SpringBoot - Lombok使用详解5（@log、@Buinder、@SneakyThrows、@Synchronized）

七、Lombok注解详解（5）

12，@log

（1）该注解用在类上，可以省去从日志工厂生成日志对象这一步，直接进行日志记录，具体注解根据日志工具的不同而不同。不同的日志注解总结如下（上面是注解，下面是实际作用）：

我们也可以在注解中使用 topic 来指定生成 log 对象时的类名。

 1 @CommonsLog
 2 private static final org.apache.commons.logging.Log log =
 3         org.apache.commons.logging.LogFactory.getLog(LogExample.class);
 4
 5 @JBossLog
 6 private static final org.jboss.logging.Logger log =
 7         org.jboss.logging.Logger.getLogger(LogExample.class);
 8
 9 @Log
10 private static final java.util.logging.Logger log =
11         java.util.logging.Logger.getLogger(LogExample.class.getName());
12
13 @Log4j
14 private static final org.apache.log4j.Logger log =
15         org.apache.log4j.Logger.getLogger(LogExample.class);
16
17 @Log4j2
18 private static final org.apache.logging.log4j.Logger log =
19         org.apache.logging.log4j.LogManager.getLogger(LogExample.class);
20
21 @Slf4j
22 private static final org.slf4j.Logger log =
23         org.slf4j.LoggerFactory.getLogger(LogExample.class);
24
25 @XSlf4j
26 private static final org.slf4j.ext.XLogger log =
27         org.slf4j.ext.XLoggerFactory.getXLogger(LogExample.class);

（2）下面是一个简单的使用样例：

 1 // 使用注解
 2 @Log
 3 public class LogExample {
 4     public static void main(String... args) {
 5         log.error("Something's wrong here");
 6     }
 7 }
 8
 9 // 不使用注解
10 public class LogExample {
11     private static final java.util.logging.Logger log =
12             java.util.logging.Logger.getLogger(LogExample.class.getName());
13
14     public static void main(String... args) {
15         log.error("Something's wrong here");
16     }
17 }

13，@Buinder

（1）builder 是现在比较推崇的一种构建值对象的方式。该描述符用于将类改造成 builder（建造者）模式，用在类、方法或者构造函数上。

 1 package com.example.demo;
 2
 3 import lombok.Builder;
 4 import lombok.Singular;
 5
 6 import java.util.Set;
 7
 8 @Builder
 9 public class BuilderExample {
10     private String name;
11     private int age;
12     @Singular
13     private Set<String> occupations;
14 }

（2）上面相当于如下传统的 Java 代码：

 1 package com.example.demo;
 2
 3 import java.util.Collection;
 4 import java.util.Set;
 5
 6 public class BuilderExample {
 7     private String name;
 8     private int age;
 9     private Set<String> occupations;
10
11     BuilderExample(String name, int age, Set<String> occupations) {
12         this.name = name;
13         this.age = age;
14         this.occupations = occupations;
15     }
16
17     public static BuilderExampleBuilder builder() {
18         return new BuilderExampleBuilder();
19     }
20
21     public static class BuilderExampleBuilder {
22         private String name;
23         private int age;
24         private java.util.ArrayList<String> occupations;
25
26         BuilderExampleBuilder() {
27         }
28
29         public BuilderExampleBuilder name(String name) {
30             this.name = name;
31             return this;
32         }
33
34         public BuilderExampleBuilder age(int age) {
35             this.age = age;
36             return this;
37         }
38
39         public BuilderExampleBuilder occupation(String occupation) {
40             if (this.occupations == null) {
41                 this.occupations = new java.util.ArrayList<String>();
42             }
43
44             this.occupations.add(occupation);
45             return this;
46         }
47
48         public BuilderExampleBuilder occupations(Collection<? extends String> occupations) {
49             if (this.occupations == null) {
50                 this.occupations = new java.util.ArrayList<String>();
51             }
52
53             this.occupations.addAll(occupations);
54             return this;
55         }
56
57         public BuilderExampleBuilder clearOccupations() {
58             if (this.occupations != null) {
59                 this.occupations.clear();
60             }
61
62             return this;
63         }
64
65         public BuilderExample build() {
66             //complicated switch statement to produce a compact properly sized immutable set omitted
67             // go to https://projectlombok.org/features/Singular-snippet.html to see it.
68             Set<String> occupations = ...;
69             return new BuilderExample(name, age, occupations);
70         }
71
72         @java.lang.Override
73         public String toString() {
74             return "BuilderExample.BuilderExampleBuilder(name = " + this.name + ", age = "
75                     + this.age + ", occupations = " + this.occupations + ")";
76         }
77     }
78 }

（3）下面是一个简单的测试样例：

1 BuilderExample be = BuilderExample.builder()
2         .name("hangge")
3         .age(123)
4         .occupation("ABC")
5         .occupation("DEF")
6         .build();
7
8 return be.toString();

14，@SneakyThrows

（1）该注解用在方法上，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。

（2）也可以使用 @SneakyThrows(Exception.class) 的形式指定抛出哪种异常。

 1 // 使用注解
 2 public class SneakyThrows implements Runnable {
 3     @SneakyThrows(UnsupportedEncodingException.class)
 4     public String utf8ToString(byte[] bytes) {
 5         return new String(bytes, "UTF-8");
 6     }
 7
 8     @SneakyThrows
 9     public void run() {
10         throw new Throwable();
11     }
12 }
13
14 // 不使用注解
15 public class SneakyThrows implements Runnable {
16     public String utf8ToString(byte[] bytes) {
17         try{
18             return new String(bytes, "UTF-8");
19         }catch(UnsupportedEncodingException uee){
20             throw Lombok.sneakyThrow(uee);
21         }
22     }
23
24     public void run() {
25         try{
26             throw new Throwable();
27         }catch(Throwable t){
28             throw Lombok.sneakyThrow(t);
29         }
30     }
31 }

15，@Synchronized

该注解用在类方法或者实例方法上，效果和 synchronized 关键字相同，区别在于锁对象不同。对于类方法和实例方法，它俩区别在于：

• synchronized 关键字的锁对象分别是“类的 class 对象”和“this 对象”
• @Synchronized 的锁对象分别是“私有静态 final 对象 lock”和“私有 final 对象 lock”。当然，也可以自己指定锁对象。

 1 // 使用注解
 2 public class Synchronized {
 3     private final Object readLock = new Object();
 4
 5     @Synchronized
 6     public static void hello() {
 7         System.out.println("world");
 8     }
 9
10     @Synchronized
11     public int answerToLife() {
12         return 42;
13     }
14
15     @Synchronized("readLock")
16     public void foo() {
17         System.out.println("bar");
18     }
19 }
20
21 // 不使用注解
22 public class Synchronized {
23     private static final Object $LOCK = new Object[0];
24     private final Object $lock = new Object[0];
25     private final Object readLock = new Object();
26
27     public static void hello() {
28         synchronized($LOCK) {
29             System.out.println("world");
30         }
31     }
32
33     public int answerToLife() {
34         synchronized($lock) {
35             return 42;
36         }
37     }
38
39     public void foo() {
40         synchronized(readLock) {
41             System.out.println("bar");
42         }
43     }
44 }