PropertyPlaceholderHelper --spring占位符替换工具

占位符替换工具PropertyPlaceholderHelper

作用：

spring自带的占位符替换工具
比如 properties name=zhang  age = 18 zhang18=nice
使用此工具处理 {name}-->zhang  {name}{age}-->zhang18 

使用

直接上一段调用demo，简单明了

源码

这个工具类几乎没有其他依赖 先来看一下两个两个主要方法 1、原始字符串从index位置开始匹配子字符串

    /**
     * 原始字符串从index位置开始匹配子字符串 如果匹配则返回true 否则返回false
     *
     * @param str       原始字符串
     * @param index     开始索引位置
     * @param substring 子字符串
     * @return 是否匹配
     */
    public static boolean substringMatch(CharSequence str, int index, CharSequence substring) {
        for (int j = 0; j < substring.length(); j++) {
            int i = index + j;
            if (i >= str.length() || str.charAt(i) != substring.charAt(j)) {
                return false;
            }
        }
        return true;
    }

2、返回结束占位符的index位置 注意startIndex是开始占位符的位置

  /**
     * 返回结束占位符的index位置
     *
     * @param buf
     * @param startIndex
     * @return
     */
    private int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
        int index = startIndex + this.placeholderPrefix.length();
        //如果在查找结束符的时候发现新的开始占位符+1
        int withinNestedPlaceholder = 0;
        while (index < buf.length()) {
            if (substringMatch(buf, index, this.placeholderSuffix)) {
                //大于0表示找到了其他开始占位符
                if (withinNestedPlaceholder > 0) {
                    withinNestedPlaceholder--;
                    index = index + this.placeholderSuffix.length();
                } else {
                    return index;
                }
            } else if (substringMatch(buf, index, this.simplePrefix)) {
                withinNestedPlaceholder++;
                index = index + this.simplePrefix.length();
            } else {
                index++;
            }
        }
        return -1;
    }

3、主方法 主要原理是递归调用，先替换最内层。注意如果占位符循环的话会抛出异常

    protected String parseStringValue(
            String strVal, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {

        StringBuilder result = new StringBuilder(strVal);

        int startIndex = strVal.indexOf(this.placeholderPrefix);
        while (startIndex != -1) {
            int endIndex = findPlaceholderEndIndex(result, startIndex);
            if (endIndex != -1) {
                String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
                String originalPlaceholder = placeholder;
                if (!visitedPlaceholders.add(originalPlaceholder)) {
                    throw new IllegalArgumentException(
                            "Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
                }
                // Recursive invocation, parsing placeholders contained in the placeholder key.
                placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
                // Now obtain the value for the fully resolved key...
                String propVal = placeholderResolver.resolvePlaceholder(placeholder);
                if (propVal == null && this.valueSeparator != null) {
                    int separatorIndex = placeholder.indexOf(this.valueSeparator);
                    if (separatorIndex != -1) {
                        String actualPlaceholder = placeholder.substring(0, separatorIndex);
                        String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
                        propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
                        if (propVal == null) {
                            propVal = defaultValue;
                        }
                    }
                }
                if (propVal != null) {
                    // Recursive invocation, parsing placeholders contained in the
                    // previously resolved placeholder value.
                    propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
                    result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
                    startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
                } else if (this.ignoreUnresolvablePlaceholders) {
                    // Proceed with unprocessed value.
                    startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
                } else {
                    throw new IllegalArgumentException("Could not resolve placeholder '" +
                            placeholder + "'" + " in string value "" + strVal + """);
                }
                visitedPlaceholders.remove(originalPlaceholder);
            } else {
                startIndex = -1;
            }
        }

        return result.toString();
    }

所有代码都在这里

尝试使用栈来实现占位符替换，可惜尝试几个小时之后失败了

特别注意 发布这个文章到github pages时 这个中的嵌套中括号一直报错，故使用图片替换，希望后能知道引起这个问题的根源

写在最后：