lombok深入实践
官网视频
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；
特征列表
val
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。
在含糊的场景下：如果初始化为null,会推断得到Object.
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();
}
}
var
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);
}
}
NonNull
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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