Lombok 应用指南

1. Lombok 简介

Lombok 是一种 Java 实用工具，可用来帮助开发人员消除 Java 的冗长，尤其是对于简单的 Java 对象（POJO）。它通过注释实现这一目的。通过在开发环境中实现 Lombok，开发人员可以节省构建诸如 hashCode() 和 equals() 、getter / setter 这样的方法以及以往用来分类各种 accessor 和 mutator 的大量时间。

2. Lombok 安装

使 IntelliJ IDEA 支持 Lombok 方式如下：

  • Intellij 设置支持注解处理

    • 点击 File > Settings > Build > Annotation Processors

    • 勾选 Enable annotation processing

  • 安装插件

    • 点击 Settings > Plugins > Browse repositories

    • 查找 Lombok Plugin 并进行安装

    • 重启 IntelliJ IDEA

  • 将 lombok 添加到 pom 文件

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.16.8</version>
</dependency>

3. Lombok 使用

Lombok 提供注解 API 来修饰指定的类：

3.1. @Getter and @Setter

@Getter and @Setter Lombok 代码：

@Getter @Setter private boolean employed = true;
@Setter(AccessLevel.PROTECTED) private String name;

等价于 Java 源码：

private boolean employed = true;
private String name;

public boolean isEmployed() {
    return employed;
}

public void setEmployed(final boolean employed) {
    this.employed = employed;
}

protected void setName(final String name) {
    this.name = name;
}

3.2. @NonNull

@NonNull Lombok 代码：

@Getter @Setter @NonNull
private List<Person> members;

等价于 Java 源码：

@NonNull
private List<Person> members;

public Family(@NonNull final List<Person> members) {
    if (members == null) throw new java.lang.NullPointerException("members");
    this.members = members;
}

@NonNull
public List<Person> getMembers() {
    return members;
}

public void setMembers(@NonNull final List<Person> members) {
    if (members == null) throw new java.lang.NullPointerException("members");
    this.members = members;
}

3.3. @ToString

@ToString Lombok 代码：

@ToString(callSuper=true,exclude="someExcludedField")
public class Foo extends Bar {
    private boolean someBoolean = true;
    private String someStringField;
    private float someExcludedField;
}

等价于 Java 源码：

public class Foo extends Bar {
    private boolean someBoolean = true;
    private String someStringField;
    private float someExcludedField;

    @java.lang.Override
    public java.lang.String toString() {
        return "Foo(super=" + super.toString() +
            ", someBoolean=" + someBoolean +
            ", someStringField=" + someStringField + ")";
    }
}

3.4. @EqualsAndHashCode

@EqualsAndHashCode Lombok 代码：

@EqualsAndHashCode(callSuper=true,exclude={"address","city","state","zip"})
public class Person extends SentientBeing {
    enum Gender { Male, Female }

    @NonNull private String name;
    @NonNull private Gender gender;

    private String ssn;
    private String address;
    private String city;
    private String state;
    private String zip;
}

等价于 Java 源码：

public class Person extends SentientBeing {

    enum Gender {
        /*public static final*/ Male /* = new Gender() */,
        /*public static final*/ Female /* = new Gender() */;
    }
    @NonNull
    private String name;
    @NonNull
    private Gender gender;
    private String ssn;
    private String address;
    private String city;
    private String state;
    private String zip;

    @java.lang.Override
    public boolean equals(final java.lang.Object o) {
        if (o == this) return true;
        if (o == null) return false;
        if (o.getClass() != this.getClass()) return false;
        if (!super.equals(o)) return false;
        final Person other = (Person)o;
        if (this.name == null ? other.name != null : !this.name.equals(other.name)) return false;
        if (this.gender == null ? other.gender != null : !this.gender.equals(other.gender)) return false;
        if (this.ssn == null ? other.ssn != null : !this.ssn.equals(other.ssn)) return false;
        return true;
    }

    @java.lang.Override
    public int hashCode() {
        final int PRIME = 31;
        int result = 1;
        result = result * PRIME + super.hashCode();
        result = result * PRIME + (this.name == null ? 0 : this.name.hashCode());
        result = result * PRIME + (this.gender == null ? 0 : this.gender.hashCode());
        result = result * PRIME + (this.ssn == null ? 0 : this.ssn.hashCode());
        return result;
    }
}

3.5. @Data

@Data Lombok 代码：

@Data(staticConstructor="of")
public class Company {
    private final Person founder;
    private String name;
    private List<Person> employees;
}

等价于 Java 源码：

public class Company {
    private final Person founder;
    private String name;
    private List<Person> employees;

    private Company(final Person founder) {
        this.founder = founder;
    }

    public static Company of(final Person founder) {
        return new Company(founder);
    }

    public Person getFounder() {
        return founder;
    }

    public String getName() {
        return name;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public List<Person> getEmployees() {
        return employees;
    }

    public void setEmployees(final List<Person> employees) {
        this.employees = employees;
    }

    @java.lang.Override
    public boolean equals(final java.lang.Object o) {
        if (o == this) return true;
        if (o == null) return false;
        if (o.getClass() != this.getClass()) return false;
        final Company other = (Company)o;
        if (this.founder == null ? other.founder != null : !this.founder.equals(other.founder)) return false;
        if (this.name == null ? other.name != null : !this.name.equals(other.name)) return false;
        if (this.employees == null ? other.employees != null : !this.employees.equals(other.employees)) return false;
        return true;
    }

    @java.lang.Override
    public int hashCode() {
        final int PRIME = 31;
        int result = 1;
        result = result * PRIME + (this.founder == null ? 0 : this.founder.hashCode());
        result = result * PRIME + (this.name == null ? 0 : this.name.hashCode());
        result = result * PRIME + (this.employees == null ? 0 : this.employees.hashCode());
        return result;
    }

    @java.lang.Override
    public java.lang.String toString() {
        return "Company(founder=" + founder + ", name=" + name + ", employees=" + employees + ")";
    }
}

3.6. @Cleanup

@Cleanup Lombok 代码：

public void testCleanUp() {
    try {
        @Cleanup ByteArrayOutputStream baos = new ByteArrayOutputStream();
        baos.write(new byte[] {'Y','e','s'});
        System.out.println(baos.toString());
    } catch (IOException e) {
        e.printStackTrace();
    }
}

等价于 Java 源码：

public void testCleanUp() {
    try {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            baos.write(new byte[]{'Y', 'e', 's'});
            System.out.println(baos.toString());
        } finally {
            baos.close();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

3.7. @Synchronized

@Synchronized Lombok 代码：

private DateFormat format = new SimpleDateFormat("MM-dd-YYYY");

@Synchronized
public String synchronizedFormat(Date date) {
    return format.format(date);
}

等价于 Java 源码：

private final java.lang.Object $lock = new java.lang.Object[0];
private DateFormat format = new SimpleDateFormat("MM-dd-YYYY");

public String synchronizedFormat(Date date) {
    synchronized ($lock) {
        return format.format(date);
    }
}

3.8. @SneakyThrows

@SneakyThrows Lombok 代码：

@SneakyThrows
public void testSneakyThrows() {
    throw new IllegalAccessException();
}

等价于 Java 源码：

public void testSneakyThrows() {
    try {
        throw new IllegalAccessException();
    } catch (java.lang.Throwable $ex) {
        throw lombok.Lombok.sneakyThrow($ex);
    }
}

3.9. 示例源码

示例源码：javalib-bean

4. 参考资料

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