官网地址: https://projectlombok.org
官网的首页视频演示在eclipse中如何使用Lombok;
Project Lombok is a java library that automatically plugs into your editor and build tools, spicing up your java.
Never write another getter or equals method again, with one annotation your class has a fully featured builder, Automate your logging variables, and much more.
翻译:
Lombok项目是一个java的库,可以自动的通过插件的方式安装到你的编辑器和构建工具中,给你的Java代码调味,再也不用写 getter和equals方法了,通过一个类上的注解你拥有了建造者的特征,自动的声明了一个日志变量,还有更多功能;
自由使用final本地变量;
从0.10版本开始引入
你可以使用val作为本地变量的申明,来替代写它的实际类型。如果你这样做了,类型将会从初始化表达式中被推断,本地变量也会被设置为final,这个特征工作在如下场景:
1.本地变量;
2.foreach循环;
在类的成员中并不会生效,初始化表达式是需要的。
val实际上是一个类型的排序,作为一个真实的类存在于lombok的包中,你必须引入val才能工作(或者使用lombok.val作为类型),在本地变量声明中这种类型的存在会触发两个操作:
1.增加final关键字;
2.复制初始化表达式的类型,用来重写这个伪造的val类型;
注意这个功能在netbeans中不会起作用;
注意事项:
对于混合的类型,会推断得到公共的父类,而不是共享的接口。
实例代码:不适用lombok;
package com.springpractice._val; import java.util.ArrayList; import java.util.HashMap; import java.util.Map; /** * Hello world! */ public class App { public String test1() { final ArrayList<String> exampleList = new ArrayList<>(); exampleList.add("hello world"); final String firstElement = exampleList.get(0); final String returnString = firstElement.toLowerCase(); System.out.println(returnString); return returnString; } public void test2() { final HashMap<Integer, String> map = new HashMap<>(); map.put(0, "zero"); map.put(5, "five"); for (final Map.Entry<Integer, String> entry : map.entrySet()) { System.out.printf("%d: %s /n", entry.getKey(), entry.getValue()); } } public static void main(String[] args) { final App app = new App(); app.test1(); System.out.println("======"); app.test2(); } }
使用lombok ;
package com.springpractice._val; import lombok.val; import java.util.ArrayList; import java.util.HashMap; /** * Hello world! */ public class AppLombok { //不能使用在类的成员变量上,会报编译错误 // val String name; public String test1() { val exampleList = new ArrayList<String>(); exampleList.add("hello world"); val firstElement = exampleList.get(0); final String returnString = firstElement.toLowerCase(); System.out.println(returnString); return returnString; } public void test2() { val map = new HashMap<Integer, String>(); map.put(0, "zero"); map.put(5, "five"); for (val entry : map.entrySet()) { System.out.printf("%d: %s /n", entry.getKey(), entry.getValue()); } } public static void main(String[] args) { final AppLombok app = new AppLombok(); app.test1(); System.out.println("======"); app.test2(); } }
替代本地变量;
package com.springpractice._var; import lombok.var; import java.awt.*; /** * 说明:var的使用 * @author carter * 创建时间: 2019年10月10日 20:08 **/ public class App { public static void main(String[] args) { var x = "Hello"; //编译报错,类型是String // x=1; var y = Color.RED; // y=x; //var的类型如果是object ,则不是它的使用场景 var z = new Object(); z = x; System.out.println(x); } }
自动检查,告别NPE的爱恨情仇。
不使用lombok;
package com.springpractice.nonnull; import lombok.NonNull; import java.util.Objects; /** * 说明:TODO * @author carter * 创建时间: 2019年10月10日 20:16 **/ public class App extends Something{ private String name; public App(Person person){ super("Hello"); if (Objects.isNull(person)){ throw new NullPointerException("person is marked @NonNull but is null"); } this.name = person.getName(); } public static void main(String[] args) { new App(null); } }
使用lombok;
package com.springpractice.nonnull; import lombok.NonNull; /** * 说明:TODO * @author carter * 创建时间: 2019年10月10日 20:20 **/ public class AppLombok extends Something { private String name; public AppLombok(@NonNull Person person){ super("Hello"); this.name = person.getName(); } public static void main(String[] args) { new AppLombok(null); } }
效果一样:
/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/lib/tools.jar:/Users/lifesense-szyf01/src/git/github/springbootpractice/lombok-demo/target/classes:/Users/lifesense-szyf01/.m2/repository/org/projectlombok/lombok/1.18.8/lombok-1.18.8.jar com.springpractice.nonnull.AppLombok Exception in thread "main" java.lang.NullPointerException: person is marked non-null but is null at com.springpractice.nonnull.AppLombok.<init>(AppLombok.java:15) at com.springpractice.nonnull.AppLombok.main(AppLombok.java:21) Process finished with exit code 1
代码路径: git@github.com:carterbrother/springbootpractice.git/lombok-demo
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