# Lombok 应用指南

<!-- TOC depthFrom:2 depthTo:3 -->

- [1. Lombok 简介](#1-lombok-简介)
- [2. Lombok 安装](#2-lombok-安装)
- [3. Lombok 使用](#3-lombok-使用)
  - [3.1. @Getter and @Setter](#31-getter-and-setter)
  - [3.2. @NonNull](#32-nonnull)
  - [3.3. @ToString](#33-tostring)
  - [3.4. @EqualsAndHashCode](#34-equalsandhashcode)
  - [3.5. @Data](#35-data)
  - [3.6. @Cleanup](#36-cleanup)
  - [3.7. @Synchronized](#37-synchronized)
  - [3.8. @SneakyThrows](#38-sneakythrows)
  - [3.9. 示例源码](#39-示例源码)
- [4. 参考资料](#4-参考资料)

<!-- /TOC -->

## 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**

```xml
<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](http://jnb.ociweb.com/jnb/jnbJan2010.html#gettersetter) Lombok 代码：

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

等价于 Java 源码：

```java
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](http://jnb.ociweb.com/jnb/jnbJan2010.html#nonnull) Lombok 代码：

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

等价于 Java 源码：

```java
@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](http://jnb.ociweb.com/jnb/jnbJan2010.html#tostring) Lombok 代码：

```java
@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：

```java
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](http://jnb.ociweb.com/jnb/jnbJan2010.html#equals) Lombok 代码：

```java
@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：

```java
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](http://jnb.ociweb.com/jnb/jnbJan2010.html#data) Lombok 代码：

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

等价于 Java 源码：

```java
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](http://jnb.ociweb.com/jnb/jnbJan2010.html#cleanup) Lombok 代码：

```java
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：

```java
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](http://jnb.ociweb.com/jnb/jnbJan2010.html#synchronized) Lombok 代码：

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

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

等价于 Java 源码：

```java
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](http://jnb.ociweb.com/jnb/jnbJan2010.html#sneaky) Lombok 代码：

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

等价于 Java 源码：

```java
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](https://github.com/dunwu/java-tutorial/tree/master/javalib-bean)

## 4. 参考资料

- [Lombok 官网](https://projectlombok.org/)
- [Lombok Github](https://github.com/rzwitserloot/lombok)
- [IntelliJ IDEA - Lombok Plugin](http://plugins.jetbrains.com/plugin/6317-lombok-plugin)