title: SpringBoot2.動態@Value實現

前面文章有詳細描述過各個不同階段對于bean的擴展接口

所以今天就基于BeanPostProcessor實現Spring中的@Value注解值動態變化

基于上面也可以實現一個配置中心，比如說Apollo

1.通過BeanPostProcessor取得有使用@Value注解的bean,并存儲到map中

2.動態修改map中的bean字段的值

首先寫一個類實現BeanPostProcessor接口，只需要使用其中的一個函數就可以。前后都可以用來實現，并不影響最終的使用，因為咱們只是需要bean的實例。

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;@Configurationpublic 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<Field> fields = findAllField(obj); for (Field field : fields) {Value value = field.getAnnotation(Value.class);if (value != null) { Set<String> 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<Field> findAllField(Class clazz) {final List<Field> res = new LinkedList<>();ReflectionUtils.doWithFields(clazz, new ReflectionUtils.FieldCallback() { @Override public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {res.add(field); }});return res; }}

上面的代碼咱們就已經拿到了SpringValueController這個實例bean并存儲到了map當中，下面看一下測試代碼

/** * cache field,存儲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<String, SpringValue> 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 WeakReference<Object> beanRef; private String beanName; private String key; private String placeholder; private Class<?> targetType; private Type genericType; private boolean isJson; public SpringValue(String key, String placeholder, Object bean, String beanName, Field field, boolean isJson) {this.beanRef = new WeakReference<>(bean);this.beanName = beanName;this.field = field;this.key = key;this.placeholder = placeholder;this.targetType = field.getType();this.isJson = isJson;if (isJson) { this.genericType = field.getGenericType();} } public SpringValue(String key, String placeholder, Object bean, String beanName, Method method, boolean isJson) {this.beanRef = new WeakReference<>(bean);this.beanName = beanName;this.methodParameter = new MethodParameter(method, 0);this.key = key;this.placeholder = placeholder;Class<?>[] paramTps = method.getParameterTypes();this.targetType = paramTps[0];this.isJson = isJson;if (isJson) { this.genericType = method.getGenericParameterTypes()[0];} } public void update(Object newVal) throws IllegalAccessException, InvocationTargetException {if (isField()) { injectField(newVal);} else { injectMethod(newVal);} } private void injectField(Object newVal) throws IllegalAccessException {Object bean = beanRef.get();if (bean == null) { return;}boolean accessible = field.isAccessible();field.setAccessible(true);field.set(bean, newVal);field.setAccessible(accessible); } private void injectMethod(Object newVal) throws InvocationTargetException, IllegalAccessException {Object bean = beanRef.get();if (bean == null) { return;}methodParameter.getMethod().invoke(bean, newVal); } public String getBeanName() {return beanName; } public Class<?> getTargetType() {return targetType; } public String getPlaceholder() {return this.placeholder; } public MethodParameter getMethodParameter() {return methodParameter; } public boolean isField() {return this.field != null; } public Field getField() {return field; } public Type getGenericType() {return genericType; } public boolean isJson() {return isJson; } boolean isTargetBeanValid() {return beanRef.get() != null; } @Override public String toString() {Object bean = beanRef.get();if (bean == null) { return '';}if (isField()) { return String .format('key: %s, beanName: %s, field: %s.%s', key, beanName, bean.getClass().getName(), field.getName());}return String.format('key: %s, beanName: %s, method: %s.%s', key, beanName, bean.getClass().getName(),methodParameter.getMethod().getName()); }}

package 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 = '${'; private static final String PLACEHOLDER_SUFFIX = '}'; private static final String VALUE_SEPARATOR = ':'; private static final String SIMPLE_PLACEHOLDER_PREFIX = '{'; private static final String EXPRESSION_PREFIX = '#{'; private static final String EXPRESSION_SUFFIX = '}'; /** * Resolve placeholder property values, e.g. * <br /> * <br /> * '${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. * <ul> * <li>${some.key} => 'some.key'</li> * <li>${some.key:${some.other.key:100}} => 'some.key', 'some.other.key'</li> * <li>${${some.key}} => 'some.key'</li> * <li>${${some.key:other.key}} => 'some.key'</li> * <li>${${some.key}:${another.key}} => 'some.key', 'another.key'</li> * <li>#{new java.text.SimpleDateFormat(’${some.key}’).parse(’${another.key}’)} => 'some.key', 'another.key'</li> * </ul> */ public Set<String> extractPlaceholderKeys(String propertyString) { Set<String> placeholderKeys = Sets.newHashSet(); if (!isNormalizedPlaceholder(propertyString) && !isExpressionWithPlaceholder(propertyString)) { return placeholderKeys; } Stack<String> stack = new Stack<>(); stack.push(propertyString); while (!stack.isEmpty()) { String strVal = stack.pop(); int startIndex = strVal.indexOf(PLACEHOLDER_PREFIX); if (startIndex == -1) {placeholderKeys.add(strVal);continue; } int endIndex = findPlaceholderEndIndex(strVal, startIndex); if (endIndex == -1) {// invalid placeholder?continue; } String placeholderCandidate = strVal.substring(startIndex + PLACEHOLDER_PREFIX.length(), endIndex); // ${some.key:other.key} if (placeholderCandidate.startsWith(PLACEHOLDER_PREFIX)) {stack.push(placeholderCandidate); } else {// some.key:${some.other.key:100}int separatorIndex = placeholderCandidate.indexOf(VALUE_SEPARATOR);if (separatorIndex == -1) { stack.push(placeholderCandidate);} else { stack.push(placeholderCandidate.substring(0, separatorIndex)); String defaultValuePart = normalizeToPlaceholder(placeholderCandidate.substring(separatorIndex + VALUE_SEPARATOR.length())); if (!Strings.isNullOrEmpty(defaultValuePart)) { stack.push(defaultValuePart); }} } // has remaining part, e.g. ${a}.$ if (endIndex + PLACEHOLDER_SUFFIX.length() < strVal.length() - 1) {String remainingPart = normalizeToPlaceholder(strVal.substring(endIndex + PLACEHOLDER_SUFFIX.length()));if (!Strings.isNullOrEmpty(remainingPart)) { stack.push(remainingPart);} } } return placeholderKeys; } private boolean isNormalizedPlaceholder(String propertyString) { return propertyString.startsWith(PLACEHOLDER_PREFIX) && propertyString.endsWith(PLACEHOLDER_SUFFIX); } private boolean isExpressionWithPlaceholder(String propertyString) { return propertyString.startsWith(EXPRESSION_PREFIX) && propertyString.endsWith(EXPRESSION_SUFFIX)&& propertyString.contains(PLACEHOLDER_PREFIX); } private String normalizeToPlaceholder(String strVal) { int startIndex = strVal.indexOf(PLACEHOLDER_PREFIX); if (startIndex == -1) { return null; } int endIndex = strVal.lastIndexOf(PLACEHOLDER_SUFFIX); if (endIndex == -1) { return null; } return strVal.substring(startIndex, endIndex + PLACEHOLDER_SUFFIX.length()); } private int findPlaceholderEndIndex(CharSequence buf, int startIndex) { int index = startIndex + PLACEHOLDER_PREFIX.length(); int withinNestedPlaceholder = 0; while (index < buf.length()) { if (StringUtils.substringMatch(buf, index, PLACEHOLDER_SUFFIX)) {if (withinNestedPlaceholder > 0) { withinNestedPlaceholder--; index = index + PLACEHOLDER_SUFFIX.length();} else { return index;} } else if (StringUtils.substringMatch(buf, index, SIMPLE_PLACEHOLDER_PREFIX)) {withinNestedPlaceholder++;index = index + SIMPLE_PLACEHOLDER_PREFIX.length(); } else {index++; } } return -1; }}

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@Slf4jpublic 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); }}

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