05-设计模式——建造者（生成器）模式

设计模式——建造者（生成器）模式

生成器Builder：

封装一个对象的构造过程，并允许按步骤构造。

模式定义：

将一个复杂对象的创建与他的表示分离，使得同样的构建过程可以创建不同的表示

应用场景：

1. 需要生成的对象具有复杂的内部结构
2. 需要生成的对象内部属性本身相互依赖
3. 与不可变对象配合使用

优点：

1. 建造者独立、易扩展
2. 便于控制细节风险

V1复杂版本

package com.example.designpatterns.builder.v1;
 
import lombok.Data;
 
/**
 * @program: DesignPatterns
 * @description: 构造者模式 V1-复杂版本
 * @author: Coder_Pan
 * @create: 2022-04-13 10:01
 **/
 
public class BuilderTest {
    public static void main(String[] args) {
        DefaultConcreateProductBuilder defaultConcreateProductBuilder = new DefaultConcreateProductBuilder();
        Director director = new Director(defaultConcreateProductBuilder);
        Product product = director.makeProduct("螺蛳粉", "panpan", "p1", "p2", "p3", "p4");
        System.out.println(product);
        System.out.println("-------------------------------------------------------------------");
        NewConcreateProductBuilder newBuilder = new NewConcreateProductBuilder();
        Director director1 = new Director(newBuilder);
        Product product1 = director.makeProduct("new螺蛳粉", "panpan", "p1", "p2", "p3", "p4");
        System.out.println(product1);
    }
}
 
/**
 * 定义构建者模式
 */
interface ProductBuilder {
    /**
     * 创建对象
     * @return
     */
    Product build();
    /**
     * builderProductName
     * @param productName
     */
    void builderProductName(String productName);
    /**
     * builderCompanyName
     * @param companyName
     */
    void builderCompanyName(String companyName);
 
    /**
     * buildPart1
     * @param part1
     */
    void buildPart1(String part1);
 
    /**
     * buildPart2
     * @param part2
     */
    void buildPart2(String part2);
 
    /**
     * buildPart3
     * @param part3
     */
    void buildPart3(String part3);
 
    /**
     * buildPart4
     * @param part4
     */
    void buildPart4(String part4);
 
}
 
/**
 * 创建构造者模式实现类
 *
 * 默认  =>  Default
 */
class  DefaultConcreateProductBuilder implements ProductBuilder {
    /**
     * 若干个属性
     */
    private String productName;
    private String companyName;
    private String part1;
    private String part2;
    private String part3;
    private String part4;
 
    @Override
    public Product build() {
        return new Product(this.productName,this.companyName,this.part1,this.part2,this.part3,this.part4);
    }
 
    @Override
    public void builderProductName(String productName) {
        this.productName = productName;
    }
 
    @Override
    public void builderCompanyName(String companyName) {
        this.companyName = companyName;
    }
 
    @Override
    public void buildPart1(String part1) {
        this.part1 = part1;
    }
 
    @Override
    public void buildPart2(String part2) {
        this.part2 = part2;
    }
 
    @Override
    public void buildPart3(String part3) {
        this.part3 = part3;
    }
 
    @Override
    public void buildPart4(String part4) {
        this.part4 = part4;
    }
}
 
/**
 * 另外一个产品构造器
 *
 * 可以使用另外一种建造方式
 */
class  NewConcreateProductBuilder implements ProductBuilder {
    /**
     * 若干个属性
     */
    private String productName;
    private String companyName;
    private String part1;
    private String part2;
    private String part3;
    private String part4;
 
    @Override
    public Product build() {
        return new Product(this.productName,this.companyName,this.part1,this.part2,this.part3,this.part4);
    }
 
    @Override
    public void builderProductName(String productName) {
        this.productName = productName;
    }
 
    @Override
    public void builderCompanyName(String companyName) {
        this.companyName = companyName;
    }
 
    @Override
    public void buildPart1(String part1) {
        this.part1 = part1;
    }
 
    @Override
    public void buildPart2(String part2) {
        this.part2 = part2;
    }
 
    @Override
    public void buildPart3(String part3) {
        this.part3 = part3;
    }
 
    @Override
    public void buildPart4(String part4) {
        this.part4 = part4;
    }
}
/**
 * 定义一个导向器
 */
class Director {
 
    private ProductBuilder builder;
 
    /**
     * 通过构造函数将构造者传入
     *
     * @param builder
     */
    public Director(ProductBuilder builder){
        this.builder = builder;
    }
    /**
     * 控制构造顺序
     */
    public Product makeProduct(String productName, String companyName, String part1, String part2, String part3, String part4){
        builder.builderProductName(productName);
        builder.builderCompanyName(companyName);
        builder.buildPart1(part1);
        builder.buildPart2(part2);
        builder.buildPart3(part3);
        builder.buildPart4(part4);
        Product build = builder.build();
        return build;
    }
 
}
/**
 * 定义一个产品对象  => Product
 *
 * 通过lombok简化get、set方法
 */
@Data
class Product {
    /**
     * 若干个属性
     */
    private String productName;
    private String companyName;
    private String part1;
    private String part2;
    private String part3;
    private String part4;
    //.....若干个属性
 
    /**
     * 空参构造
     */
    public Product(){
    }
    /**
     * 全参构造
     * @param productName
     * @param companyName
     * @param part1
     * @param part2
     * @param part3
     * @param part4
     */
    public Product(String productName, String companyName, String part1, String part2, String part3, String part4){
        this.productName = productName;
        this.companyName = companyName;
        this.part1 = part1;
        this.part2 = part2;
        this.part3 = part3;
        this.part4 = part4;
    }
}

V2-精简版本

package com.example.designpatterns.builder.v2;
 
import lombok.Data;
 
/**
 * @program: DesignPatterns
 * @description: 构造者模式 V2-精简版本 ==>  链式编程
 * @author: Coder_Pan
 * @create: 2022-04-13 10:33
 **/
public class ProductTestV2 {
    public static void main(String[] args) {
        Product product = new Product.Builder()
                //链式调用.....
                .productName("XXXX")
                .companyName("123p_p")
                .part1("1111")
                .part2("2222")
                .part3("3333")
                .part4("4444")
                .build();//通过build，最终生成实例
        System.out.println(product);
    }
}
/**
 * 定义一个产品对象  => Product
 *
 * 通过lombok简化get、set方法
 */
@Data
class Product {
    /**
     * 若干个属性
     * final  =>  在构建的时候才会将真实的值传入，传入之后就不能再次修改了.....
     */
    private final String productName;
    private final String companyName;
    private final String part1;
    private final String part2;
    private final String part3;
    private final String part4;
    //.....若干个属性
 
    /**
     * 全参构造
     * @param productName
     * @param companyName
     * @param part1
     * @param part2
     * @param part3
     * @param part4
     */
    public Product(String productName, String companyName, String part1, String part2, String part3, String part4){
        this.productName = productName;
        this.companyName = companyName;
        this.part1 = part1;
        this.part2 = part2;
        this.part3 = part3;
        this.part4 = part4;
    }
    /**
     * 定义静态内部构造器
     *
     */
    static class Builder {
        /**
         * 若干个属性
         */
        private String productName;
        private String companyName;
        private String part1;
        private String part2;
        private String part3;
        private String part4;
 
        public Builder productName(String productName){
            this.productName = productName;
            return this;
        }
        public Builder companyName(String companyName){
            this.companyName = companyName;
            return this;
        }
        public Builder part1(String part1){
            this.part1 = part1;
            return this;
        }
        public Builder part2(String part2){
            this.part2 = part2;
            return this;
        }
        public Builder part3(String part3){
            this.part3 = part3;
            return this;
        }
        public Builder part4(String part4){
            this.part4 = part4;
            return this;
        }
 
        /**
         *
         * @return product实例
         */
        Product build(){
            //校验操作
            Product product = new Product(this.productName, this.companyName, this.part1, this.part2, this.part3, this.part4);
            return product;
        }
    }
}

StringBuilder

以下是一个简易的 StringBuilder 实现，参考了 JDK 1.8 源码。

public class AbstractStringBuilder {
    protected char[] value;
	protected int count;
 
public AbstractStringBuilder(int capacity) {
    count = 0;
    value = new char[capacity];
}
 
public AbstractStringBuilder append(char c) {
    ensureCapacityInternal(count + 1);
    value[count++] = c;
    return this;
}
 
private void ensureCapacityInternal(int minimumCapacity) {
    // overflow-conscious code
    if (minimumCapacity - value.length > 0)
        expandCapacity(minimumCapacity);
}
 
void expandCapacity(int minimumCapacity) {
    int newCapacity = value.length * 2 + 2;
    if (newCapacity - minimumCapacity < 0)
        newCapacity = minimumCapacity;
    if (newCapacity < 0) {
        if (minimumCapacity < 0) // overflow
            throw new OutOfMemoryError();
        newCapacity = Integer.MAX_VALUE;
    }
    value = Arrays.copyOf(value, newCapacity);
	}
}

public class StringBuilder extends AbstractStringBuilder {
    public StringBuilder() {
        super(16);
    }
 
    @Override
    public String toString() {
        // Create a copy, don't share the array
        return new String(value, 0, count);
    }
}

public class Client {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        final int count = 26;
        for (int i = 0; i < count; i++) {
            sb.append((char) ('a' + i));
        }
        System.out.println(sb.toString());
    }
}

JDK

• java.lang.StringBuilder
• java.nio.ByteBuffer
• java.lang.StringBuffer
• java.lang.Appendable
• [Apache Camel builders](