关于java:第十三节使用Lombok简化你的代码

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在开发过程中，通常都会定义大量的JavaBean，而后通过IDE去产生其属性的结构器、getter、setter、equals、hashcode、toString办法，当要减少属性或者对某个属性进行扭转时，比方命名、类型等，都须要从新去产生下面提到的这些办法。这样反复的劳动没有任何意义，Lombok外面的注解能够轻松解决这些问题。

• 官网地址：https://projectlombok.org/
• github地址：https://github.com/rzwitserlo...

lombok实现的原理：次要是通过形象语法树(AST)，在编译解决后，对应到有其注解的类，那么注解编译器就会主动去对应我的项目中的注解对应到在lombok语法树中的注解文件，并通过主动编译对应来产生对应类中的getter或者setter办法，达到简化代码的目标

pom.xml增加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了解，用在成员变量后面，相当于为成员变量生成对应的get和set办法，同时还能够为生成的办法指定拜访修饰符，当然，默认为public，间接来看上面的简略的例子：

// Rumenz.java/** * @className: Rumenz * @description: TODO 类形容 * @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();    }}

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

@NonNull注解

这个注解能够用在成员办法或者构造方法的参数后面，会主动产生一个对于此参数的非空查看，如果参数为空，则抛出一个空指针异样，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();}

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

@ToString

@ToStringpublic 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();}

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

EqualsAndHashCode注解

@EqualsAndHashCodepublic 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办法；
• 3）equals(), hashCode(), toString(), canEqual()办法。

@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

这个注解用在变量后面，能够保障此变量代表的资源会被主动敞开，默认是调用资源的close()办法，如果该资源有其它敞开办法，可应用@Cleanup(“methodName”)来指定要调用的办法，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在类上应用，它能够提供一个无参结构器

@NoArgsConstructorpublic 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@RequiredArgsConstructorpublic 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@AllArgsConstructorpublic 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）只增加@Value注解，没有其余限度，那么类属性会被编译成final的，因而只有get办法，而没有set办法。

@ToString@Valuepublic 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

这个注解用在办法上，能够将办法中的代码用try-catch语句包裹起来，捕捉异样并在catch中用Lombok.sneakyThrow(e)把异样抛出，能够应用@SneakyThrows(Exception.class)的模式指定抛出哪种异样，很简略的注解，间接看个例子：

@SneakyThrows@GetMapping("/index9")public String index9() {        //应用@SneakyThrows就不必显式抛出异样了        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是线程平安中一个重要的关键字，它是一种同步锁，次要用来保障在同一个时刻，只有一个线程能够执行某个办法或者某段代码块。个别应用synchronized去锁住代码块，而不是办法，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、结构器、办法上，为你提供简单的builder APIs

@ToString@Builderpublic 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,须要用@SuperBuilder,否则调用的.builder都会报错.

@Builder并不反对父类成员属性的结构，@SuperBuilder注解的呈现，就是用来解决这个问题。

应用@Builder或@SuperBuilder注解时，不会默认创立空参构造函数，如果你有额定应用空参构造函数或全参构造函数的需要，须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/spr...
• Gitee:https://gitee.com/rumenz/spri...
• https://rumenz.com/rumenbiji/...

介绍

• 我的博客 https://rumenz.com/ ,
• 我的工具箱 https://tooltt.com/
• 微信公众号:【入门小站】

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