lombok 简化 Java 代码

发布日期:2019-06-16

title: lombok 简化 Java 代码date: 2018-10-20 20:32:19tags: lombokauthor :辰砂tj


1.介绍

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)。它通过注解实现这一目的。Lombok官网:https://projectlombok.org

2.idea使用

1.引入依赖

在项目中添加Lombok依赖jar,在pom文件中添加如下部分。(不清楚版本可以在Maven仓库中搜索)

<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok --><dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.16.18</version> <scope>provided</scope></dependency>

2.idea插件

3.注解的说明

@NonNull

or: How I learned to stop worrying and love the NullPointerException.该注解使用在属性上,该注解用于属的非空检查,当放在setter方法的字段上,将生成一个空检查,如果为空,则抛出NullPointerException。该注解会默认是生成一个无参构造。

public class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid @NonNull @Setter @Getter private String username private boolean flag}

如果测试的时候username为空的情况下结果如下:

Exception in thread "main" java.lang.NullPointerException: username at com.taojian.tblog.lombok.User.setUsername(User.java:28) at com.taojian.tblog.lombok.Test.main(Test.java:15)

@Cleanup

Automatic resource management: Call your close() methods safely with no hassle.该注解使用在属性前,该注解是用来保证分配的资源被释放。在本地变量上使用该注解,任何后续代码都将封装在try/finally中,确保当前作用于中的资源被释放。默认@Cleanup清理的方法为close,可以使用value指定不同的方法名称

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() } } }}

使用后:

import lombok.Cleanupimport 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) } }}

@Getter/@Setter

Never write public int getFoo() {return foo} again.@Getter 就相对于是属性的get()方法,@Setter就相当于属性的set()方法。

The generated getter/setter method will be public unless you explicitly specify an AccessLevel as shown in the example below. Legal access levels are PUBLIC PROTECTED PACKAGE and PRIVATE.这句话的意思就是可以指定设置的getter,setter的方法的权限, @Setter(AccessLevel.PROTECTED) 这个就表示是一个protected属性。

@Setter(AccessLevel.PROTECTED) private String name /** * Changes the name of this person. * * @param name The new value. */ protected void setName(String name) { this.name = name }

使用前:

public class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private String password public Integer getUid() { return uid } public String getUsername() { return username } public String getPassword() { return password } public void setUid(Integer uid) { this.uid = uid } public void setUsername(String username) { this.username = username } public void setPassword(String password) { this.password = password }}

使用后:

@Getter@Setterpublic class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private String password}

@ToString

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

1、如果需要可以通过注释参数includeFieldNames来控制输出中是否包含的属性名称。2、可以通过exclude参数中包含字段名称,可以从生成的方法中排除特定字段。3、可以通过callSuper参数控制父类的输出。

@ToString(exclude="column")

意义:排除column列所对应的元素,即在生成toString方法时不包含column参数;

@ToString(exclude={"column1""column2"})

意义:排除多个column列所对应的元素,其中间用英文状态下的逗号进行分割,即在生成toString方法时不包含多个column参数;

@ToString(of="column")

意义:只生成包含column列所对应的元素的参数的toString方法,即在生成toString方法时只包含column参数;;

@ToString(of={"column1""column2"})

意义:只生成包含多个column列所对应的元素的参数的toString方法,其中间用英文状态下的逗号进行分割,即在生成toString方法时只包含多个column参数;

使用前:

public class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private String password @Override public String toString() { return super.toString() }}

使用后:

@ToStringpublic class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private String password

@EqualsAndHashCode

Equality made easy: Generates hashCode and equals implementations from the fields of your object..可以使用@EqualsAndHashCodelombok生成equals(Object other)和hashCode()方法的实现来注释任何类定义作用于类,自动重写类的equals()、hashCode()方法。常用的参数有exclude(指定方法中不包含的属性)、callSuper(方法中是否包含父类ToString()方法返回的值)使用前:

使用后:

import lombok.EqualsAndHashCode@EqualsAndHashCodepublic 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 } // 因为有继承的关系,所以要设置true,如果没有,只继承了Object类的时候,就会报错 @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 } }}

使用后:

import java.util.Arrayspublic 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 } }}

@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.@NoArgsConstructor 相对于:

public User(){}

@RequiredArgsConstructor 该注解使用在类上,使用类中所有带有 @NonNull 注解的或者带有 final 修饰的成员变量生成对应的构造方法。

@NoArgsConstructor 相对于:

public User(Integer uid String username boolean flag) { this.uid = uid this.username = username this.flag = flag }

@Data

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

该注解使用在类上,该注解是最常用的注解,它结合了@ToString,@EqualsAndHashCode, @Getter和@Setter。本质上使用@Data注解,类默认@ToString和@EqualsAndHashCode以及每个字段都有@Setter和@getter。该注解也会生成一个公共构造函数,可以将任何@NonNull和final字段作为参数。

虽然@Data注解非常有用,但是它没有与其他注解相同的控制粒度。@Data提供了一个可以生成静态工厂的单一参数,将staticConstructor参数设置为所需要的名称,Lombok自动生成的构造函数设置为私有,并提供公开的给定名称的静态工厂方法。

/** * @description: * @author: taojian * @create: 2018-09-30 22:32 * 实际上含有这些方法 * getUid * getUsername * isFlag 这里是isFlag(),而不是getFlag() * setUid * setUsername * setFlag * equals * hashCode * canEqual * toString **/@Datapublic class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private boolean flag@Datapublic class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private boolean flag}

@Value

Immutable classes made very easy.这个注解用在 类 上,会生成含所有参数的构造方法,get 方法,此外还提供了equals、hashCode、toString 方法。 注意:没有setter 类似@Data

/** * @description: * @author: taojian * @create: 2018-09-30 22:32 * User * getUid * getUsername * isFlag * equals * hashCode * toString * serialVersionUID * uid * username * flag **/@Valuepublic class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private boolean flag}

@Builder

... and Bob"s your uncle: No-hassle fancy-pants APIs for object creation!Project Lombok的@Builder 是一种在不编写样板代码的情况下使用Builder模式的有用机制。我们可以将此注释应用于 类 或方法。

在类上使用@Builder

/** * @description: * User * getUid * getUsername * isFlag * builder 这个方法是增加的方法 **/@Getter@Builderpublic class User implements Serializable { private static final long serialVersionUID = 1L private Integer uid private String username private boolean flag}

public class Test { public static void main(String[] args) { User user = User.builder().username("taojian").flag(true).uid(1).build() System.out.println(user.getUsername().equals("taojian")) // true }}

2. 在方法上使用@Builder

假设我们正在使用我们想要使用构建器构造的对象,但我们无法修改源或扩展类。

首先,让我们使用Lombok的@Value注释创建一个快速示例:

@Valuefinal class ImmutableClient { private int id private String name}

现在我们有一个带有两个不可变成员的最终 类,它们的getter和一个all-arguments构造函数。

我们介绍了如何在Class上 使用@Builder,但我们也可以在方法上使用它。我们将使用此功能来解决无法修改或扩展ImmutableClient的问题。

接下来,我们将使用创建ImmutableClients的方法创建一个新类:

class ClientBuilder { @Builder(builderMethodName = "builder") public static ImmutableClient newClient(int id String name) { return new ImmutableClient(id name) }}

这个注解创建了一个名为法生成器()是返回一个生成器来创建ImmutableClients。

现在我们可以构建一个ImmutableClient:

ImmutableClient testImmutableClient = ClientBuilder.builder() .name("foo") .id(1) .build()assertThat(testImmutableClient.getName()) .isEqualTo("foo")assertThat(testImmutableClient.getId()) .isEqualTo(1)

@SneakyThrows

To boldly throw checked exceptions where no one has thrown them before!该注解使用在方法上,这个注解用在 方法 上,可以将方法中的代码用 try-catch 语句包裹起来,捕获异常并在 catch 中用 Lombok.sneakyThrow(e) 把异常抛出,可以使用 @SneakyThrows(Exception.class) 的形式指定抛出哪种异常。该注解需要谨慎使用

使用前:

import lombok.Lombokpublic 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) } }}

使用后:

import lombok.SneakyThrowspublic 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() }}

@Synchronized

synchronized done right: Don"t expose your locks.该注解使用在类或者实例方法上,Synchronized在一个方法上,使用关键字可能会导致结果和想要的结果不同,因为多线程情况下会出现异常情况。Synchronized关键字将在this示例方法情况下锁定当前对象,或者class讲台方法的对象上多锁定。这可能会导致死锁现象。一般情况下建议锁定一个专门用于此目的的独立锁,而不是允许公共对象进行锁定。该注解也是为了达到该目的。

使用前:

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") } }}

使用后:

mport lombok.Synchronizedpublic 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") }}

@Log @Slf4j

Captain"s Log stardate 24435.7: "What was that line again?"日志类型experimentalHead to the lab: The new stuff we"re working on.

@CommonsLogCreates private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog(LogExample.class)@FloggerCreates private static final com.google.common.flogger.FluentLogger log = com.google.common.flogger.FluentLogger.forEnclosingClass()@JBossLogCreates private static final org.jboss.logging.Logger log = org.jboss.logging.Logger.getLogger(LogExample.class)@LogCreates private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName())@Log4jCreates private static final org.apache.log4j.Logger log = org.apache.log4j.Logger.getLogger(LogExample.class)@Log4j2Creates private static final org.apache.logging.log4j.Logger log = org.apache.logging.log4j.LogManager.getLogger(LogExample.class)@Slf4jCreates private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class)@XSlf4jCreates private static final org.slf4j.ext.XLogger log = org.slf4j.ext.XLoggerFactory.getXLogger(LogExample.class)

使用前:

public class LogExample { private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName()) public static void main(String... args) { log.severe("Something"s wrong here") }}public class LogExampleOther { private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExampleOther.class) public static void main(String... args) { log.error("Something else is wrong here") }}public class LogExampleCategory { private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog("CounterLog") public static void main(String... args) { log.error("Calling the "CounterLog" with a message") }}

使用后:

import lombok.extern.java.Logimport lombok.extern.slf4j.Slf4j@Logpublic class LogExample { public static void main(String... args) { log.severe("Something"s wrong here") }}@Slf4jpublic class LogExampleOther { public static void main(String... args) { log.error("Something else is wrong here") }}@CommonsLog(topic="CounterLog")public class LogExampleCategory { public static void main(String... args) { log.error("Calling the "CounterLog" with a message") }}

参考文章链接:

https://www.baeldung.com/lombok-builder

https://blog.csdn.net/motui/article/details/79012846

https://blog.csdn.net/motui/article/details/79012846

https://projectlombok.org/

https://segmentfault.com/a/1190000005133786