Apache Commons Digester 二（規則模塊綁定-RulesModule、異步解析-asyncParse、xml變量Substitutor、帶參構造方法）
阿新 • • 發佈：2017-06-06
對象 property 解決 space getclass bool trace throw object 9.99
前言
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：
- 規則模塊綁定，通過定義一個RulesModule接口實現類來完成規則的預先綁定，運行時重復使用
- 異步解析xml
- 解析xml中的變量，如${sys.user}
- 使用帶參數的構造方法創建對象，參數來自xml節點數據
規則模塊預先綁定 - RulesModule接口
在此之前，我們使用Digester的基本流程都是每次在程序運行時綁定規則，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復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；
servlet場景例子
熟悉Web開發的應該都知道servlet了，這裏就不細說了，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，每次請求都需重復綁定規則；
不過，我們可以使用RuleSet來解決代碼沒有復用的問題，如下所示，定義一個EmployeeRuleSet規則集實現RuleSet接口：
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，個人覺得還不如直接寫一個私有方法，添加規則，哈哈），但是有如下缺點：
- RuleSet實際上並不是配置，只是給digester綁定下規則而已；
- digester對象與客戶端耦合度比較高，直接由客戶端創建；
- 每次解析調用前，都需要重復綁定規則
- 規則綁定的時候，語義性很差，可讀性不好；
那麽，最佳實踐是什麽呢，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，重復使用預先綁定的規則即可，如下所示：
定義一個RulesModule接口實現類：
class EmployeeModule extends AbstractRulesModule { @Override protected 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 EmployeeServlet extends 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語義化很強，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對象不是由客戶端來創建，而是通過DigesterLoader創建；
FromXmlRulesModule
除了自己編寫類實現RulesModule接口外，digester自身提供了一個FromXmlRulesModule類，就已經實現了RulesModule接口，我們可以這樣使用：
DigesterLoader loader = DigesterLoader.newLoader( new FromXmlRulesModule() { @Override protected void loadRules() { loadXMLRules( DigesterLoaderMain.class.getResource( "myrule.xml" ) ); } } );
...
Digester digester = loader.newDigester(); // myrule.xml already parsed
...
Digester newDigester = loader.newDigester(); // myrule.xml won‘t be parsed again!
完整例子
假設有一個xml如下，待解析
<employee>
<firstName>Pi</firstName>
<lastName>Chen</lastName>
<address>
<type>CITY</type>
<city>HangZhou</city>
<state>2</state>
</address>
</employee>
開始編碼，首先，定義一個RulesModule接口實現類：
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 http://www.cnblogs.com/chenpi/ * @version 2017年6月5日 */ public class EmployeeModule extends AbstractRulesModule { @Override protected 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(); } }
編寫客戶端類：
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 http://www.cnblogs.com/chenpi/ * @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(); } } }
結果打印：
Pi Chen, CITY, HangZhou, 2
異步解析XML
異步解析的話，直接調用asyncParse方法即可，不過需要特別註意，因為digester對象並不是線程安全的，如下是一個簡單的API使用示例：
承接上一個例子，使用同樣的xml和RulesModule實現類;
客戶端類：
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 http://www.cnblogs.com/chenpi/ * @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(); } } }
xml變量解析-Substitutor抽象類
這個比較簡單，定義一個VariableSubstitutor實現類，用戶轉換屬性和body中定義的變量值；
假設有一個xml如下所示，（其中${type}為變量）：
<employee>
<firstName>Pi</firstName>
<lastName>Chen</lastName>
<address>
<type>${type}</type>
<city>HangZhou</city>
<state>2</state>
</address>
</employee>
那麽可以這樣解析如上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 http://www.cnblogs.com/chenpi/ * @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 reference Map<String, Object> vars = new HashMap<String, Object>(); vars.put("user.name", "me"); vars.put("type", "boss"); // map ${varname} to the entries in the var map MultiVariableExpander expander = new MultiVariableExpander(); expander.addSource("$", vars); // allow expansion in both xml attributes and element text Substitutor 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(); } } }
帶參構造方法使用示例
簡單地說，就是在使用ObjectCreateRule規則的時候，能夠傳遞xml中的值（屬性值、body值）給構造方法使用；
如下是一個待解析的xml：
<root> <bean super="false"> <rate>9.99</rate> </bean> </root>
那麽可以這樣解析：
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 http://www.cnblogs.com/chenpi/ * @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(); } } }
結果打印：
9.99
false
參考資料
http://commons.apache.org/proper/commons-digester/
代碼參考
https://github.com/peterchenhdu/apache-commons-digester-example
Apache Commons Digester 二（規則模塊綁定-RulesModule、異步解析-asyncParse、xml變量Substitutor、帶參構造方法）