背景
- 学习spring boot的自动配置对于了解整个后端代码运行流程非常重要,只有在了解spring boot是如何配置的情况下,才能在项目的配置中不那么举步维艰.
START
- 假如我们编写了一个用于处理文件信息的工具类,那么我们可以如下操作
工具
- IntelliJ IDEA 2018
步骤
1.创建一个普通的spring boot项目
创建项目
- 注意其中的Group和Artifact,这两项将对应以后使用的依赖参数
<dependency>
<groupId>xyz.crabapple</groupId>
<artifactId>begonia</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
2.项目的目录结构
目录结构
3.现在我们主要代码需要写在begonia目录下
java代码
4.代码解释
BegoniaApplication 为spring boot自己生成的入口类所在的java文件.
Tool 是我的工具类具体实现
public class Tool {
public String prefix;
public Tool(String prefix) {
this.prefix = prefix;
}
/**
* 计算时间戳
* @return 时间戳+五位随机大写字母
*/
public String getStamp() {
String prefix = String.valueOf(new Date().getTime());
prefix=prefix.substring(2,prefix.length());
char[] arr = new char[5];
Random random = new Random();
for (int i = 0; i < 5; i++)
arr[i] = (char) (65 + random.nextInt(26));
String Suffix = String.valueOf(arr);
return prefix + Suffix;
}
- ToolProperties充当配置类和application.properties的桥,即它从application.properties中取具体的配置信息,而真正的配置类需要再到ToolProperties去取.
@ConfigurationProperties(prefix = "Tool")
public class ToolProperties {
private String prefix;
public String getPrefix() {
return prefix;
}
public void setPrefix(String path) {
this.prefix = path;
}
}
- ToolAutoConfiguration是我的具体配置类
@Configuration
@EnableConfigurationProperties(ToolProperties.class)
@ConditionalOnClass(Tool.class)
@ConditionalOnProperty(prefix = "Tool", name="open" ,havingValue="true")
public class ToolAutoConfiguration {
@Autowired
ToolProperties toolProperties;
@Bean
public Tool autoConfiger(){
System.out.println("Tool工具已启动");
System.out.println(toolProperties.getPrefix());
return new Tool(toolProperties.getPrefix());
}
}
- @Configuration 表示这是一个配置类,作用等同于@Component.
以下三个注解都是条件注解,如果有一个不满足条件,自动配置就不会运行. - @EnableConfigurationProperties(ToolProperties.class)
表示配置类的自动配置必须要求ToolProperties.class的存在 - @ConditionalOnClass(Tool.class)
要求功能类存在. - @ConditionalOnProperty(prefix = "Tool", name="open" ,havingValue="true")
查看@ConditionOnProperty
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@Documented
@Conditional(OnPropertyCondition.class)
public @interface ConditionalOnProperty {
/**
* Alias for {@link #name()}.
* @return the names
*/
String[] value() default {};
/**
* A prefix that should be applied to each property. The prefix automatically ends
* with a dot if not specified.
* @return the prefix
*/
String prefix() default "";
/**
* The name of the properties to test. If a prefix has been defined, it is applied to
* compute the full key of each property. For instance if the prefix is
* {@code app.config} and one value is {@code my-value}, the fully key would be
* {@code app.config.my-value}
* <p>
* Use the dashed notation to specify each property, that is all lower case with a "-"
* to separate words (e.g. {@code my-long-property}).
* @return the names
*/
String[] name() default {};
/**
* The string representation of the expected value for the properties. If not
* specified, the property must <strong>not</strong> be equals to {@code false}.
* @return the expected value
*/
String havingValue() default "";
/**
* Specify if the condition should match if the property is not set. Defaults to
* {@code false}.
* @return if should match if the property is missing
*/
boolean matchIfMissing() default false;
/**
* If relaxed names should be checked. Defaults to {@code true}.
* @return if relaxed names are used
*/
boolean relaxedNames() default true;
}
prefix和name拼凑起来表示application.properties的配置信息key,例如我的配置信息为Tool.open=true,那么@ConditionalOnProperty(prefix = "Tool", name="open" ,havingValue="true")就表示配置信息中有这个key就为true,即满足条件,在此条件下若等于注解中havingValue的值,则该注解最终的结果为true.
最后我们需要注册自己的配置类
-
在/src/main目录下创建META-INF目录,并其下创建spring.factories文件,其实spring.factories文件就是一个.properties文件.
- 新建好后,在其中按如下方式书写
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
xyz.crabapple.begonia.ToolAutoConfiguration
- 第一行的org.springframework.boot.autoconfigure.EnableAutoConfiguration就是一个key,第二行的xyz.crabapple.begonia.ToolAutoConfiguration就是我们的自动配置类,即value.配置类还可以按需添加.例如我们找一个依赖看一看
- 找到一个spring boot自带的依赖,可以看到其书写方式,供大家参考.
# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer
