Bagaimana untuk melaksanakan SpringBoot2 dinamik @Value

Langkah-langkah pelaksanaan khusus dibahagikan kepada langkah berikut

1 Dapatkan kacang yang diberi penjelasan dengan @Value melalui BeanPostProcessor dan simpannya dalam peta

2 peta Nilai medan

Dapatkan kacang

Mula-mula tulis kelas untuk melaksanakan antara muka BeanPostProcessor, dan hanya perlu menggunakan salah satu fungsinya. Ia boleh dilaksanakan sebelum dan selepas, dan ia tidak menjejaskan penggunaan akhir, kerana kita hanya memerlukan contoh kacang.

Mari kita lihat kod pelaksanaan khusus

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;
    }
}

Dalam kod di atas, kami telah memperoleh kacang contoh SpringValueController dan menyimpannya dalam peta Mari lihat kod ujian

  /**
   * 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<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);
    }
}

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