介绍
建造者模式（Builder Pattern）使用多个简单的对象一步一步构建成一个复杂的对象。这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方式。
一个 Builder 类会一步一步构造最终的对象。该 Builder 类是独立于其他对象的。
特点
将一个复杂的构建与其表示相分离，使得同样的构建过程可以创建不同的表示。主要解决在软件系统中，有时候面临着”一个复杂对象”的创建工作，其通常由各个部分的子对象用一定的算法构成；由于需求的变化，这个复杂对象的各个部分经常面临着剧烈的变化，但是将它们组合在一起的算法却相对稳定。
角色
- Product：表示被构造的复杂对象。
- builder：为创建一个产品对象的各个部件指定抽象接口。
- ConcreteBuilder：实现Builder的接口以构造和装配该产品的各个部件，定义并明确它所创建的表示，并提供一个检索产品的接口。
- Director：构造一个使用Builder接口的对象。
优缺点
优点：
- 建造者独立，易扩展；
- 便于控制细节风险。
缺点：
产品必须有共同点，范围有限制。
如内部变化复杂，会有很多的建造类。
使用场景
- 需要生成的对象具有复杂的内部结构。
- 需要生成的对象内部属性本身相互依赖。
注意事项：与工厂模式的区别是：建造者模式更加关注与零件装配的顺序。
举例
创建Product
/**
* 具体的产品 Product
* Created by ZhangYW on 2018/4/20.
*/
public class Person {
private String head;
private String body;
private String foot;
public String getHead() {
return head;
}
public void setHead(String head) {
this.head = head;
}
public String getBody() {
return body;
}
public void setBody(String body) {
this.body = body;
}
public String getFoot() {
return foot;
}
public void setFoot(String foot) {
this.foot = foot;
}
}创建builder
/**
* 抽象建造 builder
* Created by ZhangYW on 2018/4/20.
*/
public interface Builder {
void buildHead();
void buildBody();
void buildFoot();
Person buildPerson();//组装
}创建ConcreteBuilder
/**
* 具体的建造 ConcreteBuilder
* Created by ZhangYW on 2018/4/20.
*/
public class ConcreteBuilder implements Builder{
private Person person;
public ConcreteBuilder(){
person = new Person();
}
@Override
public void buildHead() {
person.setHead("建造头部");
}
@Override
public void buildBody() {
person.setBody("建造身体");
}
@Override
public void buildFoot() {
person.setFoot("建造四肢");
}
@Override
public Person buildPerson() {
return person;
}
}创建Director
/**
* 导演者 Director
* Created by ZhangYW on 2018/4/20.
*/
public class Director {
public Person constructPerson(Builder builder) {
builder.buildHead();
builder.buildBody();
builder.buildFoot();
return builder.buildPerson();
}
}测试类
/**
* 测试类
* Created by ZhangYW on 2018/4/20.
*/
public class Test {
public static void main(String[] args) {
Director director = new Director();
Person person = director.constructPerson(new ConcreteBuilder());
System.out.println(person.getHead());
System.out.println(person.getBody());
System.out.println(person.getFoot());
}
}上面是标准的建造者模式，不怎么好理解，下面举个常见的：
创建Product
public class Person {
private String name;
private int age;
public Person(String name,int age) {
this.name = name;
this.age = age;
}
}创建Builder
public class Builder {
private String name;
private int age;
public Builder setName(String name) {
this.name = name;
return this;
}
public Builder setAge(int age) {
this.age = age;
return this;
}
public Person create() {
return new Person(name, age);
}
}测试类
public class Test {
public static void main(String[] args) {
Builder builder = new Builder();
builder.setName("zhangsan");
builder.setAge(20);
Perons person = builder.create();
}
}还有更清晰的一种：
/**
* Created by ZhangYW on 2018/4/20.
*/
public class MyPerson {
private String name;
private int age;
private double height;
private double weight;
private MyPerson(Builder builder) {
this.name=builder.name;
this.age=builder.age;
this.height=builder.height;
this.weight=builder.weight;
}
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 double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
static class Builder{
private String name;
private int age;
private double height;
private double weight;
public Builder name(String name){
this.name=name;
return this;
}
public Builder age(int age){
this.age=age;
return this;
}
public Builder height(double height){
this.height=height;
return this;
}
public Builder weight(double weight){
this.weight=weight;
return this;
}
public MyPerson build(){
return new MyPerson(this);
}
}
}测试类
/**
* 测试类
* Created by ZhangYW on 2018/4/20.
*/
public class Test {
MyPerson.Builder builder = new MyPerson.Builder();
MyPerson myPerson = builder
.name("zhangsan")
.age(20)
.build();
}
}补充：
android中有很多地方用到了建造者模式，例如AlertDialog、Notification、第三方网络请求框架okhttp等