lombok 简化 Java 代码


title: lombok 简化 Java 代码
date: 2018-10-20 20:32:19
tags: lombok
author :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

在这里插入图片描述
在这里插入图片描述

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.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);
    }
  }
}

@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
@Setter
public 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:

@ToString
public 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;

@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;
  }
  // 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.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;
    }
  }
}

@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
 **/
@Data
public class User implements Serializable {

    private static final long serialVersionUID = 1L;

    private Integer uid;

    private String username;

    private boolean flag;


@Data
public 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
 **/

@Value
public 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
@Builder
public 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:

@Value
final 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.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);
    }
  }
}

使用后:


 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();
  }
}

@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.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");
  }
}

@Log @Slf4j

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

@CommonsLog
Creates private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog(LogExample.class);
@Flogger
Creates private static final com.google.common.flogger.FluentLogger log = com.google.common.flogger.FluentLogger.forEnclosingClass();
@JBossLog
Creates private static final org.jboss.logging.Logger log = org.jboss.logging.Logger.getLogger(LogExample.class);
@Log
Creates private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName());
@Log4j
Creates private static final org.apache.log4j.Logger log = org.apache.log4j.Logger.getLogger(LogExample.class);
@Log4j2
Creates private static final org.apache.logging.log4j.Logger log = org.apache.logging.log4j.LogManager.getLogger(LogExample.class);
@Slf4j
Creates private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class);
@XSlf4j
Creates 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.Log;
import lombok.extern.slf4j.Slf4j;

@Log
public class LogExample {
  
  public static void main(String... args) {
    log.severe("Something's wrong here");
  }
}

@Slf4j
public 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


欢迎大家关注我的公众号,会定期给大家更新一些新的文章,和一些新的看法。互相交流

posted @ 2018-10-20 20:04 辰砂tj 阅读(...) 评论(...) 编辑 收藏