10:45:54.742 [main] ERROR org.springframework.boot.SpringApplication - Application run failed java.lang.NoSuchMethodError: org.yaml.snakeyaml.nodes.ScalarNode.getScalarStyle()Lorg/yaml/snakeyaml/DumperOptions$ScalarStyle; at org.springframework.boot.env.OriginTrackedYamlLoader$KeyScalarNode.<init>(OriginTrackedYamlLoader.java:127) at org.springframework.boot.env.OriginTrackedYamlLoader$KeyScalarNode.get(OriginTrackedYamlLoader.java:138) at org.springframework.boot.env.OriginTrackedYamlLoader$KeyScalarNode.get(OriginTrackedYamlLoader.java:133) at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1384) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566) at org.springframework.boot.env.OriginTrackedYamlLoader$OriginTrackingConstructor.replaceMappingNodeKeys(OriginTrackedYamlLoader.java:99) at org.springframework.boot.env.OriginTrackedYamlLoader$OriginTrackingConstructor.constructObject(OriginTrackedYamlLoader.java:92) at org.yaml.snakeyaml.constructor.BaseConstructor.constructDocument(BaseConstructor.java:161) at org.yaml.snakeyaml.constructor.BaseConstructor.getData(BaseConstructor.java:127) at org.yaml.snakeyaml.Yaml$1.next(Yaml.java:547) at org.springframework.beans.factory.config.YamlProcessor.process(YamlProcessor.java:160) at org.springframework.beans.factory.config.YamlProcessor.process(YamlProcessor.java:134) at org.springframework.boot.env.OriginTrackedYamlLoader.load(OriginTrackedYamlLoader.java:75) at org.springframework.boot.env.YamlPropertySourceLoader.load(YamlPropertySourceLoader.java:50) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.loadDocuments(ConfigFileApplicationListener.java:574) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.load(ConfigFileApplicationListener.java:528) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.loadForFileExtension(ConfigFileApplicationListener.java:502) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.load(ConfigFileApplicationListener.java:469) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.lambda$null$6(ConfigFileApplicationListener.java:450) at java.lang.Iterable.forEach(Iterable.java:75) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.lambda$load$7(ConfigFileApplicationListener.java:449) at java.lang.Iterable.forEach(Iterable.java:75) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.load(ConfigFileApplicationListener.java:446) at org.springframework.boot.context.config.ConfigFileApplicationListener$Loader.load(ConfigFileApplicationListener.java:334) at org.springframework.boot.context.config.ConfigFileApplicationListener.addPropertySources(ConfigFileApplicationListener.java:209) at org.springframework.boot.context.config.ConfigFileApplicationListener.postProcessEnvironment(ConfigFileApplicationListener.java:192) at org.springframework.boot.context.config.ConfigFileApplicationListener.onApplicationEnvironmentPreparedEvent(ConfigFileApplicationListener.java:179) at org.springframework.boot.context.config.ConfigFileApplicationListener.onApplicationEvent(ConfigFileApplicationListener.java:165) at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127) at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:75) at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:54) at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:347) at org.springframework.boot.SpringApplication.run(SpringApplication.java:306) at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248)
核对了下引入的包，发现项目中额外引入了1.19版本的org.yaml.snakeyaml包，这个包里确实没有这个方法。把这个包改成1.26的即可。
原代码：
username:root password:123456
项目启动报以下异常：
Caused by: org.yaml.snakeyaml.scanner.ScannerException: while scanning a simple key
产生问题的根源：application.yml文件键、值对之间要用冒号：隔开，而且冒号和值之间有一个空格
上述异常产生的就是键后面的：号紧接着写值，没有留一个空格。
冒号：后面留出一个空格后再写值
原代码参见下图：
项目启动以后报以下异常：
Caused by: org.yaml.snakeyaml.scanner.ScannerException: mapping values are not allowed here
或
Caused by: org.yaml.snakeyaml.parser.ParserException: while parsing a block mapping
expected <block end>, but found '<block mapping start>'
in 'reader', line 11, column 3:
jpa:
产生问题的根源：application.yml一级键，空一格写就可以了。像Jpa这样是一级键，下属的database是二级键。
Jpa向左前进一格到中间箭头的方位即可。
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。
