接下来看Transformer组。
Transformer
ChainedTransformer
SwitchTransformer
TransformerUtils
我们有时候需要将某个对象转换成另一个对象供另一组方法调用，而这两类对象的类型有可能并不是出于同一个继承体系的，或者说出了很基本的Object之外没有共同的父类，或者我们根本不关心他们是不是有其他继承关系，甚至就是同一个类的实例只是对我们而言无所谓，我们为了它能够被后续的调用者有意义的识别和处理，在这样的情形，我们就可以利用Transformer。除了基本的转型Transformer之外，Commons Collections还提供了Transformer链和带条件的Transformer，使得我们很方便的组装出有意义的转型逻辑。
假定我们在处理员工聘用时，需要将原来的Applicant对象转换为Employee对象，而Applicant类和Employee类无论继承关系、字段内容、具体业务职能等等都不是同一派系的，只是某些字段是相关的，且要求必要的转换，那么这个时候我们使用Transformer就可以比较方便的实现这项功能，并且由于它的实现是灵活的、模块化的，使得今后的维护也变得清晰和易于处理。代码如下：
/** Applicant.java */
package sean.study.commons.collections;
import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;
public class Applicant {
private String name;
private int age;
private String applyFor;
public Applicant() {
}
public Applicant(String name, int age, String applyFor) {
this.name = name;
this.age = age;
this.applyFor = applyFor;
}
public String toString() {
return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE)
.append("name", name)
.append("age", age)
.append("applyFor", applyFor)
.toString();
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getApplyFor() {
return applyFor;
}
public void setApplyFor(String applyFor) {
this.applyFor = applyFor;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
/** Employee.java */
package sean.study.commons.collections;
import java.util.Date;
import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;
import org.apache.commons.lang.time.DateFormatUtils;
public class Employee {
private String name;
private int age;
private Date dateJoined;
private String grade;
private double salary;
public Employee() {
}
public Employee(String name, int age, Date dateJoined, String grade, double salary) {
this.name = name;
this.age = age;
this.dateJoined = dateJoined;
this.grade = grade;
this.salary = salary;
}
public String toString() {
return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE)
.append("name", name)
.append("age", age)
.append("dateJoined", DateFormatUtils.format(dateJoined, "yyyy-MM-dd"))
.append("grade", grade)
.append("salary", salary)
.toString();
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getDateJoined() {
return dateJoined;
}
public void setDateJoined(Date dateJoined) {
this.dateJoined = dateJoined;
}
public String getGrade() {
return grade;
}
public void setGrade(String grade) {
this.grade = grade;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}
/** TransformerUsage.java */
package sean.study.commons.collections;
import java.util.Arrays;
import java.util.Collection;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.collections.Predicate;
import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.SwitchTransformer;
import org.apache.commons.lang.StringUtils;
public class TransformerUsage {
public static void main(String[] args) {
demoTransformerUsage();
}
public static void demoTransformerUsage() {
System.out.println(StringUtils.center(" demoTransformerUsage ", 40, "="));
// data setup
Applicant[] applicants = new Applicant[] {
new Applicant("Tony", 26, "Developer"),
new Applicant("Michelle", 24, "Tester"),
new Applicant("Jack", 28, "Project Manager")
};
List appList = Arrays.asList(applicants);
// predicate setup
Predicate isDeveloper = new Predicate() {
public boolean evaluate(Object obj) {
Applicant app = (Applicant) obj;
return "Developer".equalsIgnoreCase(app.getApplyFor());
}
};
Predicate isTester = new Predicate() {
public boolean evaluate(Object obj) {
Applicant app = (Applicant) obj;
return "Tester".equalsIgnoreCase(app.getApplyFor());
}
};
Predicate isPM = new Predicate() {
public boolean evaluate(Object obj) {
Applicant app = (Applicant) obj;
return "Project Manager".equalsIgnoreCase(app.getApplyFor());
}
};
Predicate[] checkApplyFor = new Predicate[] {
isDeveloper,
isTester,
isPM
};
// transformer setup
Transformer developerTransformer = new Transformer() {
public Object transform(Object obj) {
Applicant app = (Applicant) obj;
return new Employee(
app.getName(), app.getAge(), new Date(), "E4", 2000
);
}
};
Transformer testerTransformer = new Transformer() {
public Object transform(Object obj) {
Applicant app = (Applicant) obj;
return new Employee(
app.getName(), app.getAge(), new Date(), "E4", 2000
);
}
};
Transformer pmTransformer = new Transformer() {
public Object transform(Object obj) {
Applicant app = (Applicant) obj;
return new Employee(
app.getName(), app.getAge(), new Date(), "E5", 3000
);
}
};
Transformer[] transformers = new Transformer[] {
developerTransformer,
testerTransformer,
pmTransformer
};
// transform
Transformer employTransformer = new SwitchTransformer(
checkApplyFor, transformers, null
);
Collection employed = CollectionUtils.collect(appList, employTransformer);
// output
System.out.println("Applicants: ");
Iterator iter1 = appList.iterator();
while (iter1.hasNext()) {
System.out.println(iter1.next());
}
System.out.println("Employed: ");
Iterator iter2 = employed.iterator();
while (iter2.hasNext()) {
System.out.println(iter2.next());
}
System.out.println(StringUtils.repeat("=", 40));
}
}
以下是运行结果：
========= demoTransformerUsage =========
Applicants:
Applicant[name=Tony,age=26,applyFor=Developer]
Applicant[name=Michelle,age=24,applyFor=Tester]
Applicant[name=Jack,age=28,applyFor=Project Manager]
Employed:
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]
========================================
我们首先定义一组Predicate，用于在SwitchTransformer中判断采用那个具体的Transformer，这个具体的Transformer也是通过数组同时传递给SwitchTransformer的构造方法的。不同的Predicate可以有不同的实现，不同的Transformer也可以有不同的实现，因为它们之间实际上完全是相互独立的。这就使我们有效的分离了逻辑和具体业务。