具体的实现步骤分为如下几步
1.通过BeanPostProcessor取得有使用@Value注解的bean,并存储到map中
2.动态修改map中的bean字段的值
获取bean
首先写一个类实现BeanPostProcessor接口，只需要使用其中的一个函数就可以。前后都可以用来实现，并不影响最终的使用，因为咱们只是需要bean的实例。
接下来看一下具体实现代码
package com.allen.apollo;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.annotation.Configuration;
import org.springframework.util.ReflectionUtils;
import java.lang.reflect.Field;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
@Configuration
public class SpringValueProcessor implements BeanPostProcessor {
private final PlaceholderHelper placeholderHelper = new PlaceholderHelper();
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (beanName.equals("springValueController")) {
Class obj = bean.getClass();
List fields = findAllField(obj);
for (Field field : fields) {
Value value = field.getAnnotation(Value.class);
if (value != null) {
Set keys = placeholderHelper.extractPlaceholderKeys(value.value());
for (String key : keys) {
SpringValue springValue = new SpringValue(key, value.value(), bean, beanName, field, false);
SpringValueCacheMap.map.put(key, springValue);
}
}
}
}
return bean;
}
private List findAllField(Class clazz) {
final List res = new LinkedList<>();
ReflectionUtils.doWithFields(clazz, new ReflectionUtils.FieldCallback() {
@Override
public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {
res.add(field);
}
});
return res;
}
} 上面的代码咱们就已经拿到了SpringValueController这个实例bean并存储到了map当中，下面看一下测试代码
/**
* cache field,存储bean 字段
*/
package com.allen.apollo;
import com.google.common.collect.LinkedListMultimap;
import com.google.common.collect.Multimap;
public class SpringValueCacheMap {
public static final Multimap map = LinkedListMultimap.create();
} package com.allen.apollo;
import java.lang.ref.WeakReference;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import org.springframework.core.MethodParameter;
public class SpringValue {
private MethodParameter methodParameter;
private Field field;
private WeakReferencepackage com.allen.apollo;
import com.google.common.base.Strings;
import com.google.common.collect.Sets;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanExpressionContext;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.beans.factory.config.Scope;
import org.springframework.util.StringUtils;
import java.util.Set;
import java.util.Stack;
/**
* Placeholder helper functions.
*/
public class PlaceholderHelper {
private static final String PLACEHOLDER_PREFIX = "${";
private static final String PLACEHOLDER_SUFFIX = "}";
private static final String VALUE_SEPARATOR = ":";
private static final String SIMPLE_PLACEHOLDER_PREFIX = "{";
private static final String EXPRESSION_PREFIX = "#{";
private static final String EXPRESSION_SUFFIX = "}";
/**
* Resolve placeholder property values, e.g.
*
*
* "${somePropertyValue}" -> "the actual property value"
*/
public Object resolvePropertyValue(ConfigurableBeanFactory beanFactory, String beanName, String placeholder) {
// resolve string value
String strVal = beanFactory.resolveEmbeddedValue(placeholder);
BeanDefinition bd = (beanFactory.containsBean(beanName) ? beanFactory
.getMergedBeanDefinition(beanName) : null);
// resolve expressions like "#{systemProperties.myProp}"
return evaluateBeanDefinitionString(beanFactory, strVal, bd);
}
private Object evaluateBeanDefinitionString(ConfigurableBeanFactory beanFactory, String value,
BeanDefinition beanDefinition) {
if (beanFactory.getBeanExpressionResolver() == null) {
return value;
}
Scope scope = (beanDefinition != null ? beanFactory
.getRegisteredScope(beanDefinition.getScope()) : null);
return beanFactory.getBeanExpressionResolver()
.evaluate(value, new BeanExpressionContext(beanFactory, scope));
}
/**
* Extract keys from placeholder, e.g.
* -
*
- ${some.key} => "some.key" *
- ${some.key:${some.other.key:100}} => "some.key", "some.other.key" *
- ${${some.key}} => "some.key" *
- ${${some.key:other.key}} => "some.key" *
- ${${some.key}:${another.key}} => "some.key", "another.key" *
- #{new java.text.SimpleDateFormat("${some.key}").parse("${another.key}")} => "some.key", "another.key" *
package com.allen.apollo;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.lang.reflect.InvocationTargetException;
@RestController
@Slf4j
public class SpringValueController {
@Value("${test:123}")
public String zax;
@Value("${test:123}")
public String test;
@Value(("${zed:zed}"))
public String zed;
@GetMapping("/test")
public String test(String a, String b) {
if (!StringUtils.isEmpty(a)) {
try {
for (SpringValue springValue : SpringValueCacheMap.map.get("test")) {
springValue.update(a);
}
for (SpringValue springValue : SpringValueCacheMap.map.get("zed")) {
springValue.update(b);
}
} catch (IllegalAccessException | InvocationTargetException e) {
e.printStackTrace();
}
}
return String.format("test: %s, zax: %s, zed: %s", test, zax, zed);
}
} 
