構(gòu)建者模式：主要用于對外提供統(tǒng)一的參數(shù)封裝。

案例：Request 參數(shù)封裝。

public class Request {
    
    private String url;
    private String method;
    //私有化構(gòu)造函數(shù)
    private Request(Builder builder) {
        this.url = builder.url;
        this.method = builder.method;
    }
    //提供靜態(tài)的Buidler構(gòu)建器封裝參數(shù)
    public static Request.Builder builder() {
        return new Builder();
    } 
    
    @Override
    public String toString() {
        return "Request [url=" + url + ", method=" + method + "]";
    }

    //內(nèi)部創(chuàng)建Builder構(gòu)建器類，提供給外界設(shè)置參數(shù)
    final static class Builder{

        private String url;
        private String method;
        
        public Builder setUrl(String url) {
            this.url = url;
            return this;
        }
        public Builder setMethod(String method) {
            this.method = method;
            return this;
        }
        
        public Request build() {
            return new Request(this);
        }
    }
    //調(diào)用案例
    public static void main(String[] args) {
        Request request = Request.builder().
                setMethod("POST")
                .setUrl("http://baidu.com/") 
                .build();
        System.out.println(request.toString());
    }
}