上一篇對Digester做了基本介紹，也已經了解了Digester的基本使用方法，接下來將繼續學習其相關特性，本篇主要涉及以下幾個內容：
規則模組綁定，透過定義一個RulesModule介面實作類別來完成規則的預先綁定，運行時重複使用
非同步解析xml
解析xml中的變量，如${sys.user}
#使用帶參數的建構方法建立對象，參數來自xml節點數據
在此之前，我們使用Digester的基本流程都是每次在程式執行時綁定規則，然後解析;
事實上，我們可以改變Digester的解析流程，啟動的時候預先定義規則集，然後在運行的時候重複使用預先定義的規則；
可能這樣說比較空泛，可以看一下如下一個Web應用場景，應該就會有一個比較深刻的理解了；
熟悉Web開發的應該都知道servlet了，這裡就不細說了，假設有一個EmployeeServlet，如下所示：
由於servlet是單例的，而且Digester不是線程安全的，所以我們會在每次請求的時候，new出一個Digester對象，來保證線程安全，寫法如下：
public class EmployeeServlet extends HttpServlet
{public void doGet(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException
{
Digester digester = new Digester();
digester.setNamespaceAware( true );
digester.setXIncludeAware( true );
digester.addObjectCreate( "employee", Employee.class );
digester.addCallMethod( "employee/firstName", "setFirstName", 0 );
digester.addCallMethod( "employee/lastName", "setLastName", 0 );
digester.addObjectCreate( "employee/address", Address.class );
digester.addCallMethod( "employee/address/type", "setType", 0 );
digester.addCallMethod( "employee/address/city", "setCity", 0 );
digester.addCallMethod( "employee/address/state", "setState", 0 );
digester.addSetNext( "employee/address", "addAddress" );
Employee employee = digester.parse( openStream( req.getParameter( "employeeId" ) ) );
...
}我們可以很容易發現以上程序的缺點：代碼沒有復用，每次請求都需要重複綁定規則；
不過，我們可以使用RuleSet來解決程式碼沒有重複使用的問題，如下所示，定義一個EmployeeRuleSet規則集實作RuleSet 介面：
public class EmployeeRuleSet implements RuleSet
{public void addRuleInstances( Digester digester )
{
digester.addObjectCreate( "employee", Employee.class );
digester.addCallMethod( "employee/firstName", "setFirstName", 0 );
digester.addCallMethod( "employee/lastName", "setLastName", 0 );
digester.addObjectCreate( "employee/address", Address.class );
digester.addCallMethod( "employee/address/type", "setType", 0 );
digester.addCallMethod( "employee/address/city", "setCity", 0 );
digester.addCallMethod( "employee/address/state", "setState", 0 );
digester.addSetNext( "employee/address", "addAddress" );
}
}然後在servlet中這樣使用：
public class EmployeeServlet extends HttpServlet
{private final RuleSet employeeRuleSet = new EmployeeRuleSet();public void doGet(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException
{
Digester digester = new Digester();
digester.setNamespaceAware( true );
digester.setXIncludeAware( true );
employeeRuleSet.addRuleInstances( digester );
Employee employee = digester.parse( openStream( req.getParameter( "employeeId" ) ) );
...
}
}很顯然這樣做是沒有錯誤的（其實，個人覺得不如直接寫一個私有方法，加入規則，哈哈），但有以下缺點：
RuleSet其實並不是配置，只是給digester綁定下規則而已;
digester物件與客戶端耦合度比較高，直接由客戶端建立；
每次解析呼叫前，都需要重複綁定規則
#規則綁定的時候，語意性很差，可讀性不好；
那麼，最佳實踐是什麼呢，答案是使用RulesModule接口，幫助我們啟動時預先綁定規則，然後運行的時候，重複使用預先綁定的規則即可，如下所示：
定義一個RulesModule介面實作類別：
class EmployeeModuleextends AbstractRulesModule
{
@Overrideprotected void configure()
{
forPattern( "employee" ).createObject().ofType( Employee.class );
forPattern( "employee/firstName" ).setBeanProperty();
forPattern( "employee/lastName" ).setBeanProperty();
forPattern( "employee/address" ).createObject().ofType( Address.class ).then().setNext( "addAddress");
forPattern( "employee/address/type" ).setBeanProperty();
forPattern( "employee/address/city" ).setBeanProperty();
forPattern( "employee/address/state" ).setBeanProperty();
}
}然後在servlet這樣使用：
public class EmployeeServletextends HttpServlet
{private final DigesterLoader loader = newLoader( new EmployeeModule() )
.setNamespaceAware( true )
.setXIncludeAware( true );public void doGet(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException
{
Digester digester = loader.newDigester()
Employee employee = digester.parse( openStream( req.getParameter("employeeId") ) );
...
}
}好處顯而易見：
RulesModule規則綁定的API語意化很強，使用簡便，可讀性高；
規則綁定的配置移到了啟動階段來完成；
#digester物件不是由客戶端來創建，而是透過DigesterLoader創建；
#除了自己寫類別實作RulesModule介面外，digester本身提供了一個FromXmlRulesModule類別 #，就已經實作了RulesModule接口，我們可以這樣使用：
##DigesterLoader loader = DigesterLoader.newLoader( .getResource( "myrule.xml"
<employee> <firstName>Pi</firstName> <lastName>Chen</lastName> <address> <type>CITY</type> <city>HangZhou</city> <state>2</state> </address> </employee>
##
package apache.commons.digester3.example.rulesbinder.module;import org.apache.commons.digester3.binder.AbstractRulesModule;import apache.commons.digester3.example.rulesbinder.pojo.Address;import apache.commons.digester3.example.rulesbinder.pojo.Employee;/**
*
*
* @author
* @version 2017年6月5日 */public class EmployeeModule extends AbstractRulesModule {
@Overrideprotected void configure() {
forPattern("employee").createObject().ofType(Employee.class);
forPattern("employee/firstName").setBeanProperty();
forPattern("employee/lastName").setBeanProperty();
forPattern("employee/address").createObject().ofType(Address.class).then().setNext("addAddress");
forPattern("employee/address/type").setBeanProperty();
forPattern("employee/address/city").setBeanProperty();
forPattern("employee/address/state").setBeanProperty();
}
}package apache.commons.digester3.example.rulesbinder;import java.io.IOException;import org.apache.commons.digester3.Digester;import org.apache.commons.digester3.binder.DigesterLoader;import org.xml.sax.SAXException;import apache.commons.digester3.example.rulesbinder.module.EmployeeModule;import apache.commons.digester3.example.rulesbinder.pojo.Address;import apache.commons.digester3.example.rulesbinder.pojo.Employee;import apache.commons.digester3.example.simpletest.ExampleMain;/**
*
*
* @author
* @version 2017年6月5日 */public class DigesterLoaderMain {private static DigesterLoader dl = DigesterLoader.newLoader(new EmployeeModule())
.setNamespaceAware(false);public static void main(String[] args) {try {
Digester digester = dl.newDigester();
Employee employee = digester.parse(ExampleMain.class.getClassLoader().getResourceAsStream("employee.xml"));
System.out.print(employee.getFirstName() + " ");
System.out.print(employee.getLastName() + ", ");for (Address a : employee.getAddressList()) {
System.out.print(a.getType() + ", ");
System.out.print(a.getCity() + ", ");
System.out.println(a.getState());
}
} catch (IOException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
}
}
}Pi Chen, CITY, HangZhou, 2
digester物件並不是線程安全的，如下是一個簡單的API使用範例：承接上一個例子，使用同樣的xml和RulesModule實作類別;
#客戶端類別：
package apache.commons.digester3.example.rulesbinder;import java.util.concurrent.ExecutionException;import java.util.concurrent.Executors;import java.util.concurrent.Future;import org.apache.commons.digester3.Digester;import org.apache.commons.digester3.binder.DigesterLoader;import apache.commons.digester3.example.rulesbinder.module.EmployeeModule;import apache.commons.digester3.example.rulesbinder.pojo.Address;import apache.commons.digester3.example.rulesbinder.pojo.Employee;import apache.commons.digester3.example.simpletest.ExampleMain;/**
*
* @author
* @version 2017年6月5日 */public class AsyncParseMain {private static DigesterLoader dl = DigesterLoader.newLoader(new EmployeeModule())
.setNamespaceAware(false).setExecutorService(Executors.newSingleThreadExecutor());public static void main(String[] args) {try {
Digester digester = dl.newDigester();
Future<Employee> future = digester.asyncParse(ExampleMain.class.getClassLoader().getResourceAsStream("employee.xml"));
Employee employee = future.get();
System.out.print(employee.getFirstName() + " ");
System.out.print(employee.getLastName() + ", ");for (Address a : employee.getAddressList()) {
System.out.print(a.getType() + ", ");
System.out.print(a.getCity() + ", ");
System.out.println(a.getState());
}
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}假設有一個xml如下所示，（其中${type}為變數）：
<employee>
<firstName>Pi</firstName>
<lastName>Chen</lastName>
<address>
<type>${type}</type>
<city>HangZhou</city>
<state>2</state>
</address>
</employee>那么可以这样解析如上xml：
package apache.commons.digester3.example.rulesbinder;import java.io.IOException;import java.util.HashMap;import java.util.Map;import org.apache.commons.digester3.Digester;import org.apache.commons.digester3.Substitutor;import org.apache.commons.digester3.binder.DigesterLoader;import org.apache.commons.digester3.substitution.MultiVariableExpander;import org.apache.commons.digester3.substitution.VariableSubstitutor;import org.xml.sax.SAXException;import apache.commons.digester3.example.rulesbinder.module.EmployeeModule;import apache.commons.digester3.example.rulesbinder.pojo.Address;import apache.commons.digester3.example.rulesbinder.pojo.Employee;import apache.commons.digester3.example.simpletest.ExampleMain;/**
*
*
* @author
* @version 2017年6月5日 */public class SubstitutionMain
{private static DigesterLoader dl = DigesterLoader.newLoader(new EmployeeModule())
.setNamespaceAware(false);public static void main(String[] args)
{try{// set up the variables the input xml can referenceMap<String, Object> vars = new HashMap<String, Object>();
vars.put("user.name", "me");
vars.put("type", "boss");// map ${varname} to the entries in the var mapMultiVariableExpander expander = new MultiVariableExpander();
expander.addSource("$", vars);// allow expansion in both xml attributes and element textSubstitutor substitutor = new VariableSubstitutor(expander);
Digester digester = dl.newDigester();
digester.setSubstitutor(substitutor);
Employee employee = digester
.parse(ExampleMain.class.getClassLoader().getResourceAsStream("employee$.xml"));
System.out.print(employee.getFirstName() + " ");
System.out.print(employee.getLastName() + ", ");for (Address a : employee.getAddressList())
{
System.out.print(a.getType() + ", ");
System.out.print(a.getCity() + ", ");
System.out.println(a.getState());
}
}catch (IOException e)
{
e.printStackTrace();
}catch (SAXException e)
{
e.printStackTrace();
}
}
}简单地说，就是在使用ObjectCreateRule规则的时候，能够传递xml中的值（属性值、body值）给构造方法使用；
如下是一个待解析的xml：
<root> <bean super="false"><rate>9.99</rate> </bean></root>
那么可以这样解析：
package apache.commons.digester3.example.rulesbinder;import java.io.IOException;import org.apache.commons.digester3.Digester;import org.apache.commons.digester3.ObjectCreateRule;import org.apache.commons.digester3.binder.DigesterLoader;import org.xml.sax.SAXException;import apache.commons.digester3.example.rulesbinder.module.EmployeeModule;import apache.commons.digester3.example.rulesbinder.pojo.Address;import apache.commons.digester3.example.rulesbinder.pojo.Employee;import apache.commons.digester3.example.rulesbinder.pojo.MyBean;import apache.commons.digester3.example.simpletest.ExampleMain;/**
*
*
* @author
* @version 2017年6月5日 */public class ConstructorParamsMain
{public static void main(String[] args)
{try{
ObjectCreateRule createRule = new ObjectCreateRule(MyBean.class);
createRule.setConstructorArgumentTypes(Double.class, Boolean.class);
Digester digester = new Digester();
digester.addRule("root/bean", createRule);
digester.addCallParam("root/bean", 1, "super");
digester.addCallParam("root/bean/rate", 0);
MyBean myBean = digester.parse(ConstructorParamsMain.class.getClassLoader()
.getResourceAsStream("constructor-params.xml"));
System.out.println(myBean.getRate());
System.out.println(myBean.isSuper_());
}catch (IOException e)
{
e.printStackTrace();
}catch (SAXException e)
{
e.printStackTrace();
}
}
}结果打印：
以上是Apache 共享消化器的詳細內容。更多資訊請關注PHP中文網其他相關文章！
