Spring Boot从配置获取随机值
须弥零一
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2021-04-02 16:00
Spring Boot从配置获取随机值
application.properties 或 application.yml）中设置一个随机值，应该怎么办呢？这个Spring Boot已经有了解决方案。下面就通过示例详细说明。通过配置获取随机值
•application.properties
my.id=${random.uuid}my.secret="${random.value}"my.number="${random.int}"my.bignumber="${random.long}"my.uuid="${random.uuid}"my.number-less-than-ten="${random.int(10)}"my.number-in-range="${random.int[1024,65536]}"
•application.yml
my:id: ${random.uuid}secret: "${random.value}"number: "${random.int}"bignumber: "${random.long}"uuid: "${random.uuid}"number-less-than-ten: "${random.int(10)}"number-in-range: "${random.int[1024,65536]}"
import org.springframework.beans.factory.annotation.Autowired;import org.springframework.beans.factory.annotation.Value;import org.springframework.core.env.Environment;import org.springframework.stereotype.Component;@Componentpublic class RandomValuesTester {@Value("${my.id}")private String id;@Value("${my.secret}")private String secret;@Value("${my.number}")private String number;@Value("${my.bignumber}")private String bigNumber;@Value("${my.uuid}")private String uuid;@Value("${my.number-less-than-ten}")private String numberLessThanTen;@Value("${my.number-in-range}")private String numberInRange;@Autowiredprivate Environment environment;public void test() {placeholderTest();System.out.println("========================");useEnvironmentTest();}private void placeholderTest() {System.out.println(id);System.out.println(secret);System.out.println(number);System.out.println(bigNumber);System.out.println(uuid);System.out.println(numberLessThanTen);System.out.println(numberInRange);}private void useEnvironmentTest() {System.out.println(environment.getProperty("my.id"));System.out.println(environment.getProperty("my.secret"));System.out.println(environment.getProperty("my.number"));System.out.println(environment.getProperty("my.bignumber"));System.out.println(environment.getProperty("my.uuid"));System.out.println(environment.getProperty("my.number-less-than-ten"));System.out.println(environment.getProperty("my.number-in-range"));}}
2021-03-31 19:45:57.632 INFO 25308 --- [ main] com.jeremy.tech.lab.LabApplication : Started LabApplication in 2.034 seconds (JVM running for 3.125)43adc303-aa7b-4424-ac59-4261b75274614032da51f1edd76256abee1683c6ca96-354560558-632597375314852670004e686db-4a1a-42af-8d59-1d17501166ae835928========================258a9bb9-f6fc-4d5b-bcea-8a4528a60c6d04e44548ea9a5c5b2c0bee1a4f2c1658-722507177-313282001081326805509dba0b-caf2-4477-8970-de648baa388e8511412021-03-31 19:45:58.158 INFO 25308 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Shutting down ExecutorService 'applicationTaskExecutor'
environment.getProperty("xxx")）看看是不是每次都是随机的值。下面介绍一下这些值是怎么获取的。源码分析
org.springframework.boot.env.RandomValuePropertySource 这个类来实现。这个类的源码如下（关键部分）：
public class RandomValuePropertySource extends PropertySource<Random> {/*** Name of the random {@link PropertySource}.*/public static final String RANDOM_PROPERTY_SOURCE_NAME = "random";private static final String PREFIX = "random.";public RandomValuePropertySource(String name) {super(name, new Random());}@Overridepublic Object getProperty(String name) {if (!name.startsWith(PREFIX)) {return null;}logger.trace(LogMessage.format("Generating random property for '%s'", name));return getRandomValue(name.substring(PREFIX.length()));}private Object getRandomValue(String type) {if (type.equals("int")) {return getSource().nextInt();}if (type.equals("long")) {return getSource().nextLong();}String range = getRange(type, "int");if (range != null) {return getNextIntInRange(range);}range = getRange(type, "long");if (range != null) {return getNextLongInRange(range);}if (type.equals("uuid")) {return UUID.randomUUID().toString();}return getRandomBytes();}private String getRange(String type, String prefix) {if (type.startsWith(prefix)) {int startIndex = prefix.length() + 1;if (type.length() > startIndex) {return type.substring(startIndex, type.length() - 1);}}return null;}private int getNextIntInRange(String range) {String[] tokens = StringUtils.commaDelimitedListToStringArray(range);int start = Integer.parseInt(tokens[0]);if (tokens.length == 1) {return getSource().nextInt(start);}return start + getSource().nextInt(Integer.parseInt(tokens[1]) - start);}private long getNextLongInRange(String range) {String[] tokens = StringUtils.commaDelimitedListToStringArray(range);if (tokens.length == 1) {return Math.abs(getSource().nextLong() % Long.parseLong(tokens[0]));}long lowerBound = Long.parseLong(tokens[0]);long upperBound = Long.parseLong(tokens[1]) - lowerBound;return lowerBound + Math.abs(getSource().nextLong() % upperBound);}private Object getRandomBytes() {byte[] bytes = new byte[32];getSource().nextBytes(bytes);return DigestUtils.md5DigestAsHex(bytes);}}
分析
Object getProperty(String name) 这个函数来获取的，这个函数是继承了父类的重写方法。Object getRandomValue(String type) 可以很清楚的看到每种随机值的获取方式。源码很简单我就不展开说明了。private Object getRandomValue(String type) {if (type.equals("int")) {return getSource().nextInt();}if (type.equals("long")) {return getSource().nextLong();}String range = getRange(type, "int");if (range != null) {return getNextIntInRange(range);}range = getRange(type, "long");if (range != null) {return getNextLongInRange(range);}if (type.equals("uuid")) {return UUID.randomUUID().toString();}return getRandomBytes();}
结论
通过分析我们可以得出结论：
•${random.value} 的值是一个随机的32位十六进制的MD5摘要值•${random.int} 的值是通过 new Random() 获取的一个随机的int值•${random.long}的值是通过 new Random() 获取的一个随机的long值•${random.uuid} 的值是通过 UUID.randomUUID().toString() 获取的一个随机UUID值•${random.int(10)} 的值是一个不大于10的int值•${random.int[1024,65536]} 的值是一个包含1024，不包含65535的一个随机值
注：${random.int[min,max]} 中的 [min, max] 是一个包含min不包含max的范围，{random.long[min,max]} 也是一样的，只不过最大值是Long.MAX 而已。
最后
PropertySource 入手，属性的初始化在 Application.run 函数中的如下三个关键函数调用中赋值：•prepareContext•refreshContext•afterRefresh
*.properties 和 *.yml 。如果您的项目中同时存在这两个配置文件，并且配置文件中的属性有同样的key，最终 *.yml 中的配置会覆盖 *.properties 中的配置。欢迎关注我的公众号“须弥零一”，原创技术文章第一时间推送。
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