lombok 通过注解消除实际开发中的样板式代码：getter、setter 方法，重写 toString、equals 方法等。
注解
@NonNull
@NonNull
@NonNull 注解可以放在方法，参数或字段上。
该注解不是断言非空，而是在赋值该字段时对参数进行判空检查，如果已经有了 if (xxx == null) 则不会有其他操作。
With Lombok
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| import lombok.NonNull;
public class NonNullExample extends Something {
private String name;
public NonNullExample(@NonNull Person person) {
super("Hello");
this.name = person.getName();
}
}
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Vanilla Java
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| import lombok.NonNull;
public class NonNullExample extends Something {
private String name;
public NonNullExample(@NonNull Person person) {
super("Hello");
if (person == null) {
throw new NullPointerException("person is marked non-null but is null");
}
this.name = person.getName();
}
}
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@Cleanup
@Cleanup
自动调用 close() 方法，如果还需要做异常处理，明显不如 try-with 方便。
With Lombok
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import lombok.Cleanup;
import java.io.*;
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);
}
}
}
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Vanilla Java
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| import java.io.*;
public class CleanupExample {
public static void main(String[] args) throws IOException {
InputStream in = new FileInputStream(args[0]);
try {
OutputStream out = new FileOutputStream(args[1]);
try {
byte[] b = new byte[10000];
while (true) {
int r = in.read(b);
if (r == -1) break;
out.write(b, 0, r);
}
} finally {
if (out != null) {
out.close();
}
}
} finally {
if (in != null) {
in.close();
}
}
}
}
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@Getter/@Setter
@Getter and @Setter
自动生成属性的 get/set 方法，默认都是 public，可通过 AccessLevel 设置可见性。
- 作用类上，生成所有非静态成员变量的 getter/setter 方法
- 作用于成员变量上，生成该成员变量的 getter/setter 方法
- Getter(lazy=true) 懒加载
With Lombok
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| import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;
public class GetterSetterExample {
@Getter @Setter private int age = 10;
@Setter(AccessLevel.PROTECTED) private String name;
@Override
public String toString() {
return String.format("%s (age: %d)", name, age);
}
}
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Vanilla Java
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| public class GetterSetterExample {
private int age = 10;
private String name;
@Override
public String toString() {
return String.format("%s (age: %d)", name, age);
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
protected void setName(String name) {
this.name = name;
}
}
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@ToString
@ToString
作用于类，覆盖默认的 toString() 方法。
- 通过 includeFieldNames 属性限定显示某些字段
- 通过 exclude 属性排除某些字段
- callSuper 是否输出超类
With Lombok
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| import lombok.ToString;
@ToString
public class ToStringExample {
private static final int STATIC_VAR = 10;
private String name;
private Shape shape = new Square(5, 10);
private String[] tags;
@ToString.Exclude private int id;
public String getName() {
return this.name;
}
@ToString(callSuper=true, includeFieldNames=true)
public static class Square extends Shape {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
}
}
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import java.util.Arrays;
public class ToStringExample {
private static final int STATIC_VAR = 10;
private String name;
private Shape shape = new Square(5, 10);
private String[] tags;
private int id;
public String getName() {
return this.name;
}
public static class Square extends Shape {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
@Override public String toString() {
return "Square(super=" + super.toString() + ", width=" + this.width + ", height=" + this.height + ")";
}
}
@Override public String toString() {
return "ToStringExample(" + this.getName() + ", " + this.shape + ", " + Arrays.deepToString(this.tags) + ")";
}
}
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@EqualsAndHashCode
@EqualsAndHashCode
作用于类，覆盖默认的 equals 和 hashCode。
doNotUseGetters = [true | false] (default: false)callSuper = [call | skip | warn] (default: warn)flagUsage = [warning | error] (default: not set)
With Lombok
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| import lombok.EqualsAndHashCode;
@EqualsAndHashCode
public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
@EqualsAndHashCode.Exclude private Shape shape = new Square(5, 10);
private String[] tags;
@EqualsAndHashCode.Exclude private int id;
public String getName() {
return this.name;
}
@EqualsAndHashCode(callSuper=true)
public static class Square extends Shape {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
}
}
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Vanilla Java
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| import java.util.Arrays;
public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
private Shape shape = new Square(5, 10);
private String[] tags;
private int id;
public String getName() {
return this.name;
}
@Override
public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof EqualsAndHashCodeExample)) return false;
EqualsAndHashCodeExample other = (EqualsAndHashCodeExample) o;
if (!other.canEqual((Object)this)) return false;
if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
if (Double.compare(this.score, other.score) != 0) return false;
if (!Arrays.deepEquals(this.tags, other.tags)) return false;
return true;
}
@Override
public int hashCode() {
final int PRIME = 59;
int result = 1;
final long temp1 = Double.doubleToLongBits(this.score);
result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());
result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
result = (result*PRIME) + Arrays.deepHashCode(this.tags);
return result;
}
protected boolean canEqual(Object other) {
return other instanceof EqualsAndHashCodeExample;
}
public static class Square extends Shape {
private final int width, height;
public Square(int width, int height) {
this.width = width;
this.height = height;
}
@Override
public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof Square)) return false;
Square other = (Square) o;
if (!other.canEqual((Object)this)) return false;
if (!super.equals(o)) return false;
if (this.width != other.width) return false;
if (this.height != other.height) return false;
return true;
}
@Override
public int hashCode() {
final int PRIME = 59;
int result = 1;
result = (result*PRIME) + super.hashCode();
result = (result*PRIME) + this.width;
result = (result*PRIME) + this.height;
return result;
}
protected boolean canEqual(Object other) {
return other instanceof Square;
}
}
}
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@NoArgsConstructor, @RequiredArgsConstructor And @AllArgsConstructor
@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor
生成各种构造函数，看名字知用途，其中 @RequiredArgsConstructor 通过 @NonNull 获取需要构造的属性。
With Lombok
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| import lombok.AccessLevel;
import lombok.RequiredArgsConstructor;
import lombok.AllArgsConstructor;
import lombok.NonNull;
@RequiredArgsConstructor(staticName = "of")
@AllArgsConstructor(access = AccessLevel.PROTECTED)
public class ConstructorExample<T> {
private int x, y;
@NonNull private T description;
@NoArgsConstructor
public static class NoArgsExample {
@NonNull private String field;
}
}
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| public class ConstructorExample<T> {
private int x, y;
@NonNull private T description;
private ConstructorExample(T description) {
if (description == null) throw new NullPointerException("description");
this.description = description;
}
public static <T> ConstructorExample<T> of(T description) {
return new ConstructorExample<T>(description);
}
@java.beans.ConstructorProperties({"x", "y", "description"})
protected ConstructorExample(int x, int y, T description) {
if (description == null) throw new NullPointerException("description");
this.x = x;
this.y = y;
this.description = description;
}
public static class NoArgsExample {
@NonNull private String field;
public NoArgsExample() {
}
}
}
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@Data
@Data
作用于类上，是以下注解的集合：
@ToString @EqualsAndHashCode @Getter @Setter @RequiredArgsConstructor
@Value
@Value
用于一个不可变的对象类，区别于 @Data 在于没有 @Setter，属性默认 final，构造函数是 @AllArgsConstructor。
@Builder
@Builder
作用于类上，将类转变为建造者模式。
With Lombok
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| import lombok.Builder;
import lombok.Singular;
import java.util.Set;
@Builder
public class BuilderExample {
@Builder.Default private long created = System.currentTimeMillis();
private String name;
private int age;
@Singular private Set<String> occupations;
}
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| import java.util.Set;
public class BuilderExample {
private long created;
private String name;
private int age;
private Set<String> occupations;
BuilderExample(String name, int age, Set<String> occupations) {
this.name = name;
this.age = age;
this.occupations = occupations;
}
private static long $default$created() {
return System.currentTimeMillis();
}
public static BuilderExampleBuilder builder() {
return new BuilderExampleBuilder();
}
public static class BuilderExampleBuilder {
private long created;
private boolean created$set;
private String name;
private int age;
private java.util.ArrayList<String> occupations;
BuilderExampleBuilder() {
}
public BuilderExampleBuilder created(long created) {
this.created = created;
this.created$set = true;
return this;
}
public BuilderExampleBuilder name(String name) {
this.name = name;
return this;
}
public BuilderExampleBuilder age(int age) {
this.age = age;
return this;
}
public BuilderExampleBuilder occupation(String occupation) {
if (this.occupations == null) {
this.occupations = new java.util.ArrayList<String>();
}
this.occupations.add(occupation);
return this;
}
public BuilderExampleBuilder occupations(Collection<? extends String> occupations) {
if (this.occupations == null) {
this.occupations = new java.util.ArrayList<String>();
}
this.occupations.addAll(occupations);
return this;
}
public BuilderExampleBuilder clearOccupations() {
if (this.occupations != null) {
this.occupations.clear();
}
return this;
}
public BuilderExample build() {
Set<String> occupations = ...;
return new BuilderExample(created$set ? created : BuilderExample.$default$created(), name, age, occupations);
}
@java.lang.Override
public String toString() {
return "BuilderExample.BuilderExampleBuilder(created = " + this.created + ", name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")";
}
}
}
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@SneakyThrows
@SneakyThrows
可以对受检异常进行捕捉并抛出，根据官方介绍大概抛出之前没检查的异常。
To boldly throw checked exceptions where no one has thrown them before!
With Lombok
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| import lombok.SneakyThrows;
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();
}
}
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Vanilla Java
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| import lombok.Lombok;
public class SneakyThrowsExample implements Runnable {
public String utf8ToString(byte[] bytes) {
try {
return new String(bytes, "UTF-8");
} catch (UnsupportedEncodingException e) {
throw Lombok.sneakyThrow(e);
}
}
public void run() {
try {
throw new Throwable();
} catch (Throwable t) {
throw Lombok.sneakyThrow(t);
}
}
}
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@Synchronized
@Synchronized
作用于方法级别，可以替换 synchronize 关键字或 lock 锁，用处不大。
With Lombok
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import lombok.Synchronized;
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");
}
}
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| public class SynchronizedExample {
private static final Object $LOCK = new Object[0];
private final Object $lock = new Object[0];
private final Object readLock = new Object();
public static void hello() {
synchronized($LOCK) {
System.out.println("world");
}
}
public int answerToLife() {
synchronized($lock) {
return 42;
}
}
public void foo() {
synchronized(readLock) {
System.out.println("bar");
}
}
}
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@With
@With
克隆对象，修改一个值而保留其他值不变。
With Lombok
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| import lombok.AccessLevel;
import lombok.NonNull;
import lombok.With;
public class WithExample {
@With(AccessLevel.PROTECTED) @NonNull private final String name;
@With private final int age;
public WithExample(@NonNull String name, int age) {
this.name = name;
this.age = age;
}
}
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| import lombok.NonNull;
public class WithExample {
private @NonNull final String name;
private final int age;
public WithExample(String name, int age) {
if (name == null) throw new NullPointerException();
this.name = name;
this.age = age;
}
protected WithExample withName(@NonNull String name) {
if (name == null) throw new java.lang.NullPointerException("name");
return this.name == name ? this : new WithExample(name, age);
}
public WithExample withAge(int age) {
return this.age == age ? this : new WithExample(name, age);
}
}
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@Log
@Log (and friends)
作用于类上，生成日志变量。
针对不同的日志实现产品，有不同的注解。
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| @Log4j
private static final org.apache.log4j.Logger log = org.apache.log4j.Logger.getLogger(LogExample.class);
@Slf4j
private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class);
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SLF4J (Simple logging Facade for Java) 不是一个真正的日志实现，而是一个抽象层（ abstraction layer），它允许你在后台使用任意一个日志类库。
语法糖
Val
val
用在局部变量前面，声明为 final 常量。
Var
var
用在局部变量前面，声明变量。
实验性
更多开发中的功能详见：
Experimental