ARTS 第46周

历史ARTS

Algorithm

package org.nocoder.leetcode.solution;

/**
 * AddBinary https://leetcode.com/problems/add-binary/
 * <p>
 * Given two binary strings a and b, return their sum as a binary string.
 * <p>
 * Example 1:
 * <p>
 * Input: a = "11", b = "1"
 * Output: "100"
 * Example 2:
 * <p>
 * Input: a = "1010", b = "1011"
 * Output: "10101"
 * Constraints:
 * <p>
 * 1 <= a.length, b.length <= 104
 * a and b consist only of '0' or '1' characters.
 * Each string does not contain leading zeros except for the zero itself.
 * Related Topics
 * Math
 * String
 * Bit Manipulation
 * Simulation
 *
 * @author yangjl
 * @description
 * @date 2023-05-19 15:31
 **/
public class AddBinary {
    public String addBinary(String a, String b) {
        if (a == null || b == null || a.length() > 10000 || b.length() > 10000)
            throw new RuntimeException("invalid parameters");

        // 两个字符串长度查，在短字符串前面补领0，方便计算
        int d = a.length() - b.length();
        String prefix = "";
        for (int i = 0; i < Math.abs(d); i++)
            prefix += "0";

        // 参数前面补0
        if (d > 0)
            b = prefix + b;
        else
            a = prefix + a;

        String[] aa = a.split("");
        String[] bb = b.split("");
        // 用字符串数组来存储结果，长度用aa和bb的都可以
        String[] res = new String[aa.length];

        // carry表示进位值
        String carry = "0";

        // 从末位开始相加
        for (int i = aa.length - 1; i >= 0; i--) {
            String sum = carry + aa[i] + bb[i];

            if ("000".equals(sum)) {
                res[i] = "0";
                carry = "0";
            }

            if ("001".equals(sum) || "010".equals(sum) || "100".equals(sum)) {
                res[i] = "1";
                carry = "0";
            }

            if ("101".equals(sum) || "110".equals(sum) || "011".equals(sum)) {
                res[i] = "0";
                carry = "1";
            }

            if ("111".equals(sum)) {
                res[i] = "1";
                carry = "1";
            }

            // 计算到数组首位时，依然有进位，需要变长数组，长度+1，首位赋值为1
            if (i == 0 && "1".equals(carry)) {
                // step1. 暂存res到temp
                String[] tem = res;
                // step2. 新建一个比原数组长度+1的数组
                res = new String[aa.length + 1];
                // step3. 首位赋值为1
                res[0] = "1";
                // step4. 把原数组内容复制过来，下标从1开始复制
                for (int i1 = 1; i1 < res.length; i1++)
                    res[i1] = tem[i1 - 1];
            }

        }

        String result = new String();
        for (int i = 0; i < res.length; i++)
            result += res[i];

        return result;
    }
}

Review

以前在完成Review这一项任务的时候，通过皓哥的专栏和引导，发现了很多优秀的国外技术网站，如medium、DZone、javatpoint、IBM Developer等等，阅读高质量的英文文章，可以提高英文水平，也可以学习大佬对技术理解的视角和思维方式。今天阅读的是dzone上一位大佬总结的java11到java17的新特性What’s New Between Java 11 and Java 17，篇幅不长，可以快速了解上一个LTS版本Java11到17的一些新特性。下面对文中提到的新特性作以下简要整理。

Text Blocks

文本块，类似python中的文本块支持换行。

public class TextBlock {
    public static void main(String[] args) {
        String json = """
                {
                    "name": "Jason",
                    "age": "34",
                    "mail": "yangjinlong86@gmail.com"
                }
                """;
        System.out.println(json);
    }
}

输出结果也是带格式的

{
    "name": "Jason",
    "age": "34",
    "mail": "yangjinlong86@gmail.com"
}

Switch Expressions

冒号改为箭头方式，不需要单独写break，代码更简洁

private static void withSwitchExpression(Fruit fruit) {
    switch (fruit) {
        case APPLE, PEAR -> System.out.println("Common fruit");
        case ORANGE, AVOCADO -> System.out.println("Exotic fruit");
        default -> System.out.println("Undefined fruit");
    }
}

支持返回值，如果一个case下需要多行代码，使用yield关键字指定返回值

private static void withYield(Fruit fruit) {
    String text = switch (fruit) {
        case APPLE, PEAR -> {
            System.out.println("the given fruit was: " + fruit);
            yield "Common fruit";
        }
        case ORANGE, AVOCADO -> "Exotic fruit";
        default -> "Undefined fruit";
    };
    System.out.println(text);
}

yield支持旧的 switch 语法，也不需要单独写break

private static void oldStyleWithYield(Fruit fruit) {
    System.out.println(switch (fruit) {
        case APPLE, PEAR:
            yield "Common fruit";
        case ORANGE, AVOCADO:
            yield "Exotic fruit";
        default:
            yield "Undefined fruit";
    });
}

Records

Records 用来创建一个不可变的数据类，与传统的类相比，无需我们再写构造器, getters, hashCode, equals 和 toString方法

使用new 创建Record时，如果参数与已经存在的Record相同，那么不会新建的Record副本与原Record是同一个实例。见以下代码最后一行的输出，hashcode是一样的。

private static void basicRecord() {
    record GrapeRecord(Color color, int nbrOfPits) {}
    GrapeRecord grape1 = new GrapeRecord(Color.BLUE, 1);
    GrapeRecord grape2 = new GrapeRecord(Color.WHITE, 2);
    System.out.println("Grape 1 is " + grape1);
    System.out.println("Grape 2 is " + grape2);
    System.out.println("Grape 1 equals grape 2? " + grape1.equals(grape2));
    GrapeRecord grape1Copy = new GrapeRecord(grape1.color(), grape1.nbrOfPits());
    System.out.println("Grape 1 equals its copy? " + grape1.equals(grape1Copy));
    System.out.println(grape1.hashCode() + " " + grape1Copy.hashCode());
}

Grape 1 is GrapeRecord[color=java.awt.Color[r=0,g=0,b=255], nbrOfPits=1]
Grape 2 is GrapeRecord[color=java.awt.Color[r=255,g=255,b=255], nbrOfPits=2]
Grape 1 equals grape 2? false
Grape 1 equals its copy? true
-520085790 -520085790

Record的构造方法中可以增加字段校验逻辑

    private static void basicRecordWithValidation() {
        record GrapeRecord(Color color, int nbrOfPits) {
            GrapeRecord {
                System.out.println("Parameter color=" + color + ", Field color=" + this.color());
                System.out.println("Parameter nbrOfPits=" + nbrOfPits + ", Field nbrOfPits=" + this.nbrOfPits());
                if (color == null) {
                    throw new IllegalArgumentException("Color may not be null");
                }
            }
        }
        GrapeRecord grape1 = new GrapeRecord(Color.BLUE, 1);
        System.out.println("Grape 1 is " + grape1);
        GrapeRecord grapeNull = new GrapeRecord(null, 2);
    }

Sealed Classes
- 使用关键字sealed配合permits来限定类的继承范围，不被允许的类继承该类会编译错误，提示'ClassName' is not allowed in the sealed hierarchy
- 继承了该类的子类需要声明自身的继承范围，使用关键字final、sealed和non-sealed来限定继承范围

Pattern matching for instanceof

instanceof的类名之后，跟一个变量名，可以省去强转和声明类的步骤

Object o = new GrapeClass(Color.BLUE, 2);
if (o instanceof GrapeClass grape) {
    System.out.println("This grape has " + grape.getNbrOfPits() + " pits.");
}

Helpful NullPointerExceptions
- 当发生空指针异常是，异常信息中直接会告诉你是哪个类的哪个方法导致的
```
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "com.mydeveloperplanet.myjava17planet.GrapeClass.getColor()" because the return value of "java.util.HashMap.get(Object)" is null
```
at com.mydeveloperplanet.myjava17planet.HelpfulNullPointerExceptions.main(HelpfulNullPointerExceptions.java:13)
Compact Number Formatting Support
- NumberFormat类中增加了format工厂方法，便于数字类型转换

Day Period Support Added

DateTimeFormatter 中新增了一个B模式，可以直接返回时间所属的时段信息

public class DayPeriod {
    public static void main(String[] args) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("B");
        System.out.println(dtf.format(LocalTime.of(8, 0)));
        System.out.println(dtf.format(LocalTime.of(13, 0)));
        System.out.println(dtf.format(LocalTime.of(20, 0)));
        System.out.println(dtf.format(LocalTime.of(23, 0)));
        System.out.println(dtf.format(LocalTime.of(0, 0)));
    }
}

上午
下午
晚上
晚上
午夜

默认返回值是当前时区，也可以指定Locale，例如：

dtf = DateTimeFormatter.ofPattern("B").withLocale(Locale.forLanguageTag("NL"));

Stream.toList()

旧版本中，如果要把Stream转换成List，需要调用collect(Collectors.toList)，Java 17 中，Stream增加了toList()方法，可以直接转换为List

private static void oldStyle() {
    Stream<String> stringStream = Stream.of("a", "b", "c");
    List<String> stringList =  stringStream.collect(Collectors.toList());
    for(String s : stringList) {
        System.out.println(s);
    }
}

private static void streamToList() {
    Stream<String> stringStream = Stream.of("a", "b", "c");
    List<String> stringList =  stringStream.toList();
    for(String s : stringList) {
        System.out.println(s);
    }
}

Tip

使用RabbitMQ时，如果设置了自动ack，再自行手动ack的话，会偶发性的导致消息丢失。

问题现象

A服务将数据通过MQ发送到B服务，期间出现消息丢失情况。

排查过程

1、A服务发送成功后记录了日志，消息是成功发送出去了。 2、B服务日志打印不规范，输出日志为null，经核实代码，推断message为空，导致RuntimeException。 3、查看RabbitMQ日志，发现异常信息如下：

2023-05-29 23:52:01.502 [error] <0.20990.12> Channel error on connection <0.2510.0> (10.42.0.1:42792 -> 10.42.0.5:5672, vhost: '/', user: 'admin'), channel 1150:
operation basic.ack caused a channel exception precondition_failed: unknown delivery tag 1

问题原因

到此问题基本明晰了，生产环境的配置文件没有将rabbitmq的ack设置为手动，默认值为none，是自动确认。代码中使用channel.basicAck()又进行了手动确认，这样的重复确认操作会导致偶发性消息丢失情况。

rabbitmq 为每一个channel维护了一个delivery tag的计数器，采用正向自增，新消息投递时自增，当消息响应时自减；在连续收发的场景中，由于消息发送的间隔较短，部分消息因 consumer的重复确认被rabbitmq 当做已处理而丢弃。

解决办法

取消自动确认，配置手动确认。

spring:
  rabbitmq:
    host: ${rabbitmqHost}
    port: ${rabbitmqPort}
    username: ${rabbitmqUsername}
    password: ${rabbitmqPassword}
    virtual-host: /
    listener:
      simple:
        retry:
          enabled: true
          max-attempts: 24
          initial-interval: 3600000
        acknowledge-mode: manual

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历史ARTS

Algorithm

Review

Tip

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