乐趣区

lombok深入实践

jiezi

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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