Spring4如何自定义@Value功能详解

import org.springframework.stereotype.Service; 
 
/** 
 * 测试Bean 
 */ 
@Service("userService") 
public class UserService { 
 
 public int count() { 
  return 10; 
 } 
  
 public int max(int size) { 
  int count = count(); 
  return count > size ? count : size; 
 } 
} 

import org.springframework.beans.factory.InitializingBean; 
import org.springframework.beans.factory.annotation.Value; 
import org.springframework.stereotype.Component; 
 
@Component 
public class AppRunner implements InitializingBean { 
  
 /** 
  * 引用一个配置项 
  */ 
 @Value("${app.port}") 
 private int port; 
  
 /** 
  * 调用容器的一个bean的方法获取值 
  */ 
 @Value("#{userService.count()}") 
 private int userCount; 
  
 /** 
  * 调用容器的一个bean的方法，且传入一个配置项的值作为参数 
  */ 
 @Value("#{userService.max(${app.size})}") 
 private int max; 
  
 /** 
  * 简单的运算 
  */ 
 @Value("#{${app.size} <= '12345'.length() ? ${app.size} : '12345'.length()}") 
 private int min; 
  
 //测试 
 public void afterPropertiesSet() throws Exception { 
  System.out.println("port : " + port); 
  System.out.println("userCount : " + userCount); 
  System.out.println("max : " + max); 
  System.out.println("min : " + min); 
 } 
} 

app.port=9090 
 
app.size=3 

import org.springframework.context.annotation.AnnotationConfigApplicationContext; 
import org.springframework.context.annotation.ComponentScan; 
import org.springframework.context.annotation.PropertySource; 
 
@ComponentScan 
@PropertySource("classpath:app.properties") 
public class App { 
  
 public static void main( String[] args) { 
  AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(App.class); 
  context.close(); 
 } 
} 

import org.springframework.beans.factory.config.BeanExpressionContext; 
import org.springframework.beans.factory.config.BeanExpressionResolver; 
import org.springframework.beans.factory.config.ConfigurableBeanFactory; 
import org.springframework.context.expression.StandardBeanExpressionResolver; 
 
public class ValueUtil { 
 
 private static final BeanExpressionResolver resolver = new StandardBeanExpressionResolver(); 
  
 /** 
  * 解析一个表达式，获取一个值 
  * @param beanFactory 
  * @param value 一个固定值或一个表达式。如果是一个固定值，则直接返回固定值，否则解析一个表达式，返回解析后的值 
  * @return 
  */ 
 public static Object resolveExpression(ConfigurableBeanFactory beanFactory, String value) { 
  String resolvedValue = beanFactory.resolveEmbeddedValue(value); 
   
  if (!(resolvedValue.startsWith("#{") && value.endsWith("}"))) { 
   return resolvedValue; 
  } 
   
  return resolver.evaluate(resolvedValue, new BeanExpressionContext(beanFactory, null)); 
 } 
} 

import org.springframework.context.annotation.AnnotationConfigApplicationContext; 
import org.springframework.context.annotation.ComponentScan; 
import org.springframework.context.annotation.PropertySource; 
 
@ComponentScan 
@PropertySource("classpath:app.properties") 
public class App { 
  
 public static void main( String[] args) { 
  AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(App.class); 
  //计算一个具体的值（非表达式） 
  System.out.println(ValueUtil.resolveExpression(context.getBeanFactory(), "1121")); 
  //实现@Value的功能 
  System.out.println(ValueUtil.resolveExpression(context.getBeanFactory(), "${app.port}")); 
  System.out.println(ValueUtil.resolveExpression(context.getBeanFactory(), "#{userService.count()}")); 
  System.out.println(ValueUtil.resolveExpression(context.getBeanFactory(), "#{userService.max(${app.size})}")); 
  System.out.println(ValueUtil.resolveExpression(context.getBeanFactory(), "#{${app.size} <= '12345'.length() ? ${app.size} : '12345'.length()}")); 
  context.close(); 
 } 
} 

@Retention(RUNTIME) 
@Target(TYPE) 
public @interface Job { 
 String cron(); 
} 

@Job(cron = "0 0 12 * * ?")
@Job(cron = "${app.job.cron}")