Android上使用Lombok

---

简介

最近几天尝试了一把后端的工作，发现后端同学使用了一个第三库——Lombok，用了一下，感觉还不错，特来介绍一下，感觉和以前介绍过的AutoValue挺像的。

Lombok 官网上面有个几分钟的视频，接单介绍了Lombok的用途，使用方法很简单，只需要依赖对应的jar文件，然后在对应的Java文件上使用注解即可。

先看个例子，下面是常见的一个Java一个实体类，含有field、setter、getter、equals、hashcode、toString方法。

public class User {    private int id;    private String name;    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    @Override    public boolean equals(Object o) {        if (this == o) return true;        if (o == null || getClass() != o.getClass()) return false;        User user = (User) o;        if (id != user.id) return false;        return name != null ? name.equals(user.name) : user.name == null;    }    @Override    public int hashCode() {        int result = id;        result = 31 * result + (name != null ? name.hashCode() : 0);        return result;    }    @Override    public String toString() {        return "User{" +                "id=" + id +                ", name='" + name + '\'' +                '}';    }}

如果使用了Lombok，就很简单了，直接定义好字段，然后添加一个注解@Data即可，其他方法，工具自动生成，虽然上面的方法我们也是用工具生成的，但是如果要添加或者删除字段，还是要修改代码的，如果直接使用注解的方式，那么还是简单的，无需修改任何方法。

@Datapublic class UserLombok {    private int id;    private String name;}

注解简介

Lombok 主要使用就是通过添加注解，来自动生成代码，主要包含两类，一种是Stable类型，一种是Experimental。前面表示稳定的注解，后面表示实验类型的，可能会被移除。本文主要介绍Stable类型，Experimental由于使用较少，不做讲解。

Stable

• val

Finally! Hassle-free final local variables.

• @NonNull

or: How I learned to stop worrying and love the NullPointerException.

• @Cleanup

Automatic resource management: Call your close() methods safely with no hassle.

• @Getter/@Setter

Never write public int getFoo() {return foo;} again.

• @ToString

No need to start a debugger to see your fields: Just let lombok generate a toString for you!

• @EqualsAndHashCode

Equality made easy: Generates hashCode and equals implementations from the fields of your object..

• @NoArgsConstructor, @RequiredArgsConstructor and @AllArgsConstructor

Constructors made to order: Generates constructors that take no arguments, one argument per final / non-nullfield, or one argument for every field.

• @Data

All together now: A shortcut for @ToString, @EqualsAndHashCode, @Getter on all fields, and @Setter on all non-final fields, and @RequiredArgsConstructor!

• @Value

Immutable classes made very easy.

• @Builder

… and Bob’s your uncle: No-hassle fancy-pants APIs for object creation!

• @SneakyThrows

To boldly throw checked exceptions where no one has thrown them before!

• @Synchronized

synchronized done right: Don’t expose your locks.

• @Getter(lazy=true)

Laziness is a virtue!

• @Log

Captain’s Log, stardate 24435.7: “What was that line again?”

Experimental

• var

Modifiable local variables with a type inferred by assigning value.

• @Accessors

A more fluent API for getters and setters.

• @ExtensionMethod

Annoying API? Fix it yourself: Add new methods to existing types!

• @FieldDefaults

New default field modifiers for the 21st century.

• @Delegate

Don’t lose your composition.

• @Wither

Immutable ‘setters’ - methods that create a clone but with one changed field.

• onMethod= / onConstructor= / onParam=

Sup dawg, we heard you like annotations, so we put annotations in your annotations so you can annotate while you’re annotating.

• @UtilityClass

Utility, metility, wetility! Utility classes for the masses.

• @Helper

With a little help from my friends… Helper methods for java.

Android 集成

项目根目录下面新建配置文件 lombok.config，同时填上对应的配置项，Java项目不需要，Android和Java还是有点区别的，不配置有的注解使用不了，编译不过。

lombok.config

lombok.anyConstructor.suppressConstructorProperties=true

然后在对应的项目中添加gradle依赖就行了。

dependencies {    provided "org.projectlombok:lombok:1.16.18"    compile 'org.glassfish:javax.annotation:10.0-b28'}

可以在Android Studio中安装lombok插件。

这样可以很方便的看到类中生成的方法

注解说明

下面简单说明注解的使用方法（如需了解详细使用，请参阅官方文档），以及使用注解后类中生成的方法。

val

定义一个final类型的变量，并且可以不写类型。

如:

public class ValExample {    public String example() {        val example = new ArrayList<String>();        example.add("Hello, World!");        val foo = example.get(0);        return foo.toLowerCase();    }    public void example2() {        val map = new HashMap<Integer, String>();        map.put(0, "zero");        map.put(5, "five");        for (val entry : map.entrySet()) {            System.out.printf("%d: %s\n", entry.getKey(), entry.getValue());        }    }}

class字节码：

public class ValExample {    public ValExample() {    }    public String example() {        ArrayList<String> example = new ArrayList();        example.add("Hello, World!");        String foo = (String)example.get(0);        return foo.toLowerCase();    }    public void example2() {        HashMap<Integer, String> map = new HashMap();        map.put(Integer.valueOf(0), "zero");        map.put(Integer.valueOf(5), "five");        Iterator var2 = map.entrySet().iterator();        while(var2.hasNext()) {            Entry<Integer, String> entry = (Entry)var2.next();            System.out.printf("%d: %s\n", new Object[]{entry.getKey(), entry.getValue()});        }    }}

@NonNull

非空值判断，如果为空，则抛出异常

如：

public class NonNullExample {    public static int length(@NonNull String string) {        return string.length();    }}

class字节码

public class NonNullExample {    public NonNullExample() {    }    public static int length(@NonNull String string) {        if(string == null) {            throw new NullPointerException("string");        } else {            return string.length();        }    }}

@Cleanup

可以自动调用close方法

如

public class CleanupExample {    public static void main(String[] args) throws IOException {        @Cleanup InputStream in = new FileInputStream(args[0]);        @Cleanup OutputStream out = new FileOutputStream(args[1]);        byte[] b = new byte[10000];        while (true) {            int r = in.read(b);            if (r == -1) break;            out.write(b, 0, r);        }    }}

class字节码

public class CleanupExample {    public CleanupExample() {    }    public static void main(String[] args) throws IOException {        FileInputStream in = new FileInputStream(args[0]);        try {            FileOutputStream out = new FileOutputStream(args[1]);            try {                byte[] b = new byte[10000];                while(true) {                    int r = in.read(b);                    if(r == -1) {                        return;                    }                    out.write(b, 0, r);                }            } finally {                if(Collections.singletonList(out).get(0) != null) {                    out.close();                }            }        } finally {            if(Collections.singletonList(in).get(0) != null) {                in.close();            }        }    }}

@Getter/@Setter

自动生成setter、getter方法

// GetterSetterExample.javapublic class GetterSetterExample {    @Getter    @Setter    private int age;    @Setter(AccessLevel.PROTECTED)    private String name;}// GetterSetterExample.classpublic class GetterSetterExample {    private int age;    private String name;    public GetterSetterExample() {    }    public int getAge() {        return this.age;    }    public void setAge(int age) {        this.age = age;    }    protected void setName(String name) {        this.name = name;    }}

@ToString

自动生成toString方法

// ToStringExample.java@ToString(exclude = "id")public class ToStringExample {    private int id;    private String name;    private String passwd;    public ToStringExample(int id, String name, String passwd) {        this.id = id;        this.name = name;        this.passwd = passwd;    }}// ToStringExample.classpublic class ToStringExample {    private int id;    private String name;    private String passwd;    public ToStringExample(int id, String name, String passwd) {        this.id = id;        this.name = name;        this.passwd = passwd;    }    public String toString() {        return "ToStringExample(name=" + this.name + ", passwd=" + this.passwd + ")";    }}

@EqualsAndHashCode

自动生成equals和hashcode方法。

// EqualsAndHashCodeExample.java@EqualsAndHashCodepublic class EqualsAndHashCodeExample {    private int id;    private String name;    public EqualsAndHashCodeExample(int id, String name) {        this.id = id;        this.name = name;    }}// EqualsAndHashCodeExample.classpublic class EqualsAndHashCodeExample {    private int id;    private String name;    public EqualsAndHashCodeExample(int id, String name) {        this.id = id;        this.name = name;    }    public boolean equals(Object o) {        if(o == this) {            return true;        } else if(!(o instanceof EqualsAndHashCodeExample)) {            return false;        } else {            EqualsAndHashCodeExample other = (EqualsAndHashCodeExample)o;            if(!other.canEqual(this)) {                return false;            } else if(this.id != other.id) {                return false;            } else {                Object this$name = this.name;                Object other$name = other.name;                if(this$name == null) {                    if(other$name != null) {                        return false;                    }                } else if(!this$name.equals(other$name)) {                    return false;                }                return true;            }        }    }    protected boolean canEqual(Object other) {        return other instanceof EqualsAndHashCodeExample;    }    public int hashCode() {        int PRIME = true;        int result = 1;        int result = result * 59 + this.id;        Object $name = this.name;        result = result * 59 + ($name == null?43:$name.hashCode());        return result;    }}

@NoArgsConstructor, @RequiredArgsConstructor and @AllArgsConstructor

自动生成相关的构造函数

// ConstructorExample.java@ToString@NoArgsConstructor@AllArgsConstructor(access = AccessLevel.PUBLIC)public class ConstructorExample<T> {    private String args;    @ToString    @RequiredArgsConstructor(staticName = "of")    public static class StaticMethodsExample {        @NonNull        private String field;    }}// ConstructorExample.classpublic class ConstructorExample<T> {    private String args;    public String toString() {        return "ConstructorExample(args=" + this.args + ")";    }    public ConstructorExample() {    }    public ConstructorExample(String args) {        this.args = args;    }    public static class StaticMethodsExample {        @NonNull        private String field;        public String toString() {            return "ConstructorExample.StaticMethodsExample(field=" + this.field + ")";        }        private StaticMethodsExample(@NonNull String field) {            if(field == null) {                throw new NullPointerException("field");            } else {                this.field = field;            }        }        public static ConstructorExample.StaticMethodsExample of(@NonNull String field) {            return new ConstructorExample.StaticMethodsExample(field);        }    }}

@Builder

自动生成构造者模式方法

// BuilderExample.java@Builder@Datapublic class BuilderExample {    private String name;    private int age;    @Singular    private Set<String> occupations;}

class文件太长，就不贴了，下面是调用方式。

// test builderBuilderExample builderExample = BuilderExample.builder()    .name("admin")    .age(10)    .occupation("aaa")    .occupation("bbb")    .build();Log.i(TAG, "onCreate: " + builderExample);

@SneakyThrows

自动生成异常抛出代码

// SneakyThrowsExample.javapublic class SneakyThrowsExample implements Runnable {    @SneakyThrows(UnsupportedEncodingException.class)    public String utf8ToString(byte[] bytes) {        return new String(bytes, "UTF-8");    }    @SneakyThrows    public void run() {        throw new Throwable();    }}// SneakyThrowsExample.classpublic class SneakyThrowsExample implements Runnable {    public SneakyThrowsExample() {    }    public String utf8ToString(byte[] bytes) {        try {            return new String(bytes, "UTF-8");        } catch (UnsupportedEncodingException var3) {            throw var3;        }    }    public void run() {        try {            throw new Throwable();        } catch (Throwable var2) {            throw var2;        }    }}

@Synchronized

自动生成线程同步代码

// SynchronizedExample.javapublic class SynchronizedExample {    private final Object readLock = new Object();    @Synchronized    public static void hello() {        System.out.println("world");    }    @Synchronized    public int answerToLife() {        return 42;    }    @Synchronized("readLock")    public void foo() {        System.out.println("bar");    }}// SynchronizedExample.classpublic class SynchronizedExample {    private static final Object $LOCK = new Object[0];    private final Object $lock = new Object[0];    private final Object readLock = new Object();    public SynchronizedExample() {    }    public static void hello() {        Object var0 = $LOCK;        synchronized($LOCK) {            System.out.println("world");        }    }    public int answerToLife() {        Object var1 = this.$lock;        synchronized(this.$lock) {            return 42;        }    }    public void foo() {        Object var1 = this.readLock;        synchronized(this.readLock) {            System.out.println("bar");        }    }}

@Getter(lazy=true)

延迟初始化

// GetterLazyExample.javapublic class GetterLazyExample {    @Getter(lazy = true)    private final double[] cached = expensive();    private double[] expensive() {        double[] result = new double[1000000];        for (int i = 0; i < result.length; i++) {            result[i] = Math.asin(i);        }        return result;    }}// GetterLazyExample.classpublic class GetterLazyExample {    private final AtomicReference<Object> cached = new AtomicReference();    public GetterLazyExample() {    }    private double[] expensive() {        double[] result = new double[1000000];        for(int i = 0; i < result.length; ++i) {            result[i] = Math.asin((double)i);        }        return result;    }    public double[] getCached() {        Object value = this.cached.get();        if(value == null) {            AtomicReference var2 = this.cached;            synchronized(this.cached) {                value = this.cached.get();                if(value == null) {                    double[] actualValue = this.expensive();                    value = actualValue == null?this.cached:actualValue;                    this.cached.set(value);                }            }        }        return (double[])((double[])(value == this.cached?null:value));    }}

@Log

自动生成日志对象，不过都是J2EE方面的，Android端用途不大。

官方示例

原理

自从Java 6起，javac就支持“JSR 269 Pluggable Annotation Processing API”规范，只要程序实现了该API，就能在javac运行的时候得到调用。

举例来说，现在有一个实现了”JSR 269 API”的程序A,那么使用javac编译源码的时候具体流程如下：

1. javac对源代码进行分析，生成一棵抽象语法树(AST)

2. 运行过程中调用实现了”JSR 269 API”的A程序

3. 此时A程序就可以完成它自己的逻辑，包括修改第一步骤得到的抽象语法树(AST)

4. javac使用修改后的抽象语法树(AST)生成字节码文件

详细的流程图如下：

总结

综上所述，使用了lombok可以简化Java代码，因为是在编译期处理所以可能会增加点时间，不过对于Android来说，可以尝试一下，不过17年Google IO已经推荐使用Kotlin开发Android了，lombok中好多功能在Kotlin中已经实现了，如果项目暂时还不想使用Kotlin开发，继续使用Java的可以尝试一下。

缺点：

使用lombok虽然能够省去手动创建代码的麻烦，但是却大大降低了源代码文件的可读性和完整性，降低了阅读源代码的舒适度。

相关链接

Lombok官网

AutoValue相关

android基础之依赖注入问题

Lombok的使用和原理