Lambda表达式和通用Builder构建对象

目的是增加在创建对象时代码的可读性

 

（1）实体

public class User {

    private String username;

    private String password;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

 

（2）用来构建对象的通用Builder类

public class Builder<T> {
    
    private final Supplier<T> instantiator;
    private List<Consumer<T>> modifiers = new ArrayList<>();
    
    public Builder(Supplier<T> instantiator) {
        this.instantiator = instantiator;
    }
    
    public static <T> Builder<T> of(Supplier<T> instantiator) {
        return new Builder<>(instantiator);
    }
    
    public <P1> Builder<T> with(Consumer1<T, P1> consumer, P1 p1) {
        Consumer<T> c = instance -> consumer.accept(instance, p1);
        modifiers.add(c);
        return this;
    }
    
    public <P1, P2> Builder<T> with(Consumer2<T, P1, P2> consumer, P1 p1, P2 p2) {
        Consumer<T> c = instance -> consumer.accept(instance, p1, p2);
        modifiers.add(c);
        return this;
    }
    
    public <P1, P2, P3> Builder<T> with(Consumer3<T, P1, P2, P3> consumer, P1 p1, P2 p2, P3 p3) {
        Consumer<T> c = instance -> consumer.accept(instance, p1, p2, p3);
        modifiers.add(c);
        return this;
    }
    
    public T build() {
        T value = instantiator.get();
        modifiers.forEach(modifier -> modifier.accept(value));
        modifiers.clear();
        return value;
    }
    
    /**
     * 1 参数 Consumer
     */
    @FunctionalInterface
    public interface Consumer1<T, P1> {
        void accept(T t, P1 p1);
    }
    
    /**
     * 2 参数 Consumer
     */
    @FunctionalInterface
    public interface Consumer2<T, P1, P2> {
        void accept(T t, P1 p1, P2 p2);
    }
    
    /**
     * 3 参数 Consumer
     */
    @FunctionalInterface
    public interface Consumer3<T, P1, P2, P3> {
        void accept(T t, P1 p1, P2 p2, P3 p3);
    }
    
}

 

（3）测试

public class BuilderTest {

    public static void main(String args[]){
        //构建对象
        User user = Builder.of(User::new)
                .with(User::setUsername, "username")
                .with(User::setPassword, "password")
                .build();
        System.out.println(user);
    }
}

 

（4）结果