接下来看Closure组。
Closure
ChainedClosure
IfClosure
WhileClosure
ClosureUtils
Closure这一组接口和类提供一个操作对象的execute方法，为我们在处理一系列对象时可以将处理逻辑分离出来。理论上讲，使用Transformer也可以达到类似的效果，只要输出对象和输入对象是同一个对象就好，但是Closure接口定义的execute方法返回void，并且从效果和功能区分上，Closure可以更好的诠释对象处理或执行的意思。而事实上，ClosureUtils中也提供了一个asClosure方法包装一个现成的Transformer。
沿用前面的Emploee类，我们来给一组员工涨工资：
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());
}
}
}
以下是运行结果：
=========== 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]
========================================
我这里举的是一个相对简单的例子，在Closure这一组还有一些很方便的类，如ChainedClosure可以包装一组Closure作为整体执行；IfClosure在创建时需要提供给它一个Predicate和两个Closure，执行时先做Predicate判定再决定执行哪一个Closure；SwitchClosure跟SwitchTransformer类似，根据创建时传入的Predicate组和Closure组对应执行；WhileClosure则根据创建时传入的Predicate做判断，如果为true则执行Closure，直到Predicate返回false；等等。
具体用法请参考Javadoc。