SpringBoot2. Implementation of Dynamic @ Value
- 2021-10-24 22:52:57
- OfStack
title: SpringBoot2. Dynamic @ Value implementation
Preface
The extension interface for bean at different stages has been described in detail in the previous article
Therefore, today, based on BeanPostProcessor, the @ Value annotation value in Spring is dynamically changed
Based on the above, one configuration center can also be implemented, such as Apollo
The concrete implementation steps are divided into the following steps
1. Get the bean annotated with @ Value through BeanPostProcessor and store it in map
2. Dynamically modify the value of the bean field in map
Get bean
First, write a class to implement BeanPostProcessor interface, only need to use one of the functions can be. It can be implemented before and after, and does not affect the final use, because we only need an example of bean.
Next, look at the specific implementation code under 1
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<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;
}
}
Above the code we have got SpringValueController this instance bean and stored in map, the following look at the test code 1
/**
* cache field, Storage bean Field
*/
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. ${a}.${b}
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
@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);
}
}