spring boot遵循“约定优于配置”的原则，使用annotation对一些常规的配置项做默认配置，减少或不使用xml配置，让你的项目快速运行起来。spring boot的神奇不是借助代码的生成来实现的，而是通过条件注解来实现的。
自动配置AutoConfiguration是实现spring boot的重要原理，理解AutoConfiguration的运行原理特别重要，自己写一个AutoConfiguration可以加深我们对spring boot的理解。
1、定义Type-safe Configuration Properties
@ConfigurationProperties("author")//1
public class AuthorPropertis {
private static final String NAME = "pyj";
private static final String PWD = "12324";
private String name = NAME;//2
private String pwd = PWD;
private String[] arrayProps;//3
private Properties properties = new Properties();//4
private List<Map<String, Object>> listProp1 = new ArrayList();//5
private List<String> listProp2 = new ArrayList();//6
private Map<String, Object> mapProps = new HashMap();//7
getter and setter...
}
1、@ConfigurationProperties映射application.yml以author为前缀的配置
2、author.name的默认值是pyj
3-7：对于容器对象的属性注入
2、定义一个简单的bean
public class HelloService {
private String msg;
getter and setter...
}
注意：不用纠结HelloService的内容，它就是一个简单的bean。
3、定义AutoConfiguration
@Configuration//1
@ConditionalOnClass(HelloService.class)//2
@EnableConfigurationProperties(AuthorPropertis.class)//3
@ConditionalOnProperty(prefix = "author",value = "enabled",matchIfMissing = true)//4
public class AuthorAutoConfiguration { private final AuthorPropertis authorPropertis; public AuthorAutoConfiguration(AuthorPropertis authorPropertis) {//5
this.authorPropertis = authorPropertis;
} @Bean//6
@ConditionalOnMissingBean(HelloService.class)//7
public HelloService helloService() throws JsonProcessingException {
HelloService helloService = new HelloService();
helloService.setMsg(authorPropertis.getName() +" :" + authorPropertis.getPwd()); ObjectMapper objectMapper = new ObjectMapper();
System.out.println("arrayProps: " + objectMapper.writeValueAsString(authorPropertis.getArrayProps()));
System.out.println("listProp1: " + objectMapper.writeValueAsString(authorPropertis.getListProp1()));
System.out.println("listProp2: " + objectMapper.writeValueAsString(authorPropertis.getListProp2()));
System.out.println("mapProps: " + objectMapper.writeValueAsString(authorPropertis.getMapProps()));
System.out.println("Props: " + objectMapper.writeValueAsString(authorPropertis.getProperties()));
return helloService;
}
}
1、@Configuration声明为一个配置类
2、@ConditionalOnClass表示HelloService在类路径下的时候调用
3、@EnableConfigurationProperties使用AuthorPropertis的配置
4、@ConditionalOnProperty指定的author是否有默认值
5、注入AuthorPropertis
6-7、当不存在HelloService的bean时候，新建一个HelloService的bean
4、在spring.factories注册
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.github.gin.springboot.config.AuthorAutoConfiguration
在resources新建META-INF目录，再新建spring.factories，注册上AuthorAutoConfiguration，让spring boot知道为你自动配置。
如果不明白这个的原理，可以看看@EnableAutoConfiguration通过@Import({EnableAutoConfigurationImportSelector.class})来读取spring.factories
5、配置文件application.yml
debug: true author:
name: pyj
pwd: 1234
properties:
reasonable: 'true'
returnPageInfo: 'true'
listProp1:
- name: abc
value: sgaw
- name: efg
value: sagsag
listProp2:
- config2Value1
- config2Vavlue2
mapProps:
reasonable: true
returnPageInfo: true
arrayProps: 1,2,3,4,5
6、测试
@RestController
public class TestController { @Autowired
HelloService helloService; @RequestMapping("/")
public String index(){
return "hello world!";
} @RequestMapping("/hello")
public String hello(){
return helloService.getMsg();
}
}
运行mvn spring-boot:run，如果看到结果，那么证明是没问题的
上面的AuthorPropertis 、HelloService 、AuthorAutoConfiguration 可以作为一个独立的starter pom为其他项目提供一个通用的服务。虽然spring boot覆盖了大部分的使用场景，但也不是全部都有，但我们也可以利用AutoConfiguration起到同样的效果。
实例代码地址：有爱自取