spring boot: Whitelabel Error Page的解决方案

    初次使用spring boot，按照其官网Building a RESTful Web Service搭建运行一个demo，代码如下:
pom.xml

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<?xml version="1.0" encoding="UTF-8"?>  
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  
    <modelVersion>4.0.0</modelVersion>  
      
    <groupId>personal.timeless</groupId>  
    <artifactId>CommentSystem</artifactId>  
    <packaging>war</packaging>  
    <version>0.0.1-SNAPSHOT</version>  
      
    <name>CommentSystem Maven Webapp</name>  
    <url>http://maven.apache.org</url>  
      
    <parent>  
        <groupId>org.springframework.boot</groupId>  
        <artifactId>spring-boot-starter-parent</artifactId>  
        <version>1.4.2.RELEASE</version>  
    </parent>  
  
    <dependencies>  
        <dependency>  
            <groupId>org.springframework.boot</groupId>  
            <artifactId>spring-boot-starter-web</artifactId>  
        </dependency>  
        <dependency>  
            <groupId>org.springframework.boot</groupId>  
            <artifactId>spring-boot-starter-test</artifactId>  
            <scope>test</scope>  
        </dependency>  
        <dependency>  
            <groupId>com.jayway.jsonpath</groupId>  
            <artifactId>json-path</artifactId>  
            <scope>test</scope>  
        </dependency>  
    </dependencies>  
  
    <properties>  
        <java.version>1.8</java.version>  
    </properties>  
  
  
    <build>  
        <plugins>  
            <plugin>  
                <groupId>org.springframework.boot</groupId>  
                <artifactId>spring-boot-maven-plugin</artifactId>  
            </plugin>  
        </plugins>  
    </build>  
  
    <repositories>  
        <repository>  
            <id>spring-releases</id>  
            <url>https://repo.spring.io/libs-release</url>  
        </repository>  
    </repositories>  
    <pluginRepositories>  
        <pluginRepository>  
            <id>spring-releases</id>  
            <url>https://repo.spring.io/libs-release</url>  
        </pluginRepository>  
    </pluginRepositories>  
</project>  

controller Comment.java

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import org.springframework.web.bind.annotation.RequestMapping;  
import org.springframework.web.bind.annotation.RequestParam;  
import org.springframework.web.bind.annotation.RestController;  
  
@RestController  
public class Comments {  
      
    @RequestMapping("/greeting")  
    public String greeting(@RequestParam(value="name", defaultValue="World") String name) {  
        return name;  
    }  
}  

主文件 App.java

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import org.springframework.boot.SpringApplication;  
import org.springframework.boot.autoconfigure.SpringBootApplication;  
  
@SpringBootApplication  
public class App  
{  
    public static void main(String[] args) throws Exception {  
        SpringApplication.run(App.class, args);  
    }  
}  

运行起来没报错，但是打开浏览器输入地址http://localhost:8080/greeting出现以下页面



检查地址没问题，核对jar包也正确。google,有说少jar包，按照回答添加以后也无济于事。折腾了一会找到了原因



竟然时目录文件结构问题，最后附上官网说明http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#using-boot-structuring-your-code

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14.2 Locating the main application class  
We generally recommend that you locate your main application class in a root package above other classes. The @EnableAutoConfiguration annotation is often placed on your main class, and it implicitly defines a base “search package” for certain items. For example, if you are writing a JPA application, the package of the @EnableAutoConfiguration annotated class will be used to search for @Entity items.  
  
Using a root package also allows the @ComponentScan annotation to be used without needing to specify a basePackage attribute. You can also use the @SpringBootApplication annotation if your main class is in the root package.  
  
Here is a typical layout:  
  
com  
 +- example  
     +- myproject  
         +- Application.java  
         |  
         +- domain  
         |   +- Customer.java  
         |   +- CustomerRepository.java  
         |  
         +- service  
         |   +- CustomerService.java  
         |  
         +- web  
             +- CustomerController.java