Lombok - 快速入门

1. val

自动识别循环变量类型

本地变量和foreach循环可用。

import java.util.ArrayList;
import java.util.HashMap;
import lombok.val;

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");
    //直接使用val即可遍历
    for (val entry : map.entrySet()) {
      System.out.printf("%d: %s\n", entry.getKey(), entry.getValue());
    }
  }
}

2. @NonNull

自动检查该变量是否为null，若为null则抛出NullPointerException异常

import lombok.NonNull;

public class NonNullExample extends Something {
  private String name;

  public NonNullExample(@NonNull Person person) {
    super("Hello");
    this.name = person.getName();
  }
}

等同于

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();
  }
}

3. @Cleanup

使用@Clean可以自动关闭流资源

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);
    }
  }
}

等同于

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();
      }
    }
  }
}

4. @Getter and @Setter

自动生成对应的 getter 方法和 setter 方法

import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;

public class GetterSetterExample {
  /**
   * Age of the person. Water is wet.
   *
   * @param age New value for this person's age. Sky is blue.
   * @return The current value of this person's age. Circles are round.
   */
  @Getter @Setter private int age = 10;

  /**
   * Name of the person.
   * -- SETTER --
   * Changes the name of this person.
   *
   * @param name The new value.
   */
  @Setter(AccessLevel.PROTECTED) private String name;

  @Override public String toString() {
    return String.format("%s (age: %d)", name, age);
  }
}

@Getter(lazy=true)

该注释可以缓存第一次访问getter方法的值，后续使用getter都是第一次访问getter的值

5. @ToString

自动生成 toString 方法

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;
    }
  }
}

6. @EqualsAndHashCode

自动生成 equals 方法和 hashCode 方法

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;
    }
  }
}

7. @NoArgsConstructor and @AllArgsConstructor

自动生成无参构造器和全参构造器

可选参数access

access = AccessLevel.PROTECTED等

import lombok.NoArgsConstructor;
import lombok.AllArgsConstructor;

@NoArgsConstructor
@AllArgsConstructor
public class ConstructorExample {

    private Integer id;

    private String name;
}

8. @RequiredArgsConstructor

Lombok提供的自动注入，注入的对象的字段全部需要是 final 的。

可能会造成循环依赖，慎用。

import lombok.RequiredArgsConstructor;

@RequiredArgsConstructor(staticName = "pocket")
public class ConstructorExample {

    private Integer id;

    private String name;
}

9. @Data

复合注解，包含以下注解：@ToString,@EqualsAndHashCode,@Getter,@Setter,@RequiredArgsConstructor

import lombok.AccessLevel;
import lombok.Setter;
import lombok.Data;
import lombok.ToString;

@Data
public class DataExample {
  private final String name;
  @Setter(AccessLevel.PACKAGE) private int age;
  private double score;
  private String[] tags;

  @ToString(includeFieldNames=true)
  @Data(staticConstructor="of")
  public static class Exercise<T> {
    private final String name;
    private final T value;
  }
}

10. @Value

作用于类，使所有的成员变量都是 final 的

import lombok.AccessLevel;
import lombok.experimental.NonFinal;
import lombok.experimental.Value;
import lombok.experimental.With;
import lombok.ToString;

@Value public class ValueExample {
  String name;
  @With(AccessLevel.PACKAGE) @NonFinal int age;
  double score;
  protected String[] tags;

  @ToString(includeFieldNames=true)
  @Value(staticConstructor="of")
  public static class Exercise<T> {
    String name;
    T value;
  }
}

11. @Builder

作用于类，使之可以链式注入属性

Person.builder()
	.name("Adam Savage")
	.city("San Francisco")
	.job("Mythbusters")
	.job("Unchained Reaction")
	.build();

12. @SneakyThrows

减少异常处理，直接抛出异常即可，无需处理

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();
  }
}

等同于

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);
    }
  }
}

13. @Synchronized

只能作用于方法，为方法操作添加代码块

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");
  }
}

等同于

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");
    }
  }
}

14. @With

可以作用于类和成员变量，返回复制后的对象

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;
  }
}

等同于

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);
  }
}

15. @Log类

使用后可直接使用对应的 log 方法

@CommonsLog

@Flogger

@JBossLog

@Log

@Log4j

@Log4j2

@Slf4j

@XSlf4j

@CustomLog

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");
  }
}

等同于

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");
  }
}