Lombok安装及Spring Boot集成Lombok

文章目录

• Lombok有什么用
• 使用Lombok时需要注意的点
• Lombok的安装
• spring boot集成Lombok
• Lombok常用注解
• @NonNull
• @Cleanup
• @Getter/@Setter
• @Getter(lazy=true)
• @ToString/@EqualsAndHashCode
• @NoArgsConstructor/@RequiredArgsConstructor /@AllArgsConstructor
• @Data/@Value
• @SneakyThrows
• @Synchronized
• @Log
• 参考资料

Lombok有什么用

在我们实体Bean中有大量的Getter/Setter方法以及toString, hashCode等可能不会用到，但是某些时候仍然需要复写；在使用Lombok之后，将由其来自动帮你实现代码生成。注意，其是在编译源码过程中，帮你自动生成的。就是说，将极大减少你的代码总量。

Lombok的官方地址： https://projectlombok.org/

使用Lombok时需要注意的点

• 在类需要序列化、反序列化时或者需要详细控制字段时，应该谨慎考虑是否要使用Lombok，因为在这种情况下容易出问题。例如：Jackson、Json序列化
• 使用Lombok虽然能够省去手动创建setter和getter方法等繁琐事情，但是却降低了源代码文件的可读性和完整性，减低了阅读源代码的舒适度
• 使用@Slf4j还是@Log4j注解，需要根据实际项目中使用的日志框架来选择。
• Lombok并非处处适用，我们需要选择适合的地方使用Lombok，例如pojo是一个好地方，因为pojo很单纯

Lombok的安装

eclipse安装Lombok步骤：

1. 下载最新的lombok.jar包，下载地址：https://projectlombok.org/download.html
2. 进入cmd窗口，切到Lombok下载的目录，运行命令： java -jar lombok.jar，会出现如下界面：
   已经默认选好了eclipse安装目录（这个可能是因为我只有一个盘，如果没有默认选择，可以自己点击下方Specify location...按钮选择eclipse安装目录），点击图中红色箭头指向的按钮，即可完成安装。成功界面如下：
3. eclipse安装目录下的eclipse.ini文件末尾已经加了一行内容（这个路径因人而异，和eclipse安装目录有关），如下：
   而且安装目录下也多了一个lombok.jar

spring boot集成Lombok

1. 先去http://start.spring.io/在线生成一个spring boot项目脚手架，导入eclipse。

2. 在pom.xml里添加Lombok依赖：

   <dependency>
       <groupId>org.projectlombok</groupId>
       <artifactId>lombok</artifactId>
       <version>1.16.14</version>
   </dependency>
   

3. 在src/main/java/com/example/springbootlombok/entity下新建一个student.java的Java bean：

   package com.example.springbootlombok.entity;
   import lombok.Data;
   @Data
   
   public class Student {
   
   private String name;
   
   private int age;
   
   }
   

4. 在src/test/java/com/example/springbootlombok下新建一个TestEntity.java的测试类：

   package com.example.springbootlombok;
   import org.junit.Test;
   
   import org.junit.runner.RunWith;
   
   import org.springframework.boot.test.context.SpringBootTest;
   
   import org.springframework.test.context.junit4.SpringRunner;
   import com.example.springbootlombok.entity.Student;
   import lombok.extern.slf4j.Slf4j;
   @RunWith(SpringRunner.class)
   
   @SpringBootTest
   
   @Slf4j
   
   public class TestEntity {
   Student student <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Student</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
   	
   <span class="token annotation punctuation">@Test</span>
   <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
   	student<span class="token punctuation">.</span><span class="token function">setName</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
   	student<span class="token punctuation">.</span><span class="token function">setAge</span><span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
   	log<span class="token punctuation">.</span><span class="token function">info</span><span class="token punctuation">(</span><span class="token string">"测试结果:"</span> <span class="token operator">+</span> student<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
   
   }
   

5. 执行JUnit测试，成功的话，日志里会有打印测试结果:Student(name=张三, age=12)，至此，spring boot已经成功集成Lombok了。

Lombok常用注解

@NonNull

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：

编译前的代码：

//成员方法参数加上@NonNull注解
public String getName(@NonNull Person p) {
    return p.getName();
}

编译后的代码：

public String getName(@NonNull Person p) {
    if (p == null) {
        throw new NullPointerException("person");
    }
    return p.getName();
}

@Cleanup

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：

编译前的代码：

public static void main(String[] args) throws IOException {
    @Cleanup InputStream in = new FileInputStream(args[0]);
    @Cleanup OutputStream out = new FileOutputStream(args[1]);
    byte[] b = new byte[1024];
    while (true) {
        int r = in.read(b);
        if (r == -1) break;
        out.write(b, 0, r);
    }
 }

编译后的代码：

public static void main(String[] args) throws IOException {
    InputStream in = new FileInputStream(args[0]);
    try {
        OutputStream out = new FileOutputStream(args[1]);
        try {
            byte[] b = new byte[10000];
            while (true) {
                int r = in.read(b);
                if (r == -1) break;
                out.write(b, 0, r);
            }
        } finally {
            if (out != null) {
                out.close();
            }
        }
    } finally {
        if (in != null) {
            in.close();
        }
    }
}

@Getter/@Setter

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：

编译前的代码：

public class Programmer {
    @Getter
    @Setter
    private String name;
<span class="token annotation punctuation">@Setter</span><span class="token punctuation">(</span>AccessLevel<span class="token punctuation">.</span>PROTECTED<span class="token punctuation">)</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>

<span class="token annotation punctuation">@Getter</span><span class="token punctuation">(</span>AccessLevel<span class="token punctuation">.</span>PUBLIC<span class="token punctuation">)</span>
<span class="token keyword">private</span> String language<span class="token punctuation">;</span>

}

编译后的代码：

public class Programmer {
    private String name;
    private int age;
    private String language;
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setName</span><span class="token punctuation">(</span>String name<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> String <span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> name<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">protected</span> <span class="token keyword">void</span> <span class="token function">setAge</span><span class="token punctuation">(</span><span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> String <span class="token function">getLanguage</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> language<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

这两个注解还可以直接用在类上，可以为此类里的所有非静态成员变量生成对应的get和set方法。

@Getter(lazy=true)

如果Bean的一个字段的初始化是代价比较高的操作，比如加载大量的数据；同时这个字段并不是必定使用的。那么使用懒加载机制，可以保证节省资源。

懒加载机制，是对象初始化时，该字段并不会真正的初始化，而是第一次访问该字段时才进行初始化字段的操作。

@ToString/@EqualsAndHashCode

这两个注解也比较好理解，就是生成toString，equals和hashcode方法，同时后者还会生成一个canEqual方法，用于判断某个对象是否是当前类的实例，生成方法时只会使用类中的非静态和非transient成员变量，这些都比较好理解，就不举例子了。

当然，这两个注解也可以添加限制条件，例如用@ToString(exclude={"param1","param2"})来排除param1和param2两个成员变量，或者用@ToString(of={"param1","param2"})来指定使用param1和param2两个成员变量，@EqualsAndHashCode注解也有同样的用法。

@NoArgsConstructor/@RequiredArgsConstructor /@AllArgsConstructor

这三个注解都是用在类上的，第一个和第三个都很好理解，就是为该类产生无参的构造方法和包含所有参数的构造方法，第二个注解则使用类中所有带有@NonNull注解的或者带有final修饰的成员变量生成对应的构造方法。当然，和前面几个注解一样，成员变量都是非静态的，另外，如果类中含有final修饰的成员变量，是无法使用@NoArgsConstructor注解的。

三个注解都可以指定生成的构造方法的访问权限，同时，第二个注解还可以用@RequiredArgsConstructor(staticName="methodName")的形式生成一个指定名称的静态方法，返回一个调用相应的构造方法产生的对象，下面来看一个生动鲜活的例子：

编译前的代码：

@RequiredArgsConstructor(staticName = "sunsfan")
@AllArgsConstructor(access = AccessLevel.PROTECTED)
@NoArgsConstructor
public class Shape {
    private int x;
    @NonNull
    private double y;
    @NonNull
    private String name;
}

编译后的代码：

public class Shape {
    private int x;
    private double y;
    private String name;
<span class="token keyword">public</span> <span class="token function">Shape</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token punctuation">}</span>

<span class="token keyword">protected</span> <span class="token function">Shape</span><span class="token punctuation">(</span><span class="token keyword">int</span> x<span class="token punctuation">,</span> <span class="token keyword">double</span> y<span class="token punctuation">,</span> String name<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>x <span class="token operator">=</span> x<span class="token punctuation">;</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>y <span class="token operator">=</span> y<span class="token punctuation">;</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token function">Shape</span><span class="token punctuation">(</span><span class="token keyword">double</span> y<span class="token punctuation">,</span> String name<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>y <span class="token operator">=</span> y<span class="token punctuation">;</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> Shape <span class="token function">sunsfan</span><span class="token punctuation">(</span><span class="token keyword">double</span> y<span class="token punctuation">,</span> String name<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">Shape</span><span class="token punctuation">(</span>y<span class="token punctuation">,</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

@Data/@Value

@Data注解综合了@Getter/@Setter，@ToString，@EqualsAndHashCode和@RequiredArgsConstructor注解，其中@RequiredArgsConstructor使用了类中的带有@NonNull注解的或者final修饰的成员变量，它可以使用@Data(staticConstructor="methodName")来生成一个静态方法，返回一个调用相应的构造方法产生的对象。

@Value注解和@Data类似，区别在于它会把所有成员变量默认定义为private final修饰，并且不会生成set方法。

@SneakyThrows

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：

编译前的代码：

public class SneakyThrows implements Runnable {
    @SneakyThrows(UnsupportedEncodingException.class)
    public String utf8ToString(byte[] bytes) {
        return new String(bytes, "UTF-8");
    }
<span class="token annotation punctuation">@SneakyThrows</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">Throwable</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

编译后的代码：

public class SneakyThrows implements Runnable {
    @SneakyThrows(UnsupportedEncodingException.class)
    public String utf8ToString(byte[] bytes) {
        try {
            return new String(bytes, "UTF-8");
        } catch(UnsupportedEncodingException uee) {
            throw Lombok.sneakyThrow(uee);
        }
    }
<span class="token annotation punctuation">@SneakyThrows</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">try</span> <span class="token punctuation">{</span>
        <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">Throwable</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">catch</span><span class="token punctuation">(</span>Throwable t<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">throw</span> Lombok<span class="token punctuation">.</span><span class="token function">sneakyThrow</span><span class="token punctuation">(</span>t<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

}

@Synchronized

这个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，synchronized关键字的锁对象分别是类的class对象和this对象，而@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，例子也很简单，往下看：

编译前的代码：

public class Synchronized {
    private final Object readLock = new Object();
<span class="token annotation punctuation">@Synchronized</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">hello</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"world"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token annotation punctuation">@Synchronized</span>
<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">answerToLife</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token number">42</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token annotation punctuation">@Synchronized</span><span class="token punctuation">(</span><span class="token string">"readLock"</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"bar"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

编译后的代码：

public class Synchronized {
    private static final Object $LOCK = new Object[0];
    private final Object $lock = new Object[0];
    private final Object readLock = new Object();
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">hello</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">synchronized</span><span class="token punctuation">(</span>$LOCK<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"world"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">answerToLife</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">synchronized</span><span class="token punctuation">(</span>$lock<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token number">42</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">synchronized</span><span class="token punctuation">(</span>readLock<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"bar"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

}

@Log

这个注解用在类上，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，同时，可以在注解中使用topic来指定生成log对象时的类名。不同的日志注解总结如下(上面是注解，下面是编译后的代码)：

@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);

参考资料

• Spring Boot下的lombok安装以及使用简介
• lombok注解介绍