Android上使用Lombok

Android上使用Lombok


[TOC]

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。

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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。

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@Data
public 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

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lombok.anyConstructor.suppressConstructorProperties=true

然后在对应的项目中添加gradle依赖就行了。

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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:

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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:

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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:

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public class NonNullExample {

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

class字节码

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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

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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

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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

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// GetterSetterExample.java
public class GetterSetterExample {

@Getter
@Setter
private int age;

@Setter(AccessLevel.PROTECTED)
private String name;
}

// GetterSetterExample.class
public 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

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// 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.class
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;
}

public String toString() {
return "ToStringExample(name=" + this.name + ", passwd=" + this.passwd + ")";
}
}

@EqualsAndHashCode

自动生成equals和hashcode方法。

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// EqualsAndHashCodeExample.java
@EqualsAndHashCode
public class EqualsAndHashCodeExample {

private int id;

private String name;

public EqualsAndHashCodeExample(int id, String name) {
this.id = id;
this.name = name;
}
}

// EqualsAndHashCodeExample.class
public 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

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// 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.class
public 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

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// BuilderExample.java

@Builder
@Data
public 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。

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// test builder
BuilderExample 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

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// SneakyThrowsExample.java

public 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.class
public 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

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// SynchronizedExample.java
public 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.class
public 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

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// GetterLazyExample.java
public 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.class
public 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

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