JavaBean之Builder模式

静态工厂和构造器

重载构造函数，分别包含多个不同的参数

无法很好地扩展到大量的可选参数

JavaBean方式

调用一个无参构造函数来创建对象，然后通过setter方法来设置必要参数

对象构造过程被分割到了几个调用，构造过程中可能导致JavaBean处于不一致的状态，类无法通过检验构造器参数的有效性来保证一致性

Builder模式

不直接生成想要的对象，通过调用构造器（或静态工厂），得到builder对象，客户端在builder对象上调用类似setter方法，来设置每个相关的可选参数，最后，再调用build方法来生成不可变对象

public class Person {    @Override    public String toString() {        return "Person{" +                "name='" + name + '\'' +                ", address='" + address + '\'' +                ", firstName='" + firstName + '\'' +                ", lastName='" + lastName + '\'' +                '}';    }    private String name;    private String address;    private String firstName;    private String lastName;    private Person(String name, String address, String firstName, String lastName) {        this.address = address;        this.name = name;        this.lastName = lastName;        this.firstName = firstName;    }    public static Builder builder() {        return new Builder();    }    public static class Builder {        private String name;        private String address;        private String firstName;        private String lastName;        public Builder name(final String name) {            this.name = name;            return this;        }        public Builder address(final String address) {            this.address = address;            return this;        }        public Builder lastName(final String lastName) {            this.lastName = lastName;            return this;        }        public Builder firstName(final String firstName) {            this.firstName = firstName;            return this;        }        public Person build() {            return new Person(name, address, firstName, lastName);        }    }}

客户端调用

        Person p = new Person.Builder().address("上海").firstName("三").lastName("张").name("欧阳").build();        System.out.println(p);        Person person = Person.builder().address("上海").firstName("三").lastName("张").name("欧阳").build();        System.out.println(person);

如果我们使用IDE，我们可以直接使用Lombok插件的@Builder注解，仅需声明类属性

@Builder@ToStringpublic class LombokPerson {    private String name;    private String address;    private String firstName;    private String lastName;}

查看生成的class源码

public class LombokPerson {    private String name;    private String address;    private String firstName;    private String lastName;    @ConstructorProperties({"name", "address", "firstName", "lastName"})    LombokPerson(String name, String address, String firstName, String lastName) {        this.name = name;        this.address = address;        this.firstName = firstName;        this.lastName = lastName;    }    public static LombokPerson.LombokPersonBuilder builder() {        return new LombokPerson.LombokPersonBuilder();    }    public String toString() {        return "LombokPerson(name=" + this.name + ", address=" + this.address + ", firstName=" + this.firstName + ", lastName=" + this.lastName + ")";    }    public static class LombokPersonBuilder {        private String name;        private String address;        private String firstName;        private String lastName;        LombokPersonBuilder() {        }        public LombokPerson.LombokPersonBuilder name(String name) {            this.name = name;            return this;        }        public LombokPerson.LombokPersonBuilder address(String address) {            this.address = address;            return this;        }        public LombokPerson.LombokPersonBuilder firstName(String firstName) {            this.firstName = firstName;            return this;        }        public LombokPerson.LombokPersonBuilder lastName(String lastName) {            this.lastName = lastName;            return this;        }        public LombokPerson build() {            return new LombokPerson(this.name, this.address, this.firstName, this.lastName);        }        public String toString() {            return "LombokPerson.LombokPersonBuilder(name=" + this.name + ", address=" + this.address + ", firstName=" + this.firstName + ", lastName=" + this.lastName + ")";        }    }}

客户端调用：

        LombokPerson lombokPerson = LombokPerson.builder().address("上海").firstName("三").lastName("张").name("欧阳").build();        System.out.println(lombokPerson);

https://dzone.com/articles/too-many-parameters-java-1