目录
@NoArgsConstructor/@RequiredArgsConstructor/@AllArgsConstructor
lombok简介
lombok是一个java类库，能够自动植入开发者的编译器来辅助java开发。使用lombok，可以使用一个注解来代替getter等方法的编写。使用起来非常简单，maven pom.xml文件中加入如下依赖，
<dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.12</version> </dependency>
在实体类上加上注解@Data
@Data
public class Employee{
private Long id;
private String name;
private String department;
private Long number;
}
测试代码如下：
从图片中可以看出有编译错误代码，但是执行这个测试用例可以成功。
IDEA配置lombok
IDEA中安装lombok插件可以去除编译错误，跟安装普通插件一样，File->Settings->Plugins,如下图
重启后编译错误消失，注意点击图中右下角的Enable按钮
lombok常用的注解
@Getter/@Setter
注解在类上，为所有非静态变量生产get和set方法
@ToString
注解在pojo类上面，为类生成toString方法，如果要在toString中排除一个变量，可以在该变量上面加上注解ToString.exclude,如果要在toString中打印出非静态变量，在非静态变量上增加@ToString.Include，如果要改变打印出的变量名称，在变量上加注解@ToString.Include(name = "username")，也可以通过@ToString.Include(rank = -1)来配置打印顺序，rank值越大越先打印 ·
如下示例：
@Setter
@ToString
public class ToStringExample {
private static final int STATIC_VAR = 10;
/**姓名**/
private String name;
private Square square = new Square(5, 10);
private String[] tags;
@ToString.Include(rank = 1)
private static String password = "123456";
@ToString.Exclude
private int id;
public String getName() {
return this.name;
}
@ToString(callSuper=true)
public static class Square {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
}
public static void main(String[] args){
ToStringExample toStringExample = new ToStringExample();
toStringExample.setName("jinjunzhu");
toStringExample.setTags(new String[]{"123", "234"});
System.out.println(toStringExample.toString());
}
}
打印结果如下：
ToStringExample(password=123456, name=jinjunzhu, square=ToStringExample.Square(super=boot.lombok.ToStringExample$Square@446cdf90, width=5, height=10), tags=[123, 234])
@NonNull
检查借据是否为空，如果为空，抛出空指针异常
如下代码：
public class NonNullExample {
private String name;
public NonNullExample(@NonNull String name) {
this.name = name;
}
public static void main(String[] args){
NonNullExample nonNullExample = new NonNullExample(null);
}
}
执行后结果如下：
Exception in thread "main" java.lang.NullPointerException: name is marked non-null but is null at boot.lombok.NonNullExample.<init>(NonNullExample.java:10) at boot.lombok.NonNullExample.main(NonNullExample.java:15)
@EqualsAndHashCode
为类生成equals(Object other)和hashcode()方法,默认为non-static, non-transient生成，也可以用@EqualsAndHashCode.Include或@EqualsAndHashCode.Exclude来生成或不生成
如下2段代码等价
@EqualsAndHashCode
public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
@EqualsAndHashCode.Exclude private Square shape = new Square(5, 10);
private String[] tags;
@EqualsAndHashCode.Exclude private int id;
public String getName() {
return this.name;
}
@EqualsAndHashCode()
public static class Square {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
}
}
这段代码等价于如下代码
public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
private Shape shape = new Square(5, 10);
private String[] tags;
private int id;
public String getName() {
return this.name;
}
@Override public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof EqualsAndHashCodeExample)) return false;
EqualsAndHashCodeExample other = (EqualsAndHashCodeExample) o;
if (!other.canEqual((Object)this)) return false;
if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
if (Double.compare(this.score, other.score) != 0) return false;
if (!Arrays.deepEquals(this.tags, other.tags)) return false;
return true;
}
@Override public int hashCode() {
final int PRIME = 59;
int result = 1;
final long temp1 = Double.doubleToLongBits(this.score);
result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());
result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
result = (result*PRIME) + Arrays.deepHashCode(this.tags);
return result;
}
protected boolean canEqual(Object other) {
return other instanceof EqualsAndHashCodeExample;
}
public static class Square {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
@Override public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof Square)) return false;
Square other = (Square) o;
if (!other.canEqual((Object)this)) return false;
if (!super.equals(o)) return false;
if (this.width != other.width) return false;
if (this.height != other.height) return false;
return true;
}
@Override public int hashCode() {
final int PRIME = 59;
int result = 1;
result = (result*PRIME) + super.hashCode();
result = (result*PRIME) + this.width;
result = (result*PRIME) + this.height;
return result;
}
protected boolean canEqual(Object other) {
return other instanceof Square;
}
}
}
@NoArgsConstructor/@RequiredArgsConstructor/@AllArgsConstructor
@NoArgsConstructor产生一个无参构造函数，@RequiredArgsConstructor将为没有给变量生产一个只有一个参数的构造函数，@AllArgsConstructor将生成一个有所有变量的构造函数，其中的staticName属性指定生产一个静态构造函数的名称，代码如下：
@RequiredArgsConstructor(staticName = "of")
@AllArgsConstructor(access = AccessLevel.PROTECTED)
public class ConstructorExample<T> {
private int x, y;
@NonNull
private T description;
@NoArgsConstructor
public static class NoArgsExample {
@NonNull private String field;
}
public static void main(String[] args){
ConstructorExample<User> constructorExample1 = new ConstructorExample<User>(1, 1, new User());
ConstructorExample<User> constructorExample2 = ConstructorExample.of(new User());
}
}
@Data
是 @ToString, @EqualsAndHashCode, @Getter on all fields, @Setter在所有非final变量和@RequiredArgsConstructor的汇集功能，也就是说能为POJO类所有变量生成getters方法, 为所有非final方法生产setters, toString, equals和hashCode方法代码如下：
@Data
public class DataExample {
private final String name;
@Setter(AccessLevel.PACKAGE) private int age;
private double score;
private String[] tags;
@ToString(includeFieldNames=true)
@Data(staticConstructor="of")
public static class Exercise<T> {
private final String name;
private final T value;
}
}
@Cleanup 用于代码执行完成后自动释放资源，代码如下：
public class CleanupExample {
public static void main(String[] args) throws IOException {
@Cleanup InputStream in = new FileInputStream(args[0]);
@Cleanup OutputStream out = new FileOutputStream(args[1]);
byte[] b = new byte[10000];
while (true) {
int r = in.read(b);
if (r == -1) break;
out.write(b, 0, r);
}
}
}
@Builder
引入一个复杂的构造函数，代码如下：
@Builder
public class BuilderExample {
@Builder.Default
private long created = System.currentTimeMillis();
private String name;
private int age;
@Singular
private Set<String> occupations;
public static void main(String args){
BuilderExample.builder().created(System.currentTimeMillis()).age(30).name("jinjunzhu");
}
}
还有一些不常用的变量，不一一介绍了，大家参考如下链接：
https://projectlombok.org/features/all
文中源码地址：
https://github.com/jinjunzhu/spring-boot-mybatis.git
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