序
本文主要聊一下在lombok的builder模式下，如何进行参数校验。
maven
org.projectlombok lombok 1.16.16 provided
本文基于1.16.16版本来讲
lombok的builder实例
@Data@Builderpublic class DemoModel { private String name; private int age; private int start; private int end;} 这个，是个组合的注解，具体如下
/** * Generates getters for all fields, a useful toString method, and hashCode and equals implementations that check * all non-transient fields. Will also generate setters for all non-final fields, as well as a constructor. ** Equivalent to {@code @Getter @Setter @RequiredArgsConstructor @ToString @EqualsAndHashCode}. *
* Complete documentation is found at the project lombok features page for @Data. * * @see Getter * @see Setter * @see RequiredArgsConstructor * @see ToString * @see EqualsAndHashCode * @see lombok.Value */@Target(ElementType.TYPE)@Retention(RetentionPolicy.SOURCE)public @interface Data { /** * If you specify a static constructor name, then the generated constructor will be private, and * instead a static factory method is created that other classes can use to create instances. * We suggest the name: "of", like so: * *
* public @Data(staticConstructor = "of") class Point { final int x, y; } ** * Default: No static constructor, instead the normal constructor is public. */ String staticConstructor() default "";}
@Builder会按builder模式生成一个内部类，具体使用如下
DemoModel model = DemoModel.builder() .name("hello") .age(-1) .build(); validation
那么问题来了，如果在build方法调用，返回对象之前进行参数校验呢。理想的情况当然是lombok提供一个类似jpa的@PrePersist的钩子注解呢，可惜没有。但是还是可以通过其他途径来解决，只不过需要写点代码，不是那么便捷，多lombok研究深入的话，可以自己去扩展。
@Data@Builderpublic class DemoModel { private String name; private int age; private int start; private int end; private void valid(){ Preconditions.checkNotNull(name,"name should not be null"); Preconditions.checkArgument(age > 0); Preconditions.checkArgument(start < end); } public static class InternalBuilder extends DemoModelBuilder { InternalBuilder() { super(); } @Override public DemoModel build() { DemoModel model = super.build(); model.valid(); return model; } } public static DemoModelBuilder builder() { return new InternalBuilder(); }} 这里通过继承lombok生成的builder(重写build()方法加入校验)，重写builder()静态方法，来返回自己builder。这样就大功告成了。
小结
上面的方法还不够简洁，可以考虑深入研究lombok进行扩展，实现类似jpa的@PrePersist的钩子注解，更进一步可以加入支持jsr303的validation注解。