在org.apache.commons.lang.builder包中一共有7个类，用于帮助实现Java对象的一些基础的方法，如compareTo(), equals(), hashCode(), toString()等。他们分别是：
CompareToBuilder – 用于辅助实现Comparable.compareTo(Object)方法；
EqualsBuilder – 用于辅助实现Object.equals()方法；
HashCodeBuilder – 用于辅助实现Object.hashCode()方法；
ReflectionToStringBuilder – 使用反射机制辅助实现Object.toString()方法；
ToStringBuilder – 用于辅助实现Object.toString()方法；
StandardToStringStyle – 辅助ToStringBuilder控制标准格式；
ToStringStyle – 辅助ToStringBuilder控制输出格式。
我们来看下面的例子来学习这些类的使用：
package org.apache.commons.lang.builder;
import java.util.Date;
import org.apache.commons.lang.builder.CompareToBuilder;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.ReflectionToStringBuilder;
import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;
import org.apache.commons.lang.builder.StandardToStringStyle;
public class BuilderTest 
{
public static void main(String[] args) {
Person person1 = new Person("郑致力", 32, new Date());
Person person2 = new Person("高婕", 27, new Date());
System.out.println("person1's info: " + person1);
System.out.println("person2's info: " + person2);
System.out.println("person1's hash code: " + person1.hashCode());
System.out.println("person2's hash code: " + person2.hashCode());
System.out.println("person1 equals person2? " + person1.equals(person2));
System.out.println("--------------More String Style of Object ------------------------------------");
System.out.println("person1's info: " + person1.toString2(ToStringStyle.MULTI_LINE_STYLE));
System.out.println("person1's info: " + person1.toString2(ToStringStyle.NO_FIELD_NAMES_STYLE));
System.out.println("person1's info: " + person1.toString2(ToStringStyle.SHORT_PREFIX_STYLE));
System.out.println("person1's info: " + person1.toString2(ToStringStyle.SIMPLE_STYLE));
System.out.println("person1's info: " + person1.toString2(new StandardToStringStyle()));
}
}
class Person implements Comparable {
private String name;
private int age;
private Date dateJoined;
public Person() {
};
public Person(String name, int age, Date dateJoined) {
this.name = name;
this.age = age;
this.dateJoined = dateJoined;
}
public int compareTo(Object o) {
if (!(o instanceof Person)) {
return -1;
}
Person other = (Person) o;
return new CompareToBuilder().append(name, other.getName()).append(age,
other.getAge()).append(dateJoined, other.getDateJoined())
.toComparison();
}
public boolean equals(Object o) {
if (!(o instanceof Person)) {
return false;
}
Person other = (Person) o;
return new EqualsBuilder().append(name, other.getName()).append(age,
other.getAge()).append(dateJoined, other.getDateJoined())
.isEquals();
}
public int hashCode() {
return new HashCodeBuilder().append(name).append(age)
.append(dateJoined).toHashCode();
}
public String toString() {
return new ToStringBuilder(this).append("name", name)
.append("age", age).append("dateJoined", dateJoined).toString();
}
public String toString2(ToStringStyle style) {
ToStringStyle _style = ToStringStyle.DEFAULT_STYLE;
if (null != style) {
_style = style;
}
return new ToStringBuilder(this, _style).append("name", name)
.append("age", age).append("dateJoined", dateJoined).toString();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
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;
}
}
这些builder用起来很简单，只要new一个实例，append需要参与的信息，然后加上toComparison、isEquals、toHashCode、toString结尾就可以了。如果不需要使用append指定信息，则可直接使用反射机制进行自动化实现，如下面的Student类：
class Student extends Person {
private int grad;
public Student() {super();}
public Student(String name, int age, Date dateJoined, int grad) {
super(name, age, dateJoined);
this.grad = grad;
}
public int compareTo(Object o) {
return CompareToBuilder.reflectionCompare(this, o);
}
public boolean equals(Object o) {
return EqualsBuilder.reflectionEquals(this, o);
}
public int hashCode() {
return HashCodeBuilder.reflectionHashCode(this);
}
public String toString() {
return ReflectionToStringBuilder.toString(this);
}
}
这里需要补充一点，对于ToStringStyle类，代码中已经内置了5种，分别为ToStringStyle.DEFAULT_STYLE、ToStringStyle.MULTI_LINE_STYLE、ToStringStyle.NO_FIELD_NAMES_STYLE、ToStringStyle.SHORT_PREFIX_STYLE、ToStringStyle.SIMPLE_STYLE。不知道为什么，这5种内置类的实现都被定义成了private static final类了。所以如果上述5种类不能满足你的要求的话，想继承他们是不可能的。所以你需要创建StandardToStringStyle一个实例，然后调用它的方法来实现自定义的格式。在StandardToStringStyle的单元测试代码中，是这样调用的：
private static final StandardToStringStyle STYLE = new StandardToStringStyle();
static {
STYLE.setUseShortClassName(true);
STYLE.setUseIdentityHashCode(false);
STYLE.setArrayStart("[");
STYLE.setArraySeparator(", ");
STYLE.setArrayEnd("]");
STYLE.setNullText("%NULL%");
STYLE.setSizeStartText("%SIZE=");
STYLE.setSizeEndText("%");
STYLE.setSummaryObjectStartText("%");
STYLE.setSummaryObjectEndText("%");
}