关于java:Lombok有啥牛皮的SpringBoot和IDEA官方都要支持它

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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.
 */
@ToString
public 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
@EqualsAndHashCode
public 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")
@AllArgsConstructor
public 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.
 */
@Data
public 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.
 */
@Value
public 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
@ToString
public 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.
 */
@Data
public 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
@AllArgsConstructor
public 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.
 */
@Log
public 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.
 */
@Slf4j
public 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！

正文完
java
发表至： java
2020-12-31
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