最近IDEA 2020最初一个版本公布了，曾经内置了Lombok插件，SpringBoot 2.1.x之后的版本也在Starter中内置了Lombok依赖。为什么他们都要反对Lombok呢？明天我来讲讲Lombok的应用，看看它有何神奇之处！
SpringBoot实战电商我的项目mall（40k+star）地址：https://github.com/macrozheng/mall
Lombok简介
Lombok是一款Java代码性能加强库，在Github上已有9.8k+Star。它会主动集成到你的编辑器和构建工具中，从而使你的Java代码更加生动有趣。通过Lombok的注解，你能够不必再写getter、setter、equals等办法，Lombok将在编译时为你主动生成。
Lombok集成
首先咱们须要在IDEA中装置好Lombok插件，如果你应用的是最新版IDEA 2020.3，则Lombok插件曾经内置，无需装置。
之后在我的项目的pom.xml文件中增加Lombok依赖，SpringBoot 2.1.x版本后无需指定Lombok版本，SpringBoot在spring-boot-dependencies中曾经内置。
<!--lombok依赖--><dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional></dependency>Lombok应用
Lombok中有很多注解，这些注解使得咱们能够更加不便的编写Java代码，上面介绍下这些注解的应用。
val
应用val注解能够取代任意类型作为局部变量，这样咱们就不必写简单的ArrayList和Map.Entry类型了，具体例子如下。
/** * Created by macro on 2020/12/16. */public class ValExample { public static void example() { //val代替ArrayList<String>和String类型 val example = new ArrayList<String>(); example.add("Hello World!"); val foo = example.get(0); System.out.println(foo.toLowerCase()); } public static void example2() { //val代替Map.Entry<Integer,String>类型 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()); } } public static void main(String[] args) { example(); example2(); }}当咱们应用了val注解后，Lombok会从局部变量的初始化表达式推断出具体类型，编译后会生成如下代码。
public class ValExample { public ValExample() { } public static void example() { ArrayList<String> example = new ArrayList(); example.add("Hello World!"); String foo = (String)example.get(0); System.out.println(foo.toLowerCase()); } public static void example2() { HashMap<Integer, String> map = new HashMap(); map.put(0, "zero"); map.put(5, "five"); Iterator var1 = map.entrySet().iterator(); while(var1.hasNext()) { Entry<Integer, String> entry = (Entry)var1.next(); System.out.printf("%d: %s\n", entry.getKey(), entry.getValue()); } }}@NonNull
在办法上应用@NonNull注解能够做非空判断，如果传入空值的话会间接抛出NullPointerException。
/** * Created by macro on 2020/12/16. */public class NonNullExample { private String name; public NonNullExample(@NonNull String name){ this.name = name; } public static void main(String[] args) { new NonNullExample("test"); //会抛出NullPointerException new NonNullExample(null); }}编译后会在结构器中增加非空判断，具体代码如下。
public class NonNullExample { private String name; public NonNullExample(@NonNull String name) { if (name == null) { throw new NullPointerException("name is marked non-null but is null"); } else { this.name = name; } } public static void main(String[] args) { new NonNullExample("test"); new NonNullExample((String)null); }}@Cleanup
当咱们在Java中应用资源时，不可避免地须要在应用后敞开资源。应用@Cleanup注解能够主动敞开资源。
/** * Created by macro on 2020/12/16. */public class CleanupExample { public static void main(String[] args) throws IOException { String inStr = "Hello World!"; //应用输入输出流主动敞开，无需编写try catch和调用close()办法 @Cleanup ByteArrayInputStream in = new ByteArrayInputStream(inStr.getBytes("UTF-8")); @Cleanup ByteArrayOutputStream out = new ByteArrayOutputStream(); byte[] b = new byte[1024]; while (true) { int r = in.read(b); if (r == -1) break; out.write(b, 0, r); } String outStr = out.toString("UTF-8"); System.out.println(outStr); }}编译后Lombok会生成如下代码。
public class CleanupExample { public CleanupExample() { } public static void main(String[] args) throws IOException { String inStr = "Hello World!"; ByteArrayInputStream in = new ByteArrayInputStream(inStr.getBytes("UTF-8")); try { ByteArrayOutputStream out = new ByteArrayOutputStream(); try { byte[] b = new byte[1024]; while(true) { int r = in.read(b); if (r == -1) { String outStr = out.toString("UTF-8"); System.out.println(outStr); 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
有了@Getter/@Setter注解，咱们再也不必编写getter/setter办法了。试想下之前即便咱们应用IDEA主动生成getter/setter办法，如果类属性的类型和名称改了，又要从新生成getter/setter办法也是一件很麻烦的事件。
/** * Created by macro on 2020/12/17. */public class GetterSetterExample { @Getter @Setter private String name; @Getter @Setter(AccessLevel.PROTECTED) private Integer age; public static void main(String[] args) { GetterSetterExample example = new GetterSetterExample(); example.setName("test"); example.setAge(20); System.out.printf("name:%s age:%d",example.getName(),example.getAge()); }}编译后Lombok会生成如下代码。
public class GetterSetterExample { private String name; private Integer age; public GetterSetterExample() { } public String getName() { return this.name; } public void setName(final String name) { this.name = name; } public Integer getAge() { return this.age; } protected void setAge(final Integer age) { this.age = age; }}@ToString
把所有类属性都编写到toString办法中不便打印日志，是一件如许枯燥无味的事件。应用@ToString注解能够主动生成toString办法，默认会蕴含所有类属性，应用@ToString.Exclude注解能够排除属性的生成。
/** * Created by macro on 2020/12/17. */@ToStringpublic class ToStringExample { @ToString.Exclude private Long id; private String name; private Integer age; public ToStringExample(Long id,String name,Integer age){ this.id =id; this.name = name; this.age = age; } public static void main(String[] args) { ToStringExample example = new ToStringExample(1L,"test",20); //主动实现toString办法，输入ToStringExample(name=test, age=20) System.out.println(example); }}编译后Lombok会生成如下代码。
public class ToStringExample { private Long id; private String name; private Integer age; public ToStringExample(Long id, String name, Integer age) { this.id = id; this.name = name; this.age = age; } public String toString() { return "ToStringExample(name=" + this.name + ", age=" + this.age + ")"; }}@EqualsAndHashCode
应用@EqualsAndHashCode注解能够主动生成hashCode和equals办法，默认蕴含所有类属性，应用@EqualsAndHashCode.Exclude能够排除属性的生成。
/** * Created by macro on 2020/12/17. */@Getter@Setter@EqualsAndHashCodepublic class EqualsAndHashCodeExample { private Long id; @EqualsAndHashCode.Exclude private String name; @EqualsAndHashCode.Exclude private Integer age; public static void main(String[] args) { EqualsAndHashCodeExample example1 = new EqualsAndHashCodeExample(); example1.setId(1L); example1.setName("test"); example1.setAge(20); EqualsAndHashCodeExample example2 = new EqualsAndHashCodeExample(); example2.setId(1L); //equals办法只比照id，返回true System.out.println(example1.equals(example2)); }}编译后Lombok会生成如下代码。
public class EqualsAndHashCodeExample { private Long id; private String name; private Integer age; public EqualsAndHashCodeExample() { } public boolean equals(final 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 { Object this$id = this.getId(); Object other$id = other.getId(); if (this$id == null) { if (other$id != null) { return false; } } else if (!this$id.equals(other$id)) { return false; } return true; } } } protected boolean canEqual(final Object other) { return other instanceof EqualsAndHashCodeExample; } public int hashCode() { int PRIME = true; int result = 1; Object $id = this.getId(); int result = result * 59 + ($id == null ? 43 : $id.hashCode()); return result; }}@XxConstructor
应用@XxConstructor注解能够主动生成构造方法，有@NoArgsConstructor、@RequiredArgsConstructor和@AllArgsConstructor三个注解能够应用。
- @NoArgsConstructor：生成无参构造函数。
- @RequiredArgsConstructor：生成蕴含必须参数的构造函数，应用@NonNull注解的类属性为必须参数。
- @AllArgsConstructor：生成蕴含所有参数的构造函数。
/** * Created by macro on 2020/12/17. */@NoArgsConstructor@RequiredArgsConstructor(staticName = "of")@AllArgsConstructorpublic class ConstructorExample { @NonNull private Long id; private String name; private Integer age; public static void main(String[] args) { //无参结构器 ConstructorExample example1 = new ConstructorExample(); //全副参数结构器 ConstructorExample example2 = new ConstructorExample(1L,"test",20); //@NonNull注解的必须参数结构器 ConstructorExample example3 = ConstructorExample.of(1L); }}编译后Lombok会生成如下代码。
public class ConstructorExample { @NonNull private Long id; private String name; private Integer age; public ConstructorExample() { } private ConstructorExample(@NonNull final Long id) { if (id == null) { throw new NullPointerException("id is marked non-null but is null"); } else { this.id = id; } } public static ConstructorExample of(@NonNull final Long id) { return new ConstructorExample(id); } public ConstructorExample(@NonNull final Long id, final String name, final Integer age) { if (id == null) { throw new NullPointerException("id is marked non-null but is null"); } else { this.id = id; this.name = name; this.age = age; } }}@Data
@Data是一个方便使用的组合注解，是@ToString、@EqualsAndHashCode、@Getter、@Setter和@RequiredArgsConstructor的组合体。
/** * Created by macro on 2020/12/17. */@Datapublic class DataExample { @NonNull private Long id; @EqualsAndHashCode.Exclude private String name; @EqualsAndHashCode.Exclude private Integer age; public static void main(String[] args) { //@RequiredArgsConstructor已失效 DataExample example1 = new DataExample(1L); //@Getter @Setter已失效 example1.setName("test"); example1.setAge(20); //@ToString已失效 System.out.println(example1); DataExample example2 = new DataExample(1L); //@EqualsAndHashCode已失效 System.out.println(example1.equals(example2)); }}编译后Lombok会生成如下代码。
public class DataExample { @NonNull private Long id; private String name; private Integer age; public DataExample(@NonNull final Long id) { if (id == null) { throw new NullPointerException("id is marked non-null but is null"); } else { this.id = id; } } @NonNull public Long getId() { return this.id; } public String getName() { return this.name; } public Integer getAge() { return this.age; } public void setId(@NonNull final Long id) { if (id == null) { throw new NullPointerException("id is marked non-null but is null"); } else { this.id = id; } } public void setName(final String name) { this.name = name; } public void setAge(final Integer age) { this.age = age; } public boolean equals(final Object o) { if (o == this) { return true; } else if (!(o instanceof DataExample)) { return false; } else { DataExample other = (DataExample)o; if (!other.canEqual(this)) { return false; } else { Object this$id = this.getId(); Object other$id = other.getId(); if (this$id == null) { if (other$id != null) { return false; } } else if (!this$id.equals(other$id)) { return false; } return true; } } } protected boolean canEqual(final Object other) { return other instanceof DataExample; } public int hashCode() { int PRIME = true; int result = 1; Object $id = this.getId(); int result = result * 59 + ($id == null ? 43 : $id.hashCode()); return result; } public String toString() { return "DataExample(id=" + this.getId() + ", name=" + this.getName() + ", age=" + this.getAge() + ")"; }}@Value
应用@Value注解能够把类申明为不可变的，申明后此类相当于final类，无奈被继承，其属性也会变成final属性。
/** * Created by macro on 2020/12/17. */@Valuepublic class ValueExample { private Long id; private String name; private Integer age; public static void main(String[] args) { //只能应用全参结构器 ValueExample example = new ValueExample(1L,"test",20); // example.setName("andy") //没有生成setter办法，会报错 // example.name="andy" //字段被设置为final类型，会报错 }}编译后Lombok会生成如下代码。
public final class ValueExample { private final Long id; private final String name; private final Integer age; public static void main(String[] args) { new ValueExample(1L, "test", 20); } public ValueExample(final Long id, final String name, final Integer age) { this.id = id; this.name = name; this.age = age; } public Long getId() { return this.id; } public String getName() { return this.name; } public Integer getAge() { return this.age; }}@Builder
应用@Builder注解能够通过建造者模式来创建对象，建造者模式加链式调用，创建对象太不便了！
/** * Created by macro on 2020/12/17. */@Builder@ToStringpublic class BuilderExample { private Long id; private String name; private Integer age; public static void main(String[] args) { BuilderExample example = BuilderExample.builder() .id(1L) .name("test") .age(20) .build(); System.out.println(example); }}编译后Lombok会生成如下代码。
public class BuilderExample { private Long id; private String name; private Integer age; BuilderExample(final Long id, final String name, final Integer age) { this.id = id; this.name = name; this.age = age; } public static BuilderExample.BuilderExampleBuilder builder() { return new BuilderExample.BuilderExampleBuilder(); } public String toString() { return "BuilderExample(id=" + this.id + ", name=" + this.name + ", age=" + this.age + ")"; } public static class BuilderExampleBuilder { private Long id; private String name; private Integer age; BuilderExampleBuilder() { } public BuilderExample.BuilderExampleBuilder id(final Long id) { this.id = id; return this; } public BuilderExample.BuilderExampleBuilder name(final String name) { this.name = name; return this; } public BuilderExample.BuilderExampleBuilder age(final Integer age) { this.age = age; return this; } public BuilderExample build() { return new BuilderExample(this.id, this.name, this.age); } public String toString() { return "BuilderExample.BuilderExampleBuilder(id=" + this.id + ", name=" + this.name + ", age=" + this.age + ")"; } }}@SneakyThrows
还在手动捕捉并抛出异样？应用@SneakyThrows注解主动实现试试！
/** * Created by macro on 2020/12/17. */public class SneakyThrowsExample { //主动抛出异样，无需解决 @SneakyThrows(UnsupportedEncodingException.class) public static byte[] str2byte(String str){ return str.getBytes("UTF-8"); } public static void main(String[] args) { String str = "Hello World!"; System.out.println(str2byte(str).length); }}编译后Lombok会生成如下代码。
public class SneakyThrowsExample { public SneakyThrowsExample() { } public static byte[] str2byte(String str) { try { return str.getBytes("UTF-8"); } catch (UnsupportedEncodingException var2) { throw var2; } }}@Synchronized
当咱们在多个线程中拜访同一资源时，往往会呈现线程平安问题，以前咱们往往应用synchronized关键字润饰办法来实现同步拜访。应用@Synchronized注解同样能够实现同步拜访。
package com.macro.mall.tiny.example;import lombok.*;/** * Created by macro on 2020/12/17. */@Datapublic class SynchronizedExample { @NonNull private Integer count; @Synchronized @SneakyThrows public void reduceCount(Integer id) { if (count > 0) { Thread.sleep(500); count--; System.out.println(String.format("thread-%d count:%d", id, count)); } } public static void main(String[] args) { //增加@Synchronized三个线程能够同步调用reduceCount办法 SynchronizedExample example = new SynchronizedExample(20); new ReduceThread(1, example).start(); new ReduceThread(2, example).start(); new ReduceThread(3, example).start(); } @RequiredArgsConstructor static class ReduceThread extends Thread { @NonNull private Integer id; @NonNull private SynchronizedExample example; @Override public void run() { while (example.getCount() > 0) { example.reduceCount(id); } } }}编译后Lombok会生成如下代码。
public class SynchronizedExample { private final Object $lock = new Object[0]; @NonNull private Integer count; public void reduceCount(Integer id) { try { synchronized(this.$lock) { if (this.count > 0) { Thread.sleep(500L); Integer var3 = this.count; Integer var4 = this.count = this.count - 1; System.out.println(String.format("thread-%d count:%d", id, this.count)); } } } catch (Throwable var7) { throw var7; } }}@With
应用@With注解能够实现对原对象进行克隆，并扭转其一个属性，应用时须要指定全参构造方法。
@With@AllArgsConstructorpublic class WithExample { private Long id; private String name; private Integer age; public static void main(String[] args) { WithExample example1 = new WithExample(1L, "test", 20); WithExample example2 = example1.withAge(22); //将原对象进行clone并设置age，返回false System.out.println(example1.equals(example2)); }}编译后Lombok会生成如下代码。
public class WithExample { private Long id; private String name; private Integer age; public WithExample withId(final Long id) { return this.id == id ? this : new WithExample(id, this.name, this.age); } public WithExample withName(final String name) { return this.name == name ? this : new WithExample(this.id, name, this.age); } public WithExample withAge(final Integer age) { return this.age == age ? this : new WithExample(this.id, this.name, age); } public WithExample(final Long id, final String name, final Integer age) { this.id = id; this.name = name; this.age = age; }}@Getter(lazy=true)
当咱们获取某一个属性比拟耗费资源时，能够给@Getter增加lazy=true属性实现懒加载，会生成Double Check Lock 样板代码对属性进行懒加载。
/** * Created by macro on 2020/12/17. */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; } public static void main(String[] args) { //应用Double Check Lock 样板代码对属性进行懒加载 GetterLazyExample example = new GetterLazyExample(); System.out.println(example.getCached().length); }}编译后Lombok会生成如下代码。
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) { 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
应用@Log注解，能够间接生成日志对象log，通过log对象能够间接打印日志。
/** * Created by macro on 2020/12/17. */@Logpublic class LogExample { public static void main(String[] args) { log.info("level info"); log.warning("level warning"); log.severe("level severe"); }}编译后Lombok会生成如下代码。
public class LogExample { private static final Logger log = Logger.getLogger(LogExample.class.getName()); public LogExample() { } public static void main(String[] args) { log.info("level info"); log.warning("level warning"); log.severe("level severe"); }}@Slf4j
应用Lombok生成日志对象时，依据应用日志实现的不同，有多种注解能够应用。比方@Log、@Log4j、@Log4j2、@Slf4j等。
/** * Created by macro on 2020/12/17. */@Slf4jpublic class LogSlf4jExample { public static void main(String[] args) { log.info("level:{}","info"); log.warn("level:{}","warn"); log.error("level:{}", "error"); }}编译后Lombok会生成如下代码。
public class LogSlf4jExample { private static final Logger log = LoggerFactory.getLogger(LogSlf4jExample.class); public LogSlf4jExample() { } public static void main(String[] args) { log.info("level:{}", "info"); log.warn("level:{}", "warn"); log.error("level:{}", "error"); }}Lombok原理
如果IDEA不装置Lombok插件的话，咱们关上应用Lombok的我的项目是无奈通过编译的。装了当前IDEA才会提醒咱们Lombok为咱们生成的办法和属性。
应用了@Data注解当前，查看类构造能够发现getter、setter、toString等办法。
关上target目录下的.class文件，咱们能够看到Lombok为咱们生成的代码，可见Lombok是通过解析注解，而后在编译时生成代码来实现Java代码的性能加强的。
参考资料
官网文档：https://projectlombok.org/fea...
我的项目源码地址
https://github.com/macrozheng...
本文 GitHub https://github.com/macrozheng/mall-learning 曾经收录，欢送大家Star！