SpringBoot - Lombok使用详解5(@log、@Buinder、@SneakyThrows、@Synchronized)
作者: hangge 发布时间: 2019-10-10 浏览: 2248 次 编辑七、Lombok注解详解(4)
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。
@CommonsLog private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog(LogExample.class); @JBossLog private static final org.jboss.logging.Logger log = org.jboss.logging.Logger.getLogger(LogExample.class); @Log private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName()); @Log4j private static final org.apache.log4j.Logger log = org.apache.log4j.Logger.getLogger(LogExample.class); @Log4j2 private static final org.apache.logging.log4j.Logger log = org.apache.logging.log4j.LogManager.getLogger(LogExample.class); @Slf4j private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class); @XSlf4j private static final org.slf4j.ext.XLogger log = org.slf4j.ext.XLoggerFactory.getXLogger(LogExample.class);(2)下面是一个简单的使用样例:
// 使用注解 @Log public class LogExample { public static void main(String... args) { log.error("Something's wrong here"); } } // 不使用注解 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.error("Something's wrong here"); } }
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。
package com.example.demo; import lombok.Builder; import lombok.Singular; import java.util.Set; @Builder public class BuilderExample { private String name; private int age; @Singular private Set<String> occupations; }
(2)上面相当于如下传统的 Java 代码:
package com.example.demo; import java.util.Collection; import java.util.Set; public class BuilderExample { private String name; private int age; private Set<String> occupations; BuilderExample(String name, int age, Set<String> occupations) { this.name = name; this.age = age; this.occupations = occupations; } public static BuilderExampleBuilder builder() { return new BuilderExampleBuilder(); } public static class BuilderExampleBuilder { private String name; private int age; private java.util.ArrayList<String> occupations; BuilderExampleBuilder() { } public BuilderExampleBuilder name(String name) { this.name = name; return this; } public BuilderExampleBuilder age(int age) { this.age = age; return this; } public BuilderExampleBuilder occupation(String occupation) { if (this.occupations == null) { this.occupations = new java.util.ArrayList<String>(); } this.occupations.add(occupation); return this; } public BuilderExampleBuilder occupations(Collection<? extends String> occupations) { if (this.occupations == null) { this.occupations = new java.util.ArrayList<String>(); } this.occupations.addAll(occupations); return this; } public BuilderExampleBuilder clearOccupations() { if (this.occupations != null) { this.occupations.clear(); } return this; } public BuilderExample build() { //complicated switch statement to produce a compact properly sized immutable set omitted // go to https://projectlombok.org/features/Singular-snippet.html to see it. Set<String> occupations = ...; return new BuilderExample(name, age, occupations); } @java.lang.Override public String toString() { return "BuilderExample.BuilderExampleBuilder(name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")"; } } }
(3)下面是一个简单的测试样例:
BuilderExample be = BuilderExample.builder() .name("hangge") .age(123) .occupation("ABC") .occupation("DEF") .build(); 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。
// 使用注解 public class SneakyThrows implements Runnable { @SneakyThrows(UnsupportedEncodingException.class) public String utf8ToString(byte[] bytes) { return new String(bytes, "UTF-8"); } @SneakyThrows public void run() { throw new Throwable(); } } // 不使用注解 public class SneakyThrows implements Runnable { public String utf8ToString(byte[] bytes) { try{ return new String(bytes, "UTF-8"); }catch(UnsupportedEncodingException uee){ throw Lombok.sneakyThrow(uee); } } public void run() { try{ throw new Throwable(); }catch(Throwable t){ throw Lombok.sneakyThrow(t); } } }
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。
// 使用注解 public class Synchronized { 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"); } } // 不使用注解 public class Synchronized { 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"); } } }