java中String.replaceAll方法把换行符(\n)替换为明文显示(\n)或(\\n) |
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最近需要解析一个JSONArray类型的字符串 [{"key":"姓名","value":"XX"},{"key":"资质","value":"从事贵金属投资行业10年 国家期货二级分析师 上金所荣誉长老"},{"key":"其他","value":""}]在key资质对应的value中包含三条分行显示的信息，那么坑就来了，当JSON解析遇到\n（换行）就会抛出异常，那怎么办？ 还好，想到了一个对策，就是使用java原生的String.replaceAll方法先把换行（\n）转换成能明文显示的\n(\\n)。 System.out.println(array.replaceAll("\n","\\n"));结果发现，貌似不对劲，输出结果是这样的？？？？ [{"key":"姓名","value":"XX"},{"key":"资质","value":"从事贵金属投资行业10年n国家期货二级分析师n上金所荣誉长老"},{"key":"其他","value":""}]哇，有毒！怎么只剩下一个n了？？ 为了搞明白什么问题，百度、google？no，我们看源码。 先看一下replaceAll方法的源码 public String replaceAll(String replacement) { reset(); boolean result = find(); if (result) { StringBuffer sb = new StringBuffer(); do { appendReplacement(sb, replacement); result = find(); } while (result); appendTail(sb); return sb.toString(); } return text.toString(); }从该方法中，我们可以看到，该方法中是一直循环直至find()返回false，每一次find匹配到换行（我们调用String.replaceAll时传入的匹配字符串是”\n”）都会执行appendReplacement方法，那么这个家伙到底做了什么呢？ public Matcher appendReplacement(StringBuffer sb, String replacement) { // If no match, return error if (first < 0) throw new IllegalStateException("No match available"); // Process substitution string to replace group references with groups int cursor = 0; StringBuilder result = new StringBuilder(); while (cursor < replacement.length()) { char nextChar = replacement.charAt(cursor); if (nextChar == '\\') { cursor++; nextChar = replacement.charAt(cursor); result.append(nextChar); cursor++; } else if (nextChar == '$') { // Skip past $ cursor++; // A StringIndexOutOfBoundsException is thrown if // this "$" is the last character in replacement // string in current implementation, a IAE might be // more appropriate. nextChar = replacement.charAt(cursor); int refNum = -1; if (nextChar == '{') { cursor++; StringBuilder gsb = new StringBuilder(); while (cursor < replacement.length()) { nextChar = replacement.charAt(cursor); if (ASCII.isLower(nextChar) || ASCII.isUpper(nextChar) || ASCII.isDigit(nextChar)) { gsb.append(nextChar); cursor++; } else { break; } } if (gsb.length() == 0) throw new IllegalArgumentException( "named capturing group has 0 length name"); if (nextChar != '}') throw new IllegalArgumentException( "named capturing group is missing trailing '}'"); String gname = gsb.toString(); if (ASCII.isDigit(gname.charAt(0))) throw new IllegalArgumentException( "capturing group name {" + gname + "} starts with digit character"); if (!parentPattern.namedGroups().containsKey(gname)) throw new IllegalArgumentException( "No group with name {" + gname + "}"); refNum = parentPattern.namedGroups().get(gname); cursor++; } else { // The first number is always a group refNum = (int)nextChar - '0'; if ((refNum < 0)||(refNum > 9)) throw new IllegalArgumentException( "Illegal group reference"); cursor++; // Capture the largest legal group string boolean done = false; while (!done) { if (cursor >= replacement.length()) { break; } int nextDigit = replacement.charAt(cursor) - '0'; if ((nextDigit < 0)||(nextDigit > 9)) { // not a number break; } int newRefNum = (refNum * 10) + nextDigit; if (groupCount() < newRefNum) { done = true; } else { refNum = newRefNum; cursor++; } } } // Append group if (start(refNum) != -1 && end(refNum) != -1) result.append(text, start(refNum), end(refNum)); } else { result.append(nextChar); cursor++; } } // Append the intervening text sb.append(text, lastAppendPosition, first); // Append the match substitution sb.append(result); lastAppendPosition = last; return this; }分析该方法的实现，我们可以发现在while循环的第一行执行了 char nextChar = replacement.charAt(cursor);获取替换目标字符串的第一个字符，我们这里是”\\n”，那么第一个字符就是’\’，然后看第一个if语句 if (nextChar == '\\') { cursor++; nextChar = replacement.charAt(cursor); result.append(nextChar); cursor++; }当该字符为’\’时，cursor会++自增1，然后获取第二个字符’\’，把该字符append到result中，关键之处就在这里了，它把连续的两个反斜杠(‘\\’)变成了一个反斜杠(‘\’)，到这里，问题貌似搞明白了。 那么，我们最终展示\n的写法应该是 System.out.println(array.replaceAll("\n","\\\\n"));展示\\n的写法应该是 System.out.println(array.replaceAll("\n","\\\\\\\\n")); |
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