接下來看Closure組。
Closure
ChainedClosure
IfClosure
WhileClosure
ClosureUtils
Closure這一組接口和類提供一個操作對象的execute方法，為我們在處理一系列對象時可以將處理邏輯分離出來。理論上講，使用Transformer也可以達到類似的效果，只要輸出對象和輸入對象是同一個對象就好，但是Closure接口定義的execute方法返回void，并且從效果和功能區分上，Closure可以更好的詮釋對象處理或執行的意思。而事實上，ClosureUtils中也提供了一個asClosure方法包裝一個現成的Transformer。
沿用前面的Emploee類，我們來給一組員工漲工資：
package sean.study.commons.collections;
import java.util.Arrays;
import java.util.Collection;
import java.util.Date;
import java.util.Iterator;
import org.apache.commons.collections.Closure;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.lang.StringUtils;
public class ClosureUsage {
public static void main(String[] args) {
demoClosureUsage();
}
public static void demoClosureUsage() {
System.out.println(StringUtils.center(" demoClosureUsage ", 40, "="));
// data setup
Employee[] employees = new Employee[] {
new Employee("Tony", 26, new Date(), "E4", 2000),
new Employee("Michelle", 24, new Date(), "E4", 2000),
new Employee("Jack", 28, new Date(), "E5", 3000)
};
Collection empColl = Arrays.asList(employees);
printColl("Before salary increase:", empColl);
// closure setup
Closure salaryIncreaseClosure = new Closure() {
public void execute(Object obj) {
Employee emp = (Employee) obj;
emp.setSalary(emp.getSalary() * 1.20);
}
};
// salary increase
CollectionUtils.forAllDo(empColl, salaryIncreaseClosure);
printColl("After salary increase:", empColl);
System.out.println(StringUtils.repeat("=", 40));
}
public static void printColl(String label, Collection c) {
if (StringUtils.isNotBlank(label)) {
System.out.println(label);
}
Iterator iter = c.iterator();
while (iter.hasNext()) {
System.out.println(iter.next());
}
}
}
以下是運行結果：
=========== demoClosureUsage ===========
Before salary increase:
Employee[name=Tony,age=26,dateJoined=2005-08-05,grade=E4,salary=2000.0]
Employee[name=Michelle,age=24,dateJoined=2005-08-05,grade=E4,salary=2000.0]
Employee[name=Jack,age=28,dateJoined=2005-08-05,grade=E5,salary=3000.0]
After salary increase:
Employee[name=Tony,age=26,dateJoined=2005-08-05,grade=E4,salary=2400.0]
Employee[name=Michelle,age=24,dateJoined=2005-08-05,grade=E4,salary=2400.0]
Employee[name=Jack,age=28,dateJoined=2005-08-05,grade=E5,salary=3600.0]
========================================
我這里舉的是一個相對簡單的例子，在Closure這一組還有一些很方便的類，如ChainedClosure可以包裝一組Closure作為整體執行；IfClosure在創建時需要提供給它一個Predicate和兩個Closure，執行時先做Predicate判定再決定執行哪一個Closure；SwitchClosure跟SwitchTransformer類似，根據創建時傳入的Predicate組和Closure組對應執行；WhileClosure則根據創建時傳入的Predicate做判斷，如果為true則執行Closure，直到Predicate返回false；等等。
具體用法請參考Javadoc。