聊聊设计模式之builder 模式

主题我们编码跟人生一样，需要有仪式感，优雅。哈哈 切入正题
先看一段代码

public ContactBusinessImpl(IContactDao contactDao, IIdMetaBusiness idMetaBusiness,
                               IDepartmentBusiness departmentBusiness,
                               IEuserBusiness euserBusiness,
                               IUserContactBusiness userContactBusiness,
                               IUserEnterpriseBusiness userEnterpriseBusiness,
                               IUserRoleBusiness userRoleBusiness,
                               IUserBusiness userBusiness,
                               ISensitiveWordBusiness sensitiveWordBusiness,
                               IProducerBusiness producerBusiness,
                               IOperationTracesBusiness operationTracesBusiness,
                               IMobileUserMappingDao mobileUserMappingDao,
                               ICommonBusiness commonBusiness) {
        this.contactDao = contactDao;
        this.idMetaBusiness = idMetaBusiness;
        this.departmentBusiness = departmentBusiness;
        this.euserBusiness = euserBusiness;
        this.userContactBusiness = userContactBusiness;
        this.userEnterpriseBusiness = userEnterpriseBusiness;
        this.userRoleBusiness = userRoleBusiness;
        this.userBusiness = userBusiness;
        this.sensitiveWordBusiness = sensitiveWordBusiness;
        this.producerBusiness = producerBusiness;
        this.operationTracesBusiness = operationTracesBusiness;
        this.mobileUserMappingDao = mobileUserMappingDao;
        this.commonBusiness = commonBusiness;
    }

这样的构造是不是让人蛋疼， 然后如果需要传入非必须属性的时候 怎么办？ 构造方法参数太多了，很容易传错。
在此我么想到了 set 如下

 public String getShoes() {
        return shoes;
    }

    public void setShoes(String shoes) {
        this.shoes = shoes;
    }

    ......

这种缺点有很多，缺点1 如果我要定义 final 的成员呢？
然后比如这样 缺点2 set 几十个的时候：

 Contact contact = new Contact();

                    contact.setContactId(rs.getString("contactId"));
                    contact.setEnterpriseId(rs.getString("enterpriseId"));
                    contact.setDepartmentId(rs.getString("departmentId"));
                    contact.setUserId(rs.getString("userId"));
                    contact.setEuserId(rs.getString("euserId"));
                    contact.setContactSort(rs.getInt("contactSort"));
                    contact.setContactLevel(rs.getInt("contactLevel"));
                    contact.setDetail(rs.getString("detail"));
                    contact.setCreateUserId(rs.getString("createUserId"));

非常的不优雅。
缺点 3 调用者可能拿到不完整状态的对象，这种方式是 先创建对象、后赋值，用户不知道什么时候拿到的对象是完整的，构建完成的。很有可能你只 set 了一两个属性就返回了，一些必要的属性没有被赋值。

回到主题： 优雅的 变种builder 模式
直接上代码：

public class ContactSingleExportBo{

    private String departmentPath;
    private String contactId;
    private String name;
    private String mobile;
    private final String departmentId;
    private String email;
    private String position;
    private String contactSort;
    private String deptVisib;
    private String euserType;
    private String otherPhone;
    private String userData;
    private String tel;
    private String contactLevel;
    private String departmentSort;
    private String departmentDepth;

    public static ContactSingleExportBo.Builder builder(String departmentId) {
        return new ContactSingleExportBo.Builder(departmentId);
    }
    // 构造 ，参数为它的静态内部类，使用静态内部类的变量一一赋值
    private ContactSingleExportBo(Builder builder) {
        departmentPath = builder.departmentPath;
        contactId = builder.contactId;
        name = builder.name;
        mobile = builder.mobile;
        departmentId = builder.departmentId;
        email = builder.email;
        position = builder.position;
        contactSort = builder.contactSort;
        deptVisib = builder.deptVisib;
        euserType = builder.euserType;
        otherPhone = builder.otherPhone;
        userData = builder.userData;
        tel = builder.tel;
        contactLevel = builder.contactLevel;
        departmentSort = builder.departmentSort;
        departmentDepth = builder.departmentDepth;
    }

    //的静态内部类，成员变量和 本类 的一致
    public static final class Builder {
        private String departmentPath;
        private String contactId;
        private String name;
        private String mobile;
        private final String departmentId; //必选 初始化在构造器中
        private String email;
        private String position;
        private String contactSort;
        private String deptVisib;
        private String euserType;
        private String otherPhone;
        private String userData;
        private String tel;
        private String contactLevel;
        private String departmentSort;
        private String departmentDepth;

        public Builder(String departmentId) {
            this.departmentId = departmentId;
        }

        public Builder departmentPath(String val) {
            departmentPath = val;
            return this;
        }

        public Builder contactId(String val) {
            contactId = val;
            return this;
        }

        public Builder name(String val) {
            name = val;
            return this;
        }

        public Builder mobile(String val) {
            mobile = val;
            return this;
        }


        public Builder email(String val) {
            email = val;
            return this;
        }

        public Builder position(String val) {
            position = val;
            return this;
        }

        public Builder contactSort(String val) {
            contactSort = val;
            return this;
        }

        public Builder deptVisib(String val) {
            deptVisib = val;
            return this;
        }

        public Builder euserType(String val) {
            euserType = val;
            return this;
        }

        public Builder otherPhone(String val) {
            otherPhone = val;
            return this;
        }

        public Builder userData(String val) {
            userData = val;
            return this;
        }

        public Builder tel(String val) {
            tel = val;
            return this;
        }

        public Builder contactLevel(String val) {
            contactLevel = val;
            return this;
        }

        public Builder departmentSort(String val) {
            departmentSort = val;
            return this;
        }

        public Builder departmentDepth(String val) {
            departmentDepth = val;
            return this;
        }

        public ContactSingleExportBo build() {
            return new ContactSingleExportBo(this);
        }
    }
}

看起来代码很多， 其实都可以自动生成，

还有 IEDA 可以使用插件 直接注解 ，更优雅，

/**
 *  删除文档元数据
 */
@Getter
@Setter
@Builder
public class DocNodeLocationMeta {
    @NotNull(message = "文档类型不能为null")
    private String indexType;                      // 索引类型
    @NotNull(message = "分片信息不能为null")
    private String indexShardingData;              // 分片字段
    @NotNull(message = "文档标识符不能为null")
    private String docIdentifier;                  // 文档标识符
    private String routingData;                    // 路由数据

}

是不是很简单了？ 注解自行了解插件lombok
可以看到

然后我们来看看它的链式调用：

这里灰常优雅 ，先赋值，后创建对象，最终调用 build() 方法才创建了构建类的对象，保证了状态的完整性。

总结：
经典的 Builder 模式定义为：
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。