
	private String description;

	public Office() {
		System.out.println("..Creating Office");
	}

	public String getDescription() {
		return description;
	}

	public void setDescription(String description) {
		System.out.println("..Setting office description : " + description);
		this.description = description;
	}

	public Address getAddress() {
		return address;
	}

	public void setAddress(Address address) {
		System.out.println("..Setting office address : " + address);
		this.address = address;
	}
}

 

调用父对象的方法来建立它们之间的关系

public class Address {

	private String streetName;
	private String streetNumber;

	public Address() {
		System.out.println("....Creating Address");
	}

	public String getStreetName() {
		return streetName;
	}

	public void setStreetName(String streetName) {
		System.out.println("....Setting streetName : " + streetName);
		this.streetName = streetName;
	}

	public String getStreetNumber() {
		return streetNumber;
	}

	public void setStreetNumber(String streetNumber) {
		System.out.println("....Setting streetNumber : " + streetNumber);
		this.streetNumber = streetNumber;
	}

	public String toString() {
		return "...." + streetNumber + " " + streetName;
	}
}

 

第二个Digester例子说明如何创建多个对象并建立它们之间的关系

 

import java.io.File;
import java.util.ArrayList;
import java.util.Iterator;

import com.sun.org.apache.commons.digester.Digester;

public class Test02 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		String path = System.getProperty("user.dir") + File.separator + "etc";
		File file = new File(path, "employee2.xml");
		Digester digester = new Digester();
		// add rules
		digester.addObjectCreate("employee",
				"ex15.pyrmont.digestertest.Employee");
		digester.addSetProperties("employee");
		digester.addObjectCreate("employee/office",
				"ex15.pyrmont.digestertest.Office");
		digester.addSetProperties("employee/office");
		digester.addSetNext("employee/office", "addOffice");
		digester.addObjectCreate("employee/office/address",
				"ex15.pyrmont.digestertest.Address");
		digester.addSetProperties("employee/office/address");
		digester.addSetNext("employee/office/address", "setAddress");
		try {
			Employee employee = (Employee) digester.parse(file);
			ArrayList offices = employee.getOffices();
			Iterator iterator = offices.iterator();
			System.out
					.println("-------------------------------------------------");
			while (iterator.hasNext()) {
				Office office = (Office) iterator.next();
				Address address = office.getAddress();
				System.out.println(office.getDescription());
				System.out.println("Address : " + address.getStreetNumber()
						+ " " + address.getStreetName());
				System.out.println(" -------------------------------");
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

 

 

xml如下
<?xml version="1.0" encoding="ISO-8859-1"?>
<employee firstName="Freddie" lastName="Mercury">
 <office description="Headquarters">
  <address streetName="Wellington Avenue" streetNumber="223"/>
 </office>
 <office description="Client site">
  <address streetName="Downing Street" streetNumber="10"/>
 </office>
</employee>

Rule类

Rule 类有多个方法,其中两个最重要的是begin和end方法。
当Digester实例遇到一个XML元素的开始标志的使用,调用所有匹配规则的begin方法。Rule类的begin方法签名如下
public void begin(org.xml.sax.Attributes attributes) throws java.lang.Exception
当Digester实例遇到XML元素的end时候,调用所有匹配规则的end方法
public void end() throws java.lang.Exception

每次调用addObjectCreate、addCallMethod、addSetNext方法的或者该类其它的方法的时候,
都会间接的调用Digester类的addRule方法,该方法会将一个Rule对象以及它的匹配模式添加到Didgester内部的规则集合中。
addRule 方法的签名如下
public void addRule(java.lang.String pattern, Rule rule)
该方法在Digester类中的实现如下:
public void addRule(String pattern, Rule rule) {
 rule.setDigester(this);
 getRules().add(pattern, rule);
}

addObjectCreate方法的实现:
public void addObjectCreate(String pattern, String className) {
 addRule(pattern, new ObjectCreateRule(className));
}
public void addObjectCreate(String pattern, Class clazz) {
 addRule(pattern, new ObjectCreateRule(clazz));
}
都调用了addRule方法,ObjectCreateRule类是Rule类的子类
begin和end方法在ObjectCreateRule类中的实现

public void begin(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); 
	}
	// Instantiate the new object and push it on the context stack 
	Class clazz = digester.getClassLoader().loadclass(realClassName);
	Object instance = clazz.newInstance(); 
	digester.push(instance); 
}

public void end() throws Exception {
	Object top = digester.pop(); 
}

 

在begin方法中的最后三行创建了对象并将其压到Digester类的内部堆栈中,end方法使用pop方法从堆栈中获得对象。


RuleSet的使用
另一种往Digester实例添加规则方法是调用addRuleSet方法,该方法的签名如下:
public void addRuleSet(RuleSet ruleSet)
RuleSet表示了Rule对象,该接口定义了两个方法:addRuleInstance和getNamespaceURI
public void addRuleInstance(Digester digester)
方法addRuleInstance将在当前RuleSet中定义的Rule对象添加到Digester实例中,参数就是该对象。
方法getNamespaceURI返回用于请求所有规则对象的名字空间URI,它的签名如下:
public java.lang.String getNamespaceURI()
在创建完一个Digester对象后,可以创建RuleSet对象并传递一个RuleSet对象给addRuleSet方法。
有一个基本类RuleSetBase实现了RuleSet接口,RuleSetBase是一个抽象类,
它提供了getNamespaceURI的实现,你需要做的只是提供addRuleInstances的实现即可。

 

public class EmployeeRuleSet extends RuleSetBase {

	@Override
	public void addRuleInstances(Digester digester) {
		digester.addObjectCreate("employee",
				"ex15.pyrmont.digestertest.Employee");
		digester.addSetProperties("employee");
		digester.addObjectCreate("employee/office",
				"ex15.pyrmont.digestertest.Office");
		digester.addSetProperties("employee/office");
		digester.addSetNext("employee/office", "addOffice");
		digester.addObjectCreate("employee/office/address",
				"ex15.pyrmont.digestertest.Address");
		digester.addSetProperties("employee/office/address");
		digester.addSetNext("employee/office/address", "setAddress");
	}

}

 

注意addRuleInstances方法在EmployeeRuleSet中的实现跟Test02添加了相同的规则

 

public class Test03 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String path = System.getProperty("user.dir") + File.separator + "etc";
		File file = new File(path, "employee2.xml");
		Digester digester = new Digester();
		digester.addRuleSet(new EmployeeRuleSet());
		try {
			Employee employee = (Employee) digester.parse(file);
			ArrayList offices = employee.getOffices();
			Iterator iterator = offices.iterator();
			System.out.println("-------------------------------------------------");
			while (iterator.hasNext()) {
				Office office = (Office) iterator.next();
				Address address = office.getAddress();
				System.out.println(office.getDescription());
				System.out.println("Address : " + address.getStreetNumber()
						+ " " + address.getStreetName());
				System.out.println("-------------------------------");
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

 

 

注意Test03比较短,因为它将添加规则对象的操作隐藏到了EmployeeRuleSet类中。

ContextConfig类
跟其它类型的容器不同,StandardContext必须有一个监听器,
该监听器用于配置StandardContext对象并将StandardContext的configured变量设置为true。
,StandardContext的标准监听器是org.apache.catalina.startup.ContextConfig类的实例。
不像简单的SimpleContextConfig类,ContextConfig做了很多有用的工作
例如,ContextConfig实例给StandardContext的流水线安装一个验证阀门。它还给流水线添加一个证书阀门。
更重要的是,ContextConfig实例还读并解析默认的web.xml文件,并将其中的XML元素转换为Java对象
ContextConfig为每一个Servlet元素创建了一个StandardWrapper实例

defaultConfig 方法
方法defaultConfig读取并解析默认的%CATALINA_HOME%/conf目录下面的web.xml。

 

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方法首先传教一个File对象指向默认的web.xml。
DefaultWebXML的值可以在org.apache.catalina.startup.Constants中找到:
public static final String DefaultWebXml = "conf/web.xml";
然后方法defaultConfig处理web.xml文件。它对webDigester对象枷锁,然后解析该文件。
webDigester变量指向一个Digester对象的实例,该实例用于处理web.xml并添加规则。


applicationConfig 方法
applicationConfig方法与defaultConfig方法相似,除了处理应用程序部署文件的地方。
一个应用的部署文件在该应用目录下的WEB-INF目录下面

   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);
                }
            }
        }

    }

 

 

创建web Digester
在ContextConfig类中存在一个名为webDigester的Digester对象:
private static Digester webDigester = createWebDigester();
该Digester用于解析默认web.xml以及应用程序web.xml。
处理web.xml的规则在调用createWebDigester方法的时候会被添加

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());
        webDigester.addRuleSet(new WebRuleSet());
        return (webDigester);

    }

 

 

注意createWebDigester方法在webDigester中调用addRuleSet的时候传递一个WebRuleSet实例.
WebRuleSet是RuleSetBase类的一个子类

 

public class WebRuleSet extends RuleSetBase {


    // ----------------------------------------------------- Instance Variables


    /**
     * The matching pattern prefix to use for recognizing our elements.
     */
    protected String prefix = null;


    // ------------------------------------------------------------ Constructor


    /**
     * Construct an instance of this <code>RuleSet</code> with the default
     * matching pattern prefix.
     */
    public WebRuleSet() {

        this("");

    }


    /**
     * Construct an instance of this <code>RuleSet</code> with the specified
     * matching pattern prefix.
     *
     * @param prefix Prefix for matching pattern rules (including the
     *  trailing slash character)
     */
    public WebRuleSet(String prefix) {

        super();
        this.namespaceURI = null;
        this.prefix = prefix;

    }


    // --------------------------------------------------------- Public Methods


    /**
     * <p>Add the set of Rule instances defined in this RuleSet to the
     * specified <code>Digester</code> instance, associating them with
     * our namespace URI (if any).  This method should only be called
     * by a Digester instance.</p>
     *
     * @param digester Digester instance to which the new Rule instances
     *  should be added.
     */
    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/ejb-local-ref",
                                 "org.apache.catalina.deploy.ContextLocalEjb");
        digester.addSetNext(prefix + "web-app/ejb-local-ref",
                            "addLocalEjb",
                            "org.apache.catalina.deploy.ContextLocalEjb");

        digester.addCallMethod(prefix + "web-app/ejb-local-ref/description",
                               "setDescription", 0);
        digester.addCallMethod(prefix + "web-app/ejb-local-ref/ejb-link",
                               "setLink", 0);
        digester.addCallMethod(prefix + "web-app/ejb-local-ref/ejb-ref-name",
                               "setName", 0);
        digester.addCallMethod(prefix + "web-app/ejb-local-ref/ejb-ref-type",
                               "setType", 0);
        digester.addCallMethod(prefix + "web-app/ejb-local-ref/local",
                               "setLocal", 0);
        digester.addCallMethod(prefix + "web-app/ejb-local-ref/local-home",
                               "setHome", 0);

        digester.addObjectCreate(prefix + "web-app/ejb-ref",
                                 "org.apache.catalina.deploy.ContextEjb");
        digester.addSetNext(prefix + "web-app/ejb-ref",
                            "addEjb",
                            "org.apache.catalina.deploy.ContextEjb");

        digester.addCallMethod(prefix + "web-app/ejb-ref/description",
                               "setDescription", 0);
        digester.addCallMethod(prefix + "web-app/ejb-ref/ejb-link",
                               "setLink", 0);
        digester.addCallMethod(prefix + "web-app/ejb-ref/ejb-ref-name",
                               "setName", 0);
        digester.addCallMethod(prefix + "web-app/ejb-ref/ejb-ref-type",
                               "setType", 0);
        digester.addCallMethod(prefix + "web-app/ejb-ref/home",
                               "setHome", 0);
        digester.addCallMethod(prefix + "web-app/ejb-ref/remote",
                               "setRemote", 0);

        digester.addObjectCreate(prefix + "web-app/env-entry",
                                 "org.apache.catalina.deploy.ContextEnvironment");
        digester.addSetNext(prefix + "web-app/env-entry",
                            "addEnvironment",
                            "org.apache.catalina.deploy.ContextEnvironment");

        digester.addCallMethod(prefix + "web-app/env-entry/description",
                               "setDescription", 0);
        digester.addCallMethod(prefix + "web-app/env-entry/env-entry-name",
                               "setName", 0);
        digester.addCallMethod(prefix + "web-app/env-entry/env-entry-type",
                               "setType", 0);
        digester.addCallMethod(prefix + "web-app/env-entry/env-entry-value",
                               "setValue", 0);

        digester.addObjectCreate(prefix + "web-app/error-page",
                                 "org.apache.catalina.deploy.ErrorPage");
        digester.addSetNext(prefix + "web-app/error-page",
                            "addErrorPage",
                            "org.apache.catalina.deploy.ErrorPage");

        digester.addCallMethod(prefix + "web-app/error-page/error-code",
                               "setErrorCode", 0);
        digester.addCallMethod(prefix + "web-app/error-page/exception-type",
                               "setExceptionType", 0);
        digester.addCallMethod(prefix + "web-app/error-page/location",
                               "setLocation", 0);

        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.addObjectCreate(prefix + "web-app/login-config",
                                 "org.apache.catalina.deploy.LoginConfig");
        digester.addSetNext(prefix + "web-app/login-config",
                            "setLoginConfig",
                            "org.apache.catalina.deploy.LoginConfig");

        digester.addCallMethod(prefix + "web-app/login-config/auth-method",
                               "setAuthMethod", 0);
        digester.addCallMethod(prefix + "web-app/login-config/realm-name",
                               "setRealmName", 0);
        digester.addCallMethod(prefix + "web-app/login-config/form-login-config/form-error-page",
                               "setErrorPage", 0);
        digester.addCallMethod(prefix + "web-app/login-config/form-login-config/form-login-page",
                               "setLoginPage", 0);

        digester.addCallMethod(prefix + "web-app/mime-mapping",
                               "addMimeMapping", 2);
        digester.addCallParam(prefix + "web-app/mime-mapping/extension", 0);
        digester.addCallParam(prefix + "web-app/mime-mapping/mime-type", 1);

        digester.addCallMethod(prefix + "web-app/resource-env-ref",
                               "addResourceEnvRef", 2);
        digester.addCallParam(prefix + "web-app/resource-env-ref/resource-env-ref-name", 0);
        digester.addCallParam(prefix + "web-app/resource-env-ref/resource-env-ref-type", 1);

        digester.addObjectCreate(prefix + "web-app/resource-ref",
                                 "org.apache.catalina.deploy.ContextResource");
        digester.addSetNext(prefix + "web-app/resource-ref",
                            "addResource",
                            "org.apache.catalina.deploy.ContextResource");

        digester.addCallMethod(prefix + "web-app/resource-ref/description",
                               "setDescription", 0);
        digester.addCallMethod(prefix + "web-app/resource-ref/res-auth",
                               "setAuth", 0);
        digester.addCallMethod(prefix + "web-app/resource-ref/res-ref-name",
                               "setName", 0);
        digester.addCallMethod(prefix + "web-app/resource-ref/res-sharing-scope",
                               "setScope", 0);
        digester.addCallMethod(prefix + "web-app/resource-ref/res-type",
                               "setType", 0);

        digester.addObjectCreate(prefix + "web-app/security-constraint",
                                 "org.apache.catalina.deploy.SecurityConstraint");
        digester.addSetNext(prefix + "web-app/security-constraint",
                            "addConstraint",
                            "org.apache.catalina.deploy.SecurityConstraint");

        digester.addRule(prefix + "web-app/security-constraint/auth-constraint",
                         new SetAuthConstraintRule(digester));
        digester.addCallMethod(prefix + "web-app/security-constraint/auth-constraint/role-name",
                               "addAuthRole", 0);
        digester.addCallMethod(prefix + "web-app/security-constraint/display-name",
                               "setDisplayName", 0);
        digester.addCallMethod(prefix + "web-app/security-constraint/user-data-constraint/transport-guarantee",
                               "setUserConstraint", 0);

        digester.addObjectCreate(prefix + "web-app/security-constraint/web-resource-collection",
                                 "org.apache.catalina.deploy.SecurityCollection");
        digester.addSetNext(prefix + "web-app/security-constraint/web-resource-collection",
                            "addCollection",
                            "org.apache.catalina.deploy.SecurityCollection");
        digester.addCallMethod(prefix + "web-app/security-constraint/web-resource-collection/http-method",
                               "addMethod", 0);
        digester.addCallMethod(prefix + "web-app/security-constraint/web-resource-collection/url-pattern",
                               "addPattern", 0);
        digester.addCallMethod(prefix + "web-app/security-constraint/web-resource-collection/web-resource-name",
                               "setName", 0);

        digester.addCallMethod(prefix + "web-app/security-role/role-name",
                               "addSecurityRole", 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",
                              "setServletClass", 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


/**
 * A Rule that calls the <code>setAuthConstraint(true)</code> method of
 * the top item on the stack, which must be of type
 * <code>org.apache.catalina.deploy.SecurityConstraint</code>.
 */

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)");
    }

}


/**
 * Class that calls <code>setDistributable(true)</code> for the top object
 * on the stack, which must be a <code>org.apache.catalina.Context</code>.
 */

final class SetDistributableRule extends Rule {

    public SetDistributableRule(Digester digester) {
        super(digester);
    }

    public void begin(Attributes attributes) throws Exception {
        Context context = (Context) digester.peek();
        context.setDistributable(true);
        if (digester.getDebug() > 0)
            digester.log(context.getClass().getName() +
                         ".setDistributable( true)");
    }

}


/**
 * Class that calls a property setter for the top object on the stack,
 * passing the public ID of the entity we are currently processing.
 */

final class SetPublicIdRule extends Rule {

    public SetPublicIdRule(Digester digester, String method) {
        super(digester);
        this.method = method;
    }

    private String method = null;

    public void begin(Attributes attributes) throws Exception {

        Context context = (Context) digester.peek(digester.getCount() - 1);
        Object top = digester.peek();
        Class paramClasses[] = new Class[1];
        paramClasses[0] = "String".getClass();
        String paramValues[] = new String[1];
        paramValues[0] = digester.getPublicId();

        Method m = null;
        try {
            m = top.getClass().getMethod(method, paramClasses);
        } catch (NoSuchMethodException e) {
            digester.log("Can't find method " + method + " in " + top +
                         " CLASS " + top.getClass());
            return;
        }

        m.invoke(top, paramValues);
        if (digester.getDebug() >= 1)
            digester.log("" + top.getClass().getName() + "." + method +
                        "(" + paramValues[0] + ")");

    }

}


/**
 * A Rule that calls the factory method on the specified Context to
 * create the object that is to be added to the stack.
 */

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());
    }

}

 


Tomcat使用的是不同的配置,简单的配置配置使用server.xml文件通过Digester对象将XML元素转换为Java对象。
另外,一个web.xml文档被用于配置servlet/JSP应用。Tomcat必须能够解析web.xml文档并基于XML文档配置上下问对象,
Digester优雅的解决了这个问题。

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