Lombok入门

通过使用Lombok来略去编写私有成员变量的get和set方法。减少了大量的代码冗余。、

使用Maven导入

1
2
3
4
5
6
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.22</version>
    <scope>compile</scope>
</dependency>

原理解析

Lombok是一种插件化注解API，是通过添加注解来实现的，然后在javac进行编译的时候，进行处理。

源代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
@Data
public class User {
    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    private Integer id;

    private String username;

    private String password;
}

编译后的由字节码反编译的代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
public class User {
    private Integer id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public Integer getId() {
        return this.id;
    }

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

    public String getPassword() {
        return this.password;
    }

    public void setId(Integer id) {
        this.id = id;
    }

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

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

    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 {
                label47: {
                    Object this$id = this.getId();
                    Object other$id = other.getId();
                    if (this$id == null) {
                        if (other$id == null) {
                            break label47;
                        }
                    } else if (this$id.equals(other$id)) {
                        break label47;
                    }

                    return false;
                }

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

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

                return true;
            }
        }
    }

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

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

    public String toString() {
        Integer var10000 = this.getId();
        return "User(id=" + var10000 + ", username=" + this.getUsername() + ", password=" + this.getPassword() + ")";
    }
}

我们可以看到，Lombok在编译的时候帮助我们添加了很多有用的方法，如get，set，equals，tostring等。

具体标签

@Setter 和 @Getter

可以将这两个标签添加在类前，表示给这个类的所有非静态成员变量添加（set / get）方法。

同时，声明为final的成员变量，Lombok不会为它生成Setter方法。

源代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
@Setter
public class User {
    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    private Integer id;

    private String username;

    private String password;
}

编译后的由字节码反编译的代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
public class User {
    private Integer id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public void setId(Integer id) {
        this.id = id;
    }

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

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

同时可以在标签后添加权限控制，例如：

源代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
@Setter(AccessLevel.PUBLIC)
@Getter(AccessLevel.PROTECTED)
public class User {
    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    private Integer id;

    private String username;

    private String password;
}

编译后的由字节码反编译的代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
public class User {
    private Integer id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public void setId(Integer id) {
        this.id = id;
    }

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

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

    protected Integer getId() {
        return this.id;
    }

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

    protected String getPassword() {
        return this.password;
    }
}

可以看到，经过我们的设置，所有的get方法的访问权限都为protected，所有的set方法的访问权限都为public。

同时，该标签还可以添加在成员变量之前：

源代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
public class User {
    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }
    @Getter
    private Integer id;

    @Getter
    @Setter
    private String username;

    @Getter
    private String password;
}

编译后的由字节码反编译的代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
public class User {
    private Integer id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public Integer getId() {
        return this.id;
    }

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

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

    public String getPassword() {
        return this.password;
    }
}

如果在静态成员变量前添加标签，生成的getter和setter方法都将是静态的。

@Accessors

通过Accessors标签来设置@Getter和@Setter的样式。

@Accessors(chain = true)

该类的Setter方法会返回this（即该类的实例），所以我们就可以链式调用这些方法，例如：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
public User setId(Integer id) {
    this.id = id;
    return this;
}

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

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

在使用时，可以这样：

1
2
3
4
public void Usertry() {
    User user = new User();
    user.setUsername("abaaba").setPassword("123").setId(1);
}

@Accessors(fluent = true)

会通过多态，直接将Setter和Getter的方法名全设置为成员变量的名字。

源码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
@Accessors(fluent = true)
@Getter
@Setter
public class User {
    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public User() {};

    private Integer id;

    private String username;

    private String password;
}

编译后的由字节码反编译的代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
public class User {
    private Integer id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public User() {
    }

    public Integer id() {
        return this.id;
    }

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

    public String password() {
        return this.password;
    }

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

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

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

@ToString

为该类实现一个toString方法。

源码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
@ToString
public class User {
    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public User() {};

    private Integer id;

    private String username;

    private String password;
}

编译后的由字节码反编译的代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
public class User {
    private Integer id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.password = password;
        this.username = username;
    }

    public User() {
    }

    public String toString() {
        return "User(id=" + this.id + ", username=" + this.username + ", password=" + this.password + ")";
    }
}

还可以通过添加不同参数来限制toString的功能。

includeFieldNames

1
2
@ToString(includeFieldNames = false)
public class User {
1
2
3
public String toString() {
    return "User(" + this.id + ", " + this.username + ", " + this.password + ")";
}

默认为True，False状态下tostring隐藏成员变量的类型。

exclude

1
2
@ToString(exclude = {"id"})
public class User {
1
2
3
public String toString() {
    return "User(username=" + this.username + ", password=" + this.password + ")";
}

在exclude中添加想要省略的成员变量的名称（字符串），toString函数会省略这些成员变量的转化。

of

1
2
@ToString(of = {"id"})
public class User {
1
2
3
public String toString() {
    return "User(id=" + this.id + ")";
}

在of中添加想要显示的成员变量的名称（字符串），toString函数只会完成这些成员变量的转化。（与exclude相反）

callSuper

1
2
@ToString(callSuper = true)
public class User {	
1
2
3
4
public String toString() {
    String var10000 = super.toString();
    return "User(super=" + var10000 + ", id=" + this.id + ", username=" + this.username + ", password=" + this.password + ")";
}

默认为false，改为true后会调用父类的toString()方法。

doNotUseGetters

如果成员变量存在getter方法，在tostring时会默认调用getter方法来获取成员变量。将该值设为true后将直接获取成员变量的值。

onlyExplicitlyIncluded

1
2
@ToString(onlyExplicitlyIncluded = true)
public class User {

默认为false，设为true后将只会显示类名

1
2
3
public String toString() {
    return "User()";
}

Include

rank

通过添加rank来规定转化后字符串中变量的顺序。（rank值越大优先级越高）

1
2
3
4
5
6
7
8
@ToString.Include(rank = 1)
private Integer id;

@ToString.Include(rank = 0)
private String username;

@ToString.Include(rank = 2)
private String password;
1
2
3
public String toString() {
    return "User(password=" + this.password + ", id=" + this.id + ", username=" + this.username + ")";
}
name

设置别名，添加后转化后的字符串中变量的类型将会被别名替换掉

1
2
@ToString.Include(name = "学号")
private Integer id;
1
2
3
public String toString() {
    return "User(password=" + this.password + ", 学号=" + this.id + ", username=" + this.username + ")";
}

@EqualsAndHashCode

该标签只允许添加在类前。

重写Equals方法，使得类在比较的过程中对成员变量进行一一的确认，以此来比较是否相等。

该标签也包括exclude和of方法，具体功能和@TosString类似。

@AllArgsConstructor

1
2
@AllArgsConstructor
public class User {
1
2
3
4
5
public User(Integer id, String username, String password) {
    this.id = id;
    this.username = username;
    this.password = password;
}

该标签只能添加在类前，默认为类生成全参数构造。

注意：添加该标签后会使得默认的无参构造方法失效。

该标签也可添加access注解来限制构造方法的访问控制。

1
2
@AllArgsConstructor(access = AccessLevel.PUBLIC)
public class User {

该标签也可添加staticName注解来添加public的静态 类构造方法 ，添加后，原来的无参构造方法的可访问性将被修改成private

1
2
@AllArgsConstructor(staticName = "setUser")
public class User {
1
2
3
4
5
6
7
8
9
private User(Integer id, String username, String password) {
    this.id = id;
    this.username = username;
    this.password = password;
}

public static User setUser(Integer id, String username, String password) {
    return new User(id, username, password);
}

可以看到，自动生成了一个名为“setUser”的静态全参构造方法。

@NoArgsConstructor

生成默认的无参构造方法。

1
@NoArgsConstructor(access = AccessLevel.PUBLIC)

其余参数和@AllArgsConstructor一致。

1
2
public User() {
}

@RequiredArgsConstructor

为类中生成包含对标记为final或者@NonNull的成员变量的赋值的构造方法。

1
2
3
4
5
6
@RequiredArgsConstructor
public class User {
    @NonNull
    private Integer id;
    
    final private String username;
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
public class User {
    @NonNull
    private Integer id;
    private final String username;
    private String password;

    public User(@NonNull Integer id, String username) {
        if (id == null) {
            throw new NullPointerException("id is marked non-null but is null");
        } else {
            this.id = id;
            this.username = username;
        }
    }
}

其余参数和@AllArgsConstructor一致。

@Data

该标签只能添加在类前。

等价于在类前同时添加了@Setter、@Getter、@RequiredArgsConstructor、@ToString、@EqualsAndHashCode。

添加@Data标签后不推荐对该类进行继承，可能会导致Equals方法异常。

@Value

具体功能和@Data类似。

但是！生成的所有成员变量的属性都是private final的（这意味着没有setter方法）。

@SneakyThrows

该标签只能添加在方法前，表示为该方法添加了try / catch。

1
2
@SneakyThrows(IOException.class)
public void abaaba() {

可以在注解之后添加异常的类来规定抛出的具体异常。

@Cleanup

为该变量自动添加close()方法。

@Builder

1
2
@Builder
public class User {
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
public class User {
    private Integer id;
    private String username;
    private String password;

    User(Integer id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

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

    public static class UserBuilder {
        private Integer id;
        private String username;
        private String password;

        UserBuilder() {
        }

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

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

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

        public User build() {
            return new User(this.id, this.username, this.password);
        }

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