replace各个方法的定义
一、replaceFirst方法
public String replaceFirst(String regex, String replacement) {
return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
}
二、replace方法
public String replace(CharSequence target, CharSequence replacement) {
return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
}
三、replaceAll方法
public String replaceAll(String regex, String replacement) {
return Pattern.compile(regex).matcher(this).replaceAll(replacement);
}
replace各个方法的原理
我们通过以下的例子来分析他们的原理。
@Test
public void stringReplace() {
replaceFirst("year = 1929. month=07, day=29, other=\\d{2}");
}//需要获取资料的朋友请加Q君样：290194256*
public void replaceFirst(String string) {
System.out.println(string.replaceFirst("\\d{2}", "--"));
System.out.println(string.replace("\\d{2}", "--"));
System.out.println(string.replace("29", "--"));
System.out.println(string.replaceAll("\\d{2}", "--"));
}
// year = --29. month=07, day=29, other=\d{
2}
// year = 1929. month=07, day=29, other=--
// year = 19--. month=07, day=--, other=\d{
2}
// year = ----. month=--, day=--, other=\d{
2}
一、首先我们分析一下replaceFirst与replaceAll方法，他们的区别在于Pattern构建之后Matcher调用的方法不同。一个是reaplceFirst、一个是replaceAll方法。这两个方法现在可以分析一下。
1、首先对于Matcher的replceFirst方法：可以看到只调用一下的appendReplacement和appendTail方法。关于appendReplacement方法后面可以贴出源码，实现比较复杂
public String replaceFirst(String replacement) {
if (replacement == null)
throw new NullPointerException("replacement");
reset();
if (!find())
return text.toString();
StringBuffer sb = new StringBuffer();
appendReplacement(sb, replacement);
appendTail(sb);
return sb.toString();
}//需要获取资料的朋友请加Q君样：290194256*
2、对于Matcher的replceAll方法，和上述的replaceFirst方法类似。只不过是多次调用了appendReplacement的替换函数。直到没有匹配为止
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();
}//需要获取资料的朋友请加Q君样：290194256*
return text.toString();
}
二、对于replace方法，和上述的replaceAll方法主要有以下两种区别。
1、在Pattern.compile时，添加了Pattern.LITERAL的flag，表示pattern会把regex当作纯文本来处理了。比如\d{2}不转义成两个0-9的数字，而是当作纯文本\d{2}看待。
2、在调用MatcherMatcher.quoteReplacement(replacement.toString())方法对replacement做了对特殊符号($和)作去除转义的操作。
public static String quoteReplacement(String s) {
if ((s.indexOf('\\') == -1) && (s.indexOf('$') == -1))
return s;
StringBuilder sb = new StringBuilder();
for (int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if (c == '\\' || c == '$') {
sb.append('\\');
}
sb.append(c);
}//需要获取资料的朋友请加Q君样：290194256*
return sb.toString();
但是为何只对\和$做处理呢？
三、以下是我们的重点appendReplacement方法
1 public Matcher appendReplacement(StringBuffer sb, String replacement) {
2
3 // If no match, return error
4 if (first < 0)
5 throw new IllegalStateException("No match available");
6
7 // Process substitution string to replace group references with groups
8 int cursor = 0;
9 StringBuilder result = new StringBuilder();
10
11 while (cursor < replacement.length()) {
12 char nextChar = replacement.charAt(cursor);
13 if (nextChar == '\\') {
14 cursor++;
15 if (cursor == replacement.length())
16 throw new IllegalArgumentException("character to be escaped is missing");
17 nextChar = replacement.charAt(cursor);
18 result.append(nextChar);
19 cursor++;
20 } else if (nextChar == '$') {
21 // Skip past $
22 cursor++;
23 // Throw IAE if this "$" is the last character in replacement
24 if (cursor == replacement.length())
25 throw new IllegalArgumentException("Illegal group reference: group index is missing");
26 nextChar = replacement.charAt(cursor);
27 int refNum = -1;
28 if (nextChar == '{') {
29 cursor++;
30 StringBuilder gsb = new StringBuilder();
31 while (cursor < replacement.length()) {
32 nextChar = replacement.charAt(cursor);
33 if (ASCII.isLower(nextChar) ||
34 ASCII.isUpper(nextChar) ||
35 ASCII.isDigit(nextChar)) {
36 gsb.append(nextChar);
37 cursor++;
38 } else {
39 break;
40 }
41 }
42 if (gsb.length() == 0)
43 throw new IllegalArgumentException("named capturing group has 0 length name");
44 if (nextChar != '}')
45 throw new IllegalArgumentException("named capturing group is missing trailing '}'");
46 String gname = gsb.toString();
47 if (ASCII.isDigit(gname.charAt(0)))
48 throw new IllegalArgumentException("capturing group name {" + gname + "} starts with digit character");
49 if (!parentPattern.namedGroups().containsKey(gname))
50 throw new IllegalArgumentException("No group with name {" + gname + "}");
51 refNum = parentPattern.namedGroups().get(gname);
52 cursor++;
53 } else {
54 // The first number is always a group
55 refNum = (int)nextChar - '0';
56 if ((refNum < 0)||(refNum > 9))
57 throw new IllegalArgumentException("Illegal group reference");
58 cursor++;
59 // Capture the largest legal group string
60 boolean done = false;
61 while (!done) {
62 if (cursor >= replacement.length()) {
63 break;
64 }
65 int nextDigit = replacement.charAt(cursor) - '0';
66 if ((nextDigit < 0)||(nextDigit > 9)) {
// not a number
67 break;
68 }
69 int newRefNum = (refNum * 10) + nextDigit;
70 if (groupCount() < newRefNum) {
71 done = true;
72 } else {
73 refNum = newRefNum;
74 cursor++;
75 }
76 }
77 }
78 // Append group
79 if (start(refNum) != -1 && end(refNum) != -1)
80 result.append(text, start(refNum), end(refNum));
81 } else {
82 result.append(nextChar);
83 cursor++;
84 }
85 }//需要获取资料的朋友请加Q君样：290194256*
86 // Append the intervening text
87 sb.append(text, lastAppendPosition, first);
88 // Append the match substitution
89 sb.append(result);
90
91 lastAppendPosition = last;
92 return this;
93 }
四、以下是appendTail的代码
public StringBuffer appendTail(StringBuffer sb) {
sb.append(text, lastAppendPosition, getTextLength());
return sb;
}
