参考
https://projectlombok.org/features/
添加依赖
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
@Getter和@Setter
自动生成Getter和Setter方法
import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;
public class User {
@Getter @Setter private Integer id;
@Setter(AccessLevel.PROTECTED) private String name;
}
等效的java代码
public class User {
private Integer id;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
protected void setName(String name) {
this.name = name;
}
}
@ToString
自动生成toString()方法
import lombok.ToString;
@ToString
public class User {
private Integer id = 1;
private String name = "zhangsan";
private String password = "xxx";
public static void main(String[] args) {
User user = new User();
System.out.println(user);
}
}
执行结果
User(id=1, name=zhangsan, password=xxx)
等效的toString()代码
@Override
public String toString() {
return "User{" + "id=" + id + ", name=" + name + ", password=" + password + "}";
}
idea自动生成的toString()会将String类型用单引号'括起来, 二者略有差别
@Override
public String toString() {
return "User{" + "id=" + id + ", name='" + name + '\'' + ", password='" + password + '\'' + '}';
}
对应结果为:
User{id=1, name='zhangsan', password='xxx'}
如果只想展示部分字段, 可用of来指定字段, 或者使用exclude来排除字段
@ToString(of = {"id", "name"})
或者
@ToString(exclude = {"password"})
或者直接注解字段 @ToString.Exclude
@ToString.Exclude private String password = "xxx";
对应结果为:
User(id=1, name=zhangsan)
@EqualsAndHashCode
除了生成equals()和hashCode(), 还有一个canEqual(Object other), 用来判断对象other是否是当前类的实例
官网示例: https://projectlombok.org/features/EqualsAndHashCode
构造方法
@NoArgsConstructor: 无参构造方法
@AllArgsConstructor: 全参构造方法
@RequiredArgsConstructor: 部分参数构造方法,需要搭配@NonNull使用
官网示例: https://projectlombok.org/features/constructor
@Data
一般情况下, 这一个注解就相当于上面的 @Getter @Setter @ToString @EqualsAndHashCode @NoArgsConstructor
如果有字段加了@NonNull, 则相当于 @RequiredArgsConstructor
也可以通过以下命令来验证:
#编译.java文件,生成.class文件
javac -cp .\lombok-1.18.16.jar .\User.java
#反编译.class文件,查看类的具体信息
javap User
@Cleanup
资源操作时,自动调用close()方法
import lombok.Cleanup;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class TestCleanup {
public static void main(String[] args) throws IOException {
@Cleanup InputStream is = new FileInputStream("/home/1.txt");
@Cleanup OutputStream os = new FileOutputStream("/home/2.txt");
byte[] bytes = new byte[1024];
while (true) {
int length = is.read(bytes);
if (length == -1) {
break;
}
os.write(bytes, 0, length);
}
}
}
等效的java代码
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class TestCleanup {
public static void main(String[] args) throws IOException {
InputStream is = new FileInputStream("/home/1.txt");
try {
OutputStream os = new FileOutputStream("/home/2.txt");
try {
byte[] bytes = new byte[1024];
while (true) {
int length = is.read(bytes);
if (length == -1) {
break;
}
os.write(bytes, 0, length);
}
} finally {
if (os != null) {
os.close();
}
}
} finally {
if (is != null) {
is.close();
}
}
}
}
@Builder
import lombok.Builder;
@Builder
public class User {
private Integer id;
private String name;
}
可以实现链式调用的写法,赋值方便
User user = User.builder().id(1).name("zhangsan").build();
反编译后
public class User {
private Integer id;
private String name;
User(Integer var1, String var2) {
this.id = var1;
this.name = var2;
}
public static User.UserBuilder builder() {
return new User.UserBuilder();
}
public static class UserBuilder {
private Integer id;
private String name;
UserBuilder() {
}
public User.UserBuilder id(Integer var1) {
this.id = var1;
return this;
}
public User.UserBuilder name(String var1) {
this.name = var1;
return this;
}
public User build() {
return new User(this.id, this.name);
}
public String toString() {
return "User.UserBuilder(id=" + this.id + ", name=" + this.name + ")";
}
}
}
编译后的代码中, 多了一个静态内部类 User.UserBuilder, 属性和 User 相同
- 每个属性都有一个类似
setter的方法, 但返回的是对象本身, 使得可以实现链式调用的写法 @Builder会默认生成一个全参构造方法, 如果想用无参构造方法需要把@NoArgsConstructor和@AllArgsConstructor都加上- 如果只加了
@NoArgsConstructor会覆盖全参构造方法,导致报错
优点: 链式调用写法赋值更方便, 注意如果赋值较多,不要写在一行,不利于阅读维护
缺点: 生成User示例之前, 会先生成User.UserBuilder实例,额外占用内存
选项toBuilder, 默认false, 为true时, 会多一个toBuilder()方法
@Builder(toBuilder = true)
public class User {
//...
}
//编译后代码
public class User {
//...
//编译后多了一个 toBuilder()方法
//用当前对象的属性来构造一个新的Builder对象
public User.UserBuilder toBuilder() {
return (new User.UserBuilder()).id(this.id).name(this.name);
}
//...
}