设计模式-建造者模式
概念
将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示
用户只需指定需要建造的类型就可以得到他们，建造过程及细节不需要知道
类型：创建型
使用场景
- 如果一个对象有非常复杂的内部结构(很多属性)
- 把对象创建和使用分离
优点
封装性好，创建和使用分离
扩展性好，建造类之间独立，一定程度上解耦
-
便于控制细节风险
建造者是独立的，因此可以对建造过程逐步细化，不影响其他模块
缺点
- 产生多余的Builder对象
- 产品内部发生变化，建造者需要修改
UML
建造者模式UML.png
-
Product 产品类
public class Product { public void doSomething() { //... } } -
Builder抽象建造者
public abstract class Builder { //设置产品的不同部分，以获得不同的产品 public abstract void setPart(); //构建产品 pubilc abstract Product buildProduct(); } -
ConcreteBuilder具体建造者
public class ConcreteProduct extends Builder { private Product product = new Product(); //设置产品零件 pubilc void setPart() { //设置Product相关属性等 } //组件一个产品 public Product buildProduct() { return product; } } -
Director导演类
导演类起到了封装作用，避免了高层模块深入到建造者内部的实现。如果建造者模式比较庞大，导演类可以有多个
public class Director { private Builder builder = new ConcreteProduct(); //构建不同的产品 public Product getAProduct() { //设置不同的零件，可以产生不同的产品 builder.setPart(); return builder.buildProduct(); } }
实例
我们以组装电脑为例：组装电脑需要主板、CPU、内存、硬盘等等
UML
实例UML.png
产品类
public class Computer {
//各个组件 与 电脑 是整体与部分关系；该场景主要是建造者模式；组件就不在抽象，均以Object为类型
private Object cpu;
private Object mainBoard;
private Object memory;
private Object disk;
private Object power;
public Object getCpu() {
return cpu;
}
public void setCpu(Object cpu) {
this.cpu = cpu;
}
public Object getMainBoard() {
return mainBoard;
}
public void setMainBoard(Object mainBoard) {
this.mainBoard = mainBoard;
}
public Object getMemory() {
return memory;
}
public void setMemory(Object memory) {
this.memory = memory;
}
public Object getDisk() {
return disk;
}
public void setDisk(Object disk) {
this.disk = disk;
}
public Object getPower() {
return power;
}
public void setPower(Object power) {
this.power = power;
}
@Override
public String toString() {
return "{" +
"cpu:" + cpu + ", " +
"mainBoard:" + mainBoard + ", " +
"memory:" + memory + ", " +
"disk:" + disk + ", " +
"power:" + power +
"}";
}
}
抽象建造者
public interface IComputerBuilder {
void buildCpu(Object cpu);
void buildMainBoard(Object mainBoard);
void buildMemory(Object memory);
void buildDisk(Object disk);
void buildPower(Object power);
Computer getComputer();
}
具体构建者
public class ComputerBuilderImpl implements IComputerBuilder {
private Computer computer = new Computer();
@Override
public void buildCpu(Object cpu) {
computer.setCpu(cpu);
}
@Override
public void buildMainBoard(Object mainBoard) {
computer.setMainBoard(mainBoard);
}
@Override
public void buildMemory(Object memory) {
computer.setMemory(memory);
}
@Override
public void buildDisk(Object disk) {
computer.setDisk(disk);
}
@Override
public void buildPower(Object power) {
computer.setPower(power);
}
@Override
public Computer getComputer() {
return computer;
}
}
导演类
public class Director {
public void construct(IComputerBuilder builder) {
builder.buildCpu("i5");
builder.buildDisk("500G");
builder.buildMainBoard("hp-MainBoard");
builder.buildMemory("16G");
builder.buildPower("hp-Power");
}
}
使用场景
public class Client {
// 一个消费者向电脑门店购买电脑；电脑商家组件电脑后，卖给消费者
public static void main(String[] args) {
IComputerBuilder builder = new ComputerBuilderImpl();
Director director = new Director();
director.construct(builder);
Computer computer = builder.getComputer();
System.out.println(computer);
}
}
源码案例
-
StringBuilder （源码做了提取）
abstract class AbstractStringBuilder implements Appendable, CharSequence { char[] value; int count; public AbstractStringBuilder append(String str) { if (str == null) return appendNull(); int len = str.length(); ensureCapacityInternal(count + len); //将 value 插入到 str 对应的char数组中；从0开始插入 str.getChars(0, len, value, count); count += len; //返回自己 return this; } }
public final class StringBuilder extends AbstractStringBuilder
implements java.io.Serializable, CharSequence {
//组织产品零件
@Override
public StringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
//组织产品零件
@Override
public StringBuilder append(String str) {
super.append(str);
return this;
}
//构建出产品
@Override
public String toString() {
// Create a copy, don't share the array
return new String(value, 0, count);
}
}
-
ES-BulkProcessor (静态内部类方式)
public class BulkProcessor implements Closeable { //...无关代码 //构造器，该构造器 不是 public，由静态内部类构建 BulkProcessor(Client client, BackoffPolicy backoffPolicy, Listener listener, @Nullable String name, int concurrentRequests, int bulkActions, ByteSizeValue bulkSize, @Nullable TimeValue flushInterval) { //属性设置 this.... = ... } //静态内部类构建 对象 public static class Builder { private final Client client; private final Listener listener; private String name; private int concurrentRequests = 1; private int bulkActions = 1000; private ByteSizeValue bulkSize = new ByteSizeValue(5, ByteSizeUnit.MB); private TimeValue flushInterval = null; private BackoffPolicy backoffPolicy = BackoffPolicy.exponentialBackoff(); public Builder(Client client, Listener listener) { this.client = client; this.listener = listener; } public Builder setName(String name) { this.name = name; return this; } public Builder setConcurrentRequests(int concurrentRequests) { this.concurrentRequests = concurrentRequests; return this; } public Builder setBulkActions(int bulkActions) { this.bulkActions = bulkActions; return this; } public Builder setBulkSize(ByteSizeValue bulkSize) { this.bulkSize = bulkSize; return this; } public Builder setFlushInterval(TimeValue flushInterval) { this.flushInterval = flushInterval; return this; } public Builder setBackoffPolicy(BackoffPolicy backoffPolicy) { this.backoffPolicy = backoffPolicy; return this; } public BulkProcessor build() { return new BulkProcessor(client, backoffPolicy, listener, name, concurrentRequests, bulkActions, bulkSize, flushInterval); } } }
