一.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。如果一个对象具有复杂的内部结构或者内部属性本身相互依赖(有顺序要求)，甚至对象中的某些属性的创建也有一个很复杂的过程，就可以使用建造者模式
二.UML类图
三.具体代码
- 业务代码
public class Product {
private String part1;
private String part2;
public Product(String part1, String part2) {
this.part1 = part1;
this.part2 = part2;
}
@Override
public String toString() {
return "Product{" +
"part1='" + part1 + '\'' +
", part2='" + part2 + '\'' +
'}';
}
}
//控制每个部件的具体创建
interface Builder {
void buildPart1(String part1);
void buildPart2(String part2);
Product build();
}
class ChinaBuilder implements Builder{
private String part1;
private String part2;
@Override
public void buildPart1(String part1) {
this.part1 = "国产" + part1;
}
@Override
public void buildPart2(String part2) {
this.part2 = "国产" + part2;
}
@Override
public Product build() {
return new Product(part1, part2);
}
}
//控制组装部件的顺序
class Director{
private Builder builder;
public Director(Builder builder) {
this.builder = builder;
}
public Product construct(String part1, String part2){
builder.buildPart1(part1);
builder.buildPart2(part2);
return builder.build();
}
}
- 测试代码
public class BuilderTest {
public static void main(String[] args) {
Director director = new Director(new ChinaBuilder());
Product product = director.construct("传感器", "芯片");
System.out.println(product); //Product{part1='国产传感器', part2='国产芯片'}
}
}
四.lombok的@Builder注解（拓展）
我们先以静态内部类的方式实现简单场景下的建造者模式(以优雅的链式调用代替set)
- 业务代码
public class Product {
private String part1;
private String part2;
public Product(String part1, String part2) {
this.part1 = part1;
this.part2 = part2;
}
@Override
public String toString() {
return "Product{" +
"part1='" + part1 + '\'' +
", part2='" + part2 + '\'' +
'}';
}
static class Builder {
private String part1;
private String part2;
public Builder part1(String part1) {
this.part1 = part1;
return this;
}
public Builder part2(String part2) {
this.part2 = part2;
return this;
}
public Product build(){
return new Product(part1, part2);
}
}
}
- 测试类
public class ProductTest {
public static void main(String[] args) {
Product product = new Product.Builder().part1("传感器").part2("芯片").build();
System.out.println(product); //Product{part1='传感器', part2='芯片'}
}
}
- 下面看看lombok的@Builder注解的实现
业务代码
@Builder
public class Product {
private String part1;
private String part2;
}
在IDEA中打开Product.class文件，可以看出实际就是使用的简单场景的建造者模式
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//
package com.designpattern.create.builder.lombok;
public class Product {
private String part1;
private String part2;
Product(String part1, String part2) {
this.part1 = part1;
this.part2 = part2;
}
public static Product.ProductBuilder builder() {
return new Product.ProductBuilder();
}
public static class ProductBuilder {
private String part1;
private String part2;
ProductBuilder() {
}
public Product.ProductBuilder part1(String part1) {
this.part1 = part1;
return this;
}
public Product.ProductBuilder part2(String part2) {
this.part2 = part2;
return this;
}
public Product build() {
return new Product(this.part1, this.part2);
}
public String toString() {
return "Product.ProductBuilder(part1=" + this.part1 + ", part2=" + this.part2 + ")";
}
}
}
五.在Spring中的应用
org.springframework.web.servlet.mvc.method.RequestMappingInfo.DefaultBuilder