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155 lines
4.7 KiB
155 lines
4.7 KiB
# Spring PropertyPlaceholderHelper
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- 类全路径: `org.springframework.util.PropertyPlaceholderHelper`
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## parseStringValue
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- `org.springframework.util.PropertyPlaceholderHelper#parseStringValue` 这个方法是主要方法
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```java
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protected String parseStringValue(
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String value, PlaceholderResolver placeholderResolver, @Nullable Set<String> visitedPlaceholders) {
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// 占位符所在位置
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int startIndex = value.indexOf(this.placeholderPrefix);
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if (startIndex == -1) {
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return value;
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}
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// 返回值
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StringBuilder result = new StringBuilder(value);
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while (startIndex != -1) {
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// 寻找结尾占位符
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int endIndex = findPlaceholderEndIndex(result, startIndex);
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if (endIndex != -1) {
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// 返回值切分留下中间内容
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String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
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String originalPlaceholder = placeholder;
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if (visitedPlaceholders == null) {
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visitedPlaceholders = new HashSet<>(4);
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}
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if (!visitedPlaceholders.add(originalPlaceholder)) {
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throw new IllegalArgumentException(
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"Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
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}
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// Recursive invocation, parsing placeholders contained in the placeholder key.
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// 递归获取占位符内容
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placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
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// Now obtain the value for the fully resolved key...
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// 解析占位符内容获得真正的属性值
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String propVal = placeholderResolver.resolvePlaceholder(placeholder);
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if (propVal == null && this.valueSeparator != null) {
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int separatorIndex = placeholder.indexOf(this.valueSeparator);
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if (separatorIndex != -1) {
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String actualPlaceholder = placeholder.substring(0, separatorIndex);
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String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
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propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
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if (propVal == null) {
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propVal = defaultValue;
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}
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}
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}
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if (propVal != null) {
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// Recursive invocation, parsing placeholders contained in the
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// previously resolved placeholder value.
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propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
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result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
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if (logger.isTraceEnabled()) {
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logger.trace("Resolved placeholder '" + placeholder + "'");
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}
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startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
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}
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else if (this.ignoreUnresolvablePlaceholders) {
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// Proceed with unprocessed value.
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startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
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}
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else {
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throw new IllegalArgumentException("Could not resolve placeholder '" +
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placeholder + "'" + " in value \"" + value + "\"");
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}
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visitedPlaceholders.remove(originalPlaceholder);
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}
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else {
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startIndex = -1;
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}
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}
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return result.toString();
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}
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```
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在这里还需要关注一个接口
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- 占位符解析.
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```java
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@FunctionalInterface
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public interface PlaceholderResolver {
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/**
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* Resolve the supplied placeholder name to the replacement value.
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* @param placeholderName the name of the placeholder to resolve
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* @return the replacement value, or {@code null} if no replacement is to be made
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*/
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@Nullable
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String resolvePlaceholder(String placeholderName);
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}
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```
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占位符解析请查看: [PlaceholderResolver](PlaceholderResolver)
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## findPlaceholderEndIndex
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- 寻找结尾占位符索引
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```java
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/**
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* 寻找结尾占位符索引
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*/
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private int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
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int index = startIndex + this.placeholderPrefix.length();
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int withinNestedPlaceholder = 0;
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while (index < buf.length()) {
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if (StringUtils.substringMatch(buf, index, this.placeholderSuffix)) {
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if (withinNestedPlaceholder > 0) {
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withinNestedPlaceholder--;
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index = index + this.placeholderSuffix.length();
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}
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else {
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return index;
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}
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}
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else if (StringUtils.substringMatch(buf, index, this.simplePrefix)) {
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withinNestedPlaceholder++;
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index = index + this.simplePrefix.length();
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}
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else {
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index++;
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}
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}
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return -1;
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}
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```
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