上文中简单介绍了intellij环境下Spring Boot的入门示例,从而见识到了Spring Boot的强大,几乎不用做什么配置,就能运行一个Spring mvc的示例,要知道,Spring之前都是以繁琐的配置而为人诟病,Spring Boot的自动装配,可以根据pom的依赖配置,自动生成相应的bean,并加载到Spring Context中,简化了Spring项目搭建的复杂度,本节主要介绍Spring Boot自动装配的流程,并最终提供了自定义自动装配的示例代码。
一、在这之前,首先要介绍一下Spring4中的条件注解:@Conditional,Spring会根据独立的注解条件来创建类,Spring条件注解示例如下:
1、首先创建ch2_1工程和condmodule模块,项目结构如下所示:
2、创建对应的条件类,其中,MatchCondition表示匹配的条件类,NotMatchCondition表示不匹配的条件类,MatchCondition代码如下:
package com.flagship.condition;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class MatchCondition implements Condition {
@Override
public boolean matches(ConditionContext conditionContext,
AnnotatedTypeMetadata annotatedTypeMetadata) {
return true;
}
}
NotMatchCondition代码如下:
package com.flagship.condition;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
public class NotMatchCondition implements Condition {
@Override
public boolean matches(ConditionContext conditionContext,AnnotatedTypeMetadata annotatedTypeMetadata) {
return false;
}
}
3、创建2个类,MatchBean和NotMatchBean,实现同一接口BeanInterface,后续Java配置类中,会根据不同的注解条件,生成相应的类对象,我们用类中的description()来打印信息,以此识别不同的对象信息,BeanInterface代码如下:
package com.flagship.bean;
public interface BeanInterface {
public void description();
}
MatchBean代码如下:
package com.flagship.bean;
public class MatchBean implements BeanInterface {
@Override
public void description() {
System.out.println("this is MatchBean's method!");
}
}
NotMatchBean代码如下:
package com.flagship.bean;
public class NotMatchBean implements BeanInterface {
@Override
public void description() {
System.out.println("this is NotMatchBean's method!");
}
}
4、Java配置类代码如下,此处采用@Configuration注解声明配置类,类似以前的xml配置文件,@Bean注解声明当前方法的返回值是一个Bean对象:
package com.flagship.config;
import com.flagship.bean.BeanInterface;
import com.flagship.bean.MatchBean;
import com.flagship.bean.NotMatchBean;
import com.flagship.condition.MatchCondition;
import com.flagship.condition.NotMatchCondition;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
@Configuration
public class ConditionalCfg {
@Bean
@Conditional(MatchCondition.class)
public BeanInterface getMatchBeanObject(){
return new MatchBean();
}
@Bean
@Conditional(NotMatchCondition.class)
public BeanInterface getNotMatchBeanObject(){
return new NotMatchBean();
}
}
5、运行类代码如下,根据条件类的matches方法的返回值,最终会调用MatchBean类的description方法:
package com.flagship.condmodule;
import com.flagship.bean.BeanInterface;
import com.flagship.config.ConditionalCfg;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Application {
public static void main(String[] args) {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(ConditionalCfg.class);
BeanInterface bean = ctx.getBean(BeanInterface.class);
bean.description();
}
}
最终控制台打印信息为:this is MatchBean's method!
二、跟踪官网文档说明,Spring Boot条件注解大致分了如下几类如下:
Class conditions:@ConditionalOnClass和@ConditionalOnMissingClass,表示类是否在类路径下的条件注解
Bean conditions:@ConditionalOnBean和@ConditionalOnMissingBean,表示Bean是否被定义的条件注解
Property conditions:@ConditionalOnProperty,使用prefix和name属性用来表示是否有值,默认的话,只要该属性存在值,且不为false,即可匹配
Resource conditions:@ConditionalOnResource表示是否存在指定的resouce的条件注解
Web application conditions:@ConditionalOnWebApplication和@ConditionalOnNotWebApplication,当项目是web项目,或者不是web项目的条件注解
SpEL expression conditions:@ConditionalOnExpression,根据SPEL表达式执行结果作为条件
自动装配代码跟踪:
我们从上一章节的@SpringBootApplication开始,由于@SpringBootApplication是由@EnableAutoConfiguration组成的,我们观察@EnableAutoConfiguration注解的源码如下:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package org.springframework.boot.autoconfigure;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({EnableAutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
Class>[] exclude() default {};
String[] excludeName() default {};
}
EnableAutoConfiguration使用@Import注解将EnableAutoConfigurationImportSelector导入并声明为一个Bean,跟踪EnableAutoConfigurationImportSelector的源码,发现其继承AutoConfigurationImportSelector类,而其中有这么一个方法getCandidateConfigurations
protected List getCandidateConfigurations(AnnotationMetadata metadata,AnnotationAttributes attributes) {
List configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
//...省略其余代码
}
继续跟踪SpringFactoriesLoader.loadFactoryNames方法,其代码如下:
public static List loadFactoryNames(Class> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") :ClassLoader.getSystemResources("META-INF/spring.factories");
ArrayList result = new ArrayList();
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
发现最终读取的就是META-INF/spring.factories文件,点击intellij中【External Libraries】中spring-boot-autoconfigure-1.5.7.RELEASE.jar,打开META-INF/spring.factories文件,查看里面内容
此文件中提供了Spring Boot的默认自动配置,随便点开启动一个配置类:org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,代码如下:
@Configuration
@ConditionalOnWebApplication
@ConditionalOnClass({Servlet.class, DispatcherServlet.class, WebMvcConfigurerAdapter.class})
@ConditionalOnMissingBean({WebMvcConfigurationSupport.class})
@AutoConfigureOrder(-2147483638)
@AutoConfigureAfter({DispatcherServletAutoConfiguration.class,
ValidationAutoConfiguration.class})
public class WebMvcAutoConfiguration {
public static final String DEFAULT_PREFIX = "";
public static final String DEFAULT_SUFFIX = "";
public WebMvcAutoConfiguration() {
}
可以看到,这里使用了上述介绍的条件注解来实现自动装配功能
三、本节我们根据上面介绍的原理,开始自定义实现一个自动装配,实现根据项目properties文件的配置打印当前环境信息日志的功能
1、首先,新建一个maven-archetype-quickstart模版的maven模块,并在src\main目录下建好resources\META-INF\spring.factories文件,架构如下图所示:
2、pom文件中加入autofigure的依赖,代码如下:
ch2_1
com.flagship
0.0.1-SNAPSHOT
4.0.0
autocfg
jar
envLog
http://maven.apache.org
UTF-8
org.springframework.boot
spring-boot-autoconfigure
1.5.7.RELEASE
junit
junit
3.8.1
test
3、新建Java配置类:LogServiceProp,会读取项目配置文件中"env.log"开头的属性值
package com.flagship.autocfg;
import org.springframework.boot.context.properties.ConfigurationProperties;
/**
* Java配置类
*/
@ConfigurationProperties(prefix="env.log")
public class LogServiceProp {
private String runPattern = "run";
public String getRunPattern() {
return runPattern;
}
public void setRunPattern(String runPattern) {
this.runPattern = runPattern;
}
}
4、新建业务实体类,用于打印日志,其中,printEnv方法用来在控制台打印当前的运行模式日志,代码如下:
package com.flagship.autocfg;
public class LogService {
private String runPatternLog;
public String printEnv(){
return "current env is in:" + runPatternLog + " pattern!";
}
public String getRunPatternLog() {
return runPatternLog;
}
public void setRunPatternLog(String runPatternLog) {
this.runPatternLog = runPatternLog;
}
}
5、建立自动配置类:LogConfiguration,其中@Configuration注解标识的类,表明作为一个配置类,类似于之前的xml配置文件,@EnableConfigurationProperties告诉Spring Boot 任何被@ConfigurationProperties注解的beans将自动被属性配置,@ConditionalOnClass用来条件注解,当LogService.class存在类路径的时候起效,@ConditionalOnMissingBean当容器中没有这个Bean对象的时候,自动配置这个Bean对象,代码如下:
package com.flagship.autocfg;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
@EnableConfigurationProperties(LogServiceProp.class)
@ConditionalOnClass(LogService.class)
public class LogConfiguration {
@Autowired
private LogServiceProp logServiceProp;
@Bean
@ConditionalOnMissingBean(LogService.class)
public LogService getLogService(){
LogService service = new LogService();
service.setRunPatternLog(logServiceProp.getRunPattern());
return service;
}
}
6、spring.factories文件中加入自动配置类,代码如下:
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.flagship.autocfg.LogConfiguration
7、回到第一节的condmodule模块,pom加入对envLog模块的依赖,代码如下:
com.flagship
autocfg
0.0.1-SNAPSHOT
8、src\main\resources\application.properties中加入如下配置:
env.log.runPattern=debug
9、新建mvc入口测试类,代码如下:
package com.flagship.condmodule;
import com.flagship.autocfg.LogService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@SpringBootApplication
public class AutoCfgApplication {
@Autowired
LogService service;
@RequestMapping("/")
public String getEnvLog(){
return service.printEnv();
}
public static void main(String[] args) {
SpringApplication.run(AutoCfgApplication.class,args);
}
}
10、运行后结果如下,此时神奇的效果出现了,工程中并没有配置LogService这个对象,但是却可以通过@Autowired注解进行注入,这就是Spring Boot自动配置的威力:
current env is in:debug pattern!