Lombok的使用

1. Lombok项目是一个Java库

   Lombok是一种Java实用工具，可用来帮助开发人员消除Java中的冗长代码，尤其是对于简单的Java对象(POJO)，它通过注解实现这一目的。JSR269，其在编译阶段生效

2. Lombok的安装

1. JDK环境

拷贝jar到类路径
javac-cp lombok.jar.....

2. IDEA 下找到 plugin

导入依赖

 <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.12</version>
        <scope>provided</scope>
    </dependency>

3.常用注解

1. @Getter/@Setter

1. 插入形式

适用位置: 类（全局）字段

@Setter  //全局  
public class User {
    private  Integer uid;
    private  String username;
}

2. 可以指定生成set/get方法的权限

如指定为set方法为protect权限

3. @Getter/@Setter只对类成员产生效果，对静态变量没有任何影响，常量只有get方法生成

@Getter
@Setter(AccessLevel.PROTECTED)
public class User {
    private  Integer uid;
    private  String username;
    static String motherland="中国";
    final Double P=3.14;
}

生成代码

public class User {
    private Integer uid;
    private String username;
    static String motherland = "中国";
    final Double P = 3.14D;

    public User() {
    }

    public Integer getUid() {
        return this.uid;
    }

    public String getUsername() {
        return this.username;
    }

    public Double getP() {
        return this.P;
    }

    protected void setUid(Integer uid) {
        this.uid = uid;
    }

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

4. 排除某个字段不让其生成get方法，这个单独在某个字段设置权限，局部优先原则

@Getter
@Setter(AccessLevel.PROTECTED)
public class User {
    private  Integer uid;
    @Getter(AccessLevel.NONE)
    private  String username;
    static String motherland="中国";
    final Double P=3.14;
}

2. @ToString

适用场景: 类

1. 现象：static修改变量不会出现在toString

2. 排除某个字段，不想让其出现在toString里面---- exclude

3. 指定出现的字段---- of

3. @EqualsAndHashCode

生成的方法：equals、canEqual、hashCode常常用做对象的比较
exclude 和of 同样适用

@EqualsAndHashCode(of={"uid","username"})
public class User {
    private  Integer uid;
    private  String username;
    static String motherland="中国";
    final Double P=3.14D;
}

生成代码：

public class User {
    private Integer uid;
    private String username;
    static String motherland = "中国";
    final Double P = 3.14D;

    public User() {
    }

    public boolean equals(Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof User)) {
            return false;
        } else {
            User other = (User)o;
            if (!other.canEqual(this)) {
                return false;
            } else {
                Object this$uid = this.uid;
                Object other$uid = other.uid;
                if (this$uid == null) {
                    if (other$uid != null) {
                        return false;
                    }
                } else if (!this$uid.equals(other$uid)) {
                    return false;
                }

                Object this$username = this.username;
                Object other$username = other.username;
                if (this$username == null) {
                    if (other$username != null) {
                        return false;
                    }
                } else if (!this$username.equals(other$username)) {
                    return false;
                }

                return true;
            }
        }
    }

    protected boolean canEqual(Object other) {
        return other instanceof User;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $uid = this.uid;
        int result = result * 59 + ($uid == null ? 43 : $uid.hashCode());
        Object $username = this.username;
        result = result * 59 + ($username == null ? 43 : $username.hashCode());
        return result;
    }
}

4. @NonNull

出现位置：构造参数、方法参数，属性字段上

1. 构造参数上

2. 方法参数

3. 属性字段上

5. @NoArgsConstructor，@AllArgsConstructor，@RequiredArgsConstructor

1. @NoArgsConstructor 无参构造和@AllArgsConstructor 所有成员变量构造

2. @RequiredArgsConstructor 指定参数构造

条件：
1.指定为 @NonNull
2.表示为final.没有赋初始值的

6. @Data

囊括：
@Getter/@Setter、@RequiredArgsConstructor、@ToString、@EqualsAndHashCode

7. @Builder

流式编程、函数式编程、链式编程

生成的方法

public class User {
    private Integer uid;
    private String username;
    static String motherland = "中国";
    final Double P;

    User(Integer uid, String username, Double P) {
        this.uid = uid;
        this.username = username;
        this.P = P;
    }

    public static User.UserBuilder builder() {
        return new User.UserBuilder();
    }

    public static class UserBuilder {
        private Integer uid;
        private String username;
        private Double P;

        UserBuilder() {
        }

        public User.UserBuilder uid(Integer uid) {
            this.uid = uid;
            return this;
        }

        public User.UserBuilder username(String username) {
            this.username = username;
            return this;
        }

        public User.UserBuilder P(Double P) {
            this.P = P;
            return this;
        }

        public User build() {
            return new User(this.uid, this.username, this.P);
        }

        public String toString() {
            return "User.UserBuilder(uid=" + this.uid + ", username=" + this.username + ", P=" + this.P + ")";
        }
    }
}

测试：

public class Test {
    public static void main(String[] args) {
        System.out.println(User.builder().uid(1).username("王振强"));
    }
}

8. @Log

9. 关键字类型 val 类型推断

10. @Cleanup

使用完之后帮我进行处理
关闭连接资源
关闭文件流

public static void main(String[] args) throws IOException {
        @Cleanup FileInputStream fis=new FileInputStream("1.txt");
        @Cleanup FileOutputStream fos=new FileOutputStream("2.txt");
        byte[] b=new byte[1024];
        while(true){
            int r=0;
            if((r=fis.read(b))!=-1){
                fos.write(b,0,r);
            }
        }
    }