升級springboot2.x出現如下Elasticsearch相關錯誤：

NoNodeAvailableException[None of the configured nodes are available: [{#transport#-1}{729dgKKVSF-ti27v2_w68g}{10.0.2.23}{10.0.2.23:9300}]
]
	at org.elasticsearch.client.transport.TransportClientNodesService.ensureNodesAreAvailable(TransportClientNodesService.java:347)
	at org.elasticsearch.client.transport.TransportClientNodesService.execute(TransportClientNodesService.java:245)
	at org.elasticsearch.client.transport.TransportProxyClient.execute(TransportProxyClient.java:59)
	at org.elasticsearch.client.transport.TransportClient.doExecute(TransportClient.java:366)
	at org.elasticsearch.client.support.AbstractClient.execute(AbstractClient.java:408)
	at org.elasticsearch.action.ActionRequestBuilder.execute(ActionRequestBuilder.java:80)
	at org.elasticsearch.action.ActionRequestBuilder.execute(ActionRequestBuilder.java:54)
	at com.example.test.ExampleApplicationTests.search(ExampleApplicationTests.java:56)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:73)
	at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:83)
	at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
	at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
	at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
 

原因：springboot2.x最低支援elasticsearch5.x，而我之前的elasticsearch版本為2.4.6，所以在執行查詢時出現上述錯誤

解決方案：

1.將springBoot更改為1.5.x（例如：1.5.9），這樣就可以相容之前的elasticsearch2.x

2.如果springboot更改為2.x，那麼需要將elasticsearch升級為5.x（注意：升級elasticsearch為5.x後，你會發現存在相應的api也發生了變化）