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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