Project build error: Non-resolvable parent POM for com.example:demo-1:0.0.1-SNAPSHOT: Failure to transfer org.springframework.boot:spring-boot-starter-parent:pom:1.5.2.RELEASE from https://repo.maven.apache.org/maven2 was cached in the local repository, resolution will not be reattempted until the update interval of central has elapsed or updates are forced. Original error: Could not transfer artifact org.springframework.boot:spring-boot-starter-parent:pom:1.5.2.RELEASE from/to central (

解決方法：
參考stack overflow：
I‘ve also encountered a lot of error when creating a new STS project 
for the first time. This seems to be happen only if I don‘t have any 
Maven repository or haven‘t launch/use Maven before. In my case, 
I solve this by launching Maven command from command line manually. 
Try to ‘cd‘ to the project directory that contains pom.xml and call
 
 
mvn that comes with STS from there.

sql
cd c:\users\name\sts-projects\projectname
c:\programs\springsource\apache-maven-3.0.3\bin\mvn compile

Then, open STS, right click on project name, select ‘Maven‘, ‘Update Project…‘ Select on ‘Force Update of Snapshots/Releases‘. Don‘t select ‘Offline‘.
翻譯過來就是：開啟終端，進入專案的根目錄，然後使用 maven bin 目錄下的 mvn 編譯命令編譯一下（也就是mvn compile），完成之後右鍵專案 選擇Maven，之後選擇Update Project 即可。（個人理解就是清空專案的jar包倉庫，之後更新重新下載）
原文：