SpringBoot - Lombok使用详解5（@log、@Buinder、@SneakyThrows、@Synchronized）
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");
}
}
}Original url: Access
Created at: 2019-12-25 17:11:46
Category: default
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