第十三节:使用Lombok简化你的代码

[TOC]

在开发过程中，通常都会定义大量的JavaBean，然后通过IDE去产生其属性的构造器、getter、setter、equals、hashcode、toString方法，当要增加属性或者对某个属性进行改变时，比如命名、类型等，都需要重新去产生上面提到的这些方法。这样重复的劳动没有任何意义，Lombok里面的注解可以轻松解决这些问题。

• 官方地址：https://projectlombok.org/
• github地址：https://github.com/rzwitserloot/lombok

lombok实现的原理：主要是通过抽象语法树(AST)，在编译处理后，对应到有其注解的类，那么注解编译器就会自动去对应项目中的注解对应到在lombok语法树中的注解文件，并经过自动编译对应来产生对应类中的getter或者setter方法，达到简化代码的目的

pom.xml添加lombok

<dependency>
  <groupId>org.projectlombok</groupId>
  <artifactId>lombok</artifactId>
  <optional>true</optional>
</dependency>

@Getter @Setter注解

这一对注解从名字上就很好理解，用在成员变量前面，相当于为成员变量生成对应的get和set方法，同时还可以为生成的方法指定访问修饰符，当然，默认为public，直接来看下面的简单的例子：

// Rumenz.java
/**
 * @className: Rumenz
 * @description: TODO 类描述
 * @author: 入门小站 rumenz.com
 * @date: 2021/12/9
 **/
public class RumenzGetSet {
    @Getter @Setter
    private Integer id;
    @Getter @Setter
    private String name;

}

• 等价于

public class RumenzGetSet {
    private Integer id;
    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

@RestController
@RequestMapping("/rumenz")
public class RumenzController {

    @GetMapping("/index")
    public String index(){
        RumenzGetSet r=new RumenzGetSet();
        r.setId(1);
        r.setName("入门小站");

        return r.getId()+r.getName();
    }
}

访问http://127.0.0.1:8080/rumenz/index返回1入门小站

@NonNull注解

这个注解可以用在成员方法或者构造方法的参数前面，会自动产生一个关于此参数的非空检查，如果参数为空，则抛出一个空指针异常，举个例子来看看

public class RumenzNonNull {
    @Getter @Setter @NonNull
    private Integer id;
    @Getter @Setter @NonNull
    private String name;
}

• 等价于

public class RumenzNonNull {
    private Integer id;
    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        if (id == null) throw new java.lang.NullPointerException("id");
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        if (name == null) throw new java.lang.NullPointerException("name");
        this.name = name;
    }
}

@GetMapping("/index1")
public String index1(){
    RumenzNonNull r=new RumenzNonNull();
    r.setId(1);
    r.setName(null);

    return r.getId()+r.getName();
}

访问http://127.0.0.1:8080/rumenz/index1报错java.lang.NullPointerException: name is marked non-null but is null

@ToString

@ToString
public class RumenzToString {

    @Getter @Setter
    private Integer id;

    @Getter @Setter
    private String name;

    @Override
    public String toString() {
        return "RumenzToString{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

• 等价于

public class RumenzToString {

    private Integer id;

    private String name;


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "RumenzToString{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

@GetMapping("/index2")
public String index2(){
     RumenzToString r=new RumenzToString();
     r.setId(1);
     r.setName("入门小站");
     return r.toString();
}

访问http://127.0.0.1:8080/rumenz/index1返回RumenzToString{id=1, name='入门小站'}

EqualsAndHashCode注解

@EqualsAndHashCode
public class RumenzEqualsAndHashCode {

    @Getter @Setter
    private Integer id;
    @Getter @Setter
    private String name;

}

• 等价于

public class RumenzEqualsAndHashCode {
    private Integer id;
    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof RumenzEqualsAndHashCode)) return false;
        RumenzEqualsAndHashCode that = (RumenzEqualsAndHashCode) o;
        return id.equals(that.id) &&
                name.equals(that.name);
    }

}

@GetMapping("/index3")
public String index3(){
    RumenzEqualsAndHashCode r1=new RumenzEqualsAndHashCode();
    r1.setId(1);
    r1.setName("入门小站");

    RumenzEqualsAndHashCode r2=new RumenzEqualsAndHashCode();
    r2.setId(1);
    r2.setName("入门小站");
    if(r1.equals(r2)){
    return "相等";
    }
    return "不相等";
}

@Data注解

• 1）生成无参构造方法；
• 2）属性的set/get方法；
• 3）equals(), hashCode(), toString(), canEqual()方法。

@Data(staticConstructor="of")
public class RumenzData {


    private Integer id;

    private String name;

}
//等价于

public class RumenzData {
    private Integer id;
    private String name;

    private RumenzData() {
    }

    public static RumenzData of() {
        return new RumenzData();
    }

    public Integer getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public void setId(final Integer id) {
        this.id = id;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof RumenzData)) {
            return false;
        } else {
            RumenzData other = (RumenzData)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;
                }

                Object this$name = this.getName();
                Object other$name = other.getName();
                if (this$name == null) {
                    if (other$name != null) {
                        return false;
                    }
                } else if (!this$name.equals(other$name)) {
                    return false;
                }

                return true;
            }
        }
    }

    protected boolean canEqual(final Object other) {
        return other instanceof RumenzData;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $id = this.getId();
        int result = result * 59 + ($id == null ? 43 : $id.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

    public String toString() {
        return "RumenzData(id=" + this.getId() + ", name=" + this.getName() + ")";
    }
}

@GetMapping("/index4")
public String index4(){
   RumenzData of = RumenzData.of();
   of.setName("入门小站");
   String name = of.getName();
   return name;
}

@Cleanup注解

这个注解用在变量前面，可以保证此变量代表的资源会被自动关闭，默认是调用资源的close()方法，如果该资源有其它关闭方法，可使用@Cleanup(“methodName”)来指定要调用的方法，就用输入输出流来举个例子吧：

@GetMapping("/index5")
public String index5() throws IOException {

   File file = ResourceUtils.getFile("classpath:application.properties");
   @Cleanup  InputStream inputStream = new FileInputStream(file);

   byte b[]=new byte[(int) file.length()];
   inputStream.read(b);
   //@Cleanup 代替了 inputStream.close();
   return new String(b);
}

等价于

@GetMapping({"/index5"})
public String index5() throws IOException {
        File file = ResourceUtils.getFile("classpath:application.properties");
        FileInputStream inputStream = new FileInputStream(file);

        String var4;
        try {
            byte[] b = new byte[(int)file.length()];
            inputStream.read(b);
            var4 = new String(b);
        } finally {
            if (Collections.singletonList(inputStream).get(0) != null) {
                inputStream.close();
            }

        }

        return var4;
}

@NoArgsConstructor注解

@NoArgsConstructor在类上使用，它可以提供一个无参构造器

@NoArgsConstructor
public class RumenzNoArgsConstructor {
    private Integer id;
    private String name;
}

等价于

public class RumenzNoArgsConstructor {
    private Integer id;
    private String name;

    public RumenzNoArgsConstructor() {
    }
}

@RequiredArgsConstructor注解

指定final的属性生成构造方法

@ToString
@RequiredArgsConstructor
public class RumenzRequiredArgsConstructor {
    private Integer id;
    private final String name;
}

// 等价于

public class RumenzRequiredArgsConstructor {
    private Integer id;
    private final String name; //final

    public String toString() {
        return "RumenzRequiredArgsConstructor(id=" + this.id + ", name=" + this.name + ")";
    }

    public RumenzRequiredArgsConstructor(final String name) {
        this.name = name;
    }
}

@AllArgsConstructor注解

类中所有的字段都生成一个有参的构造方法.

@ToString
@AllArgsConstructor
public class RumenzAllArgsConstructor {
    private  Integer id;
    private  String name;
}

//等价于

public class RumenzAllArgsConstructor {
    private Integer id;
    private String name;

    public String toString() {
        return "RumenzAllArgsConstructor(id=" + this.id + ", name=" + this.name + ")";
    }

    public RumenzAllArgsConstructor(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }
}

@Value注解

• 1）有参构造方法；
• 2）只添加@Value注解，没有其他限制，那么类属性会被编译成final的，因此只有get方法，而没有set方法。

@ToString
@Value
public class RumenzValue {
    private Integer id;
    private String name;
}

// 等价于

public final class RumenzValue {
    private final Integer id;
    private final String name;

    public RumenzValue(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof RumenzValue)) {
            return false;
        } else {
            RumenzValue other = (RumenzValue)o;
            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;
            }

            Object this$name = this.getName();
            Object other$name = other.getName();
            if (this$name == null) {
                if (other$name != null) {
                    return false;
                }
            } else if (!this$name.equals(other$name)) {
                return false;
            }

            return true;
        }
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $id = this.getId();
        int result = result * 59 + ($id == null ? 43 : $id.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

    public String toString() {
        return "RumenzValue(id=" + this.getId() + ", name=" + this.getName() + ")";
    }
}

@SneakyThrows注解

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，很简单的注解，直接看个例子：

@SneakyThrows
@GetMapping("/index9")
public String index9() {

        //使用@SneakyThrows就不用显式抛出异常了
        File file = ResourceUtils.getFile("classpath:application.properties");
        @Cleanup  InputStream inputStream = new FileInputStream(file);

        byte b[]=new byte[(int) file.length()];
        inputStream.read(b);
        //@Cleanup 代替了 inputStream.close();
        return new String(b);
}

// 等价于

@GetMapping({"/index9"})
public String index9() {
        try {
            File file = ResourceUtils.getFile("classpath:application.properties");
            FileInputStream inputStream = new FileInputStream(file);

            String var4;
            try {
                byte[] b = new byte[(int)file.length()];
                inputStream.read(b);
                var4 = new String(b);
            } finally {
                if (Collections.singletonList(inputStream).get(0) != null) {
                    inputStream.close();
                }

            }

            return var4;
        } catch (Throwable var9) {
            throw var9;
        }
}

@Synchronized注解

synchronized是线程安全中一个重要的关键字，它是一种同步锁，主要用来保证在同一个时刻，只有一个线程可以执行某个方法或者某段代码块。一般使用synchronized去锁住代码块，而不是方法，因为锁住代码块效率更高。

public class RumenzSynchronized {

    private final Object readLock = new Object();

    @Synchronized
    public static void hello() {
        System.out.println("rumenz.com");
    }

    @Synchronized
    public int answerToLife() {
        return 110;
    }

    @Synchronized("readLock")
    public void foo() {
        System.out.println("入门小站");
    }
}

// 等价于

public class RumenzSynchronized {
    private static final Object $LOCK = new Object[0];
    private final Object $lock = new Object[0];
    private final Object readLock = new Object();

    public RumenzSynchronized() {
    }

    public static void hello() {
        synchronized($LOCK) {
            System.out.println("rumenz.com");
        }
    }

    public int answerToLife() {
        synchronized(this.$lock) {
            return 110;
        }
    }

    public void foo() {
        synchronized(this.readLock) {
            System.out.println("入门小站");
        }
    }
}

@Builder注解

用在类、构造器、方法上，为你提供复杂的builder APIs

@ToString
@Builder
public class RumenzBuilder {
    private Integer id;
    private String name;
}

// 等价于

public class RumenzBuilder {
    private Integer id;
    private String name;

    RumenzBuilder(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }

    public static RumenzBuilder.RumenzBuilderBuilder builder() {
        return new RumenzBuilder.RumenzBuilderBuilder();
    }

    public String toString() {
        return "RumenzBuilder(id=" + this.id + ", name=" + this.name + ")";
    }

    public static class RumenzBuilderBuilder {
        private Integer id;
        private String name;

        RumenzBuilderBuilder() {
        }

        public RumenzBuilder.RumenzBuilderBuilder id(final Integer id) {
            this.id = id;
            return this;
        }

        public RumenzBuilder.RumenzBuilderBuilder name(final String name) {
            this.name = name;
            return this;
        }

        public RumenzBuilder build() {
            return new RumenzBuilder(this.id, this.name);
        }

        public String toString() {
            return "RumenzBuilder.RumenzBuilderBuilder(id=" + this.id + ", name=" + this.name + ")";
        }
    }
}

@GetMapping("/index11")
public String index11() {
    RumenzBuilder rb=RumenzBuilder.builder().id(1).name("入门小站").build();
    return rb.toString();
}

@SuperBuilder

当实体类有集成关系时,需要用@SuperBuilder,否则调用的.builder都会报错.

@Builder并不支持父类成员属性的构造，@SuperBuilder注解的出现，就是用来解决这个问题。

使用@Builder或@SuperBuilder注解时，不会默认创建空参构造函数，如果你有额外使用空参构造函数或全参构造函数的需求，需要在子类和父类都加上以下注解：

本小结源码地址:

• GitHub:https://github.com/mifunc/springboot/tree/main/lession13
• Gitee:https://gitee.com/rumenz/springboot/tree/master/lession13
• https://rumenz.com/rumenbiji/springboot-lombok.html

介绍

• 我的博客 https://rumenz.com/ ,
• 我的工具箱 https://tooltt.com/