Commons Collections - Transformer

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)
"name", name)
"age", age)
"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;
    }
 
}
 
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)
"name", name)
"age", age)
"dateJoined", DateFormatUtils.format(dateJoined, "yyyy-MM-dd"))
"grade", grade)
"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;
    }
 
} 
 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() {
 
" 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
        };