我需要以最有效的方式替换字符串中的许多不同的子字符串。 除了使用string.replace替换每个字段的蛮力方式之外还有另一种方法吗？
答案 0 :(得分：91)
如果您正在操作的字符串很长，或者您在许多字符串上操作，那么使用java.util.regex.Matcher（这需要预先编译时间，所以它赢了'）是值得的。如果您的输入非常小或搜索模式经常变化，则效率很高。
下面是一个完整的示例，基于从地图中获取的令牌列表。 （使用来自Apache Commons Lang的StringUtils）。
Map<String,String> tokens = new HashMap<String,String>();
tokens.put("cat", "Garfield");
tokens.put("beverage", "coffee");
String template = "%cat% really needs some %beverage%.";
// Create pattern of the format "%(cat|beverage)%"
String patternString = "%(" + StringUtils.join(tokens.keySet(), "|") + ")%";
Pattern pattern = Pattern.compile(patternString);
Matcher matcher = pattern.matcher(template);
StringBuffer sb = new StringBuffer();
while(matcher.find()) {
matcher.appendReplacement(sb, tokens.get(matcher.group(1)));
}
matcher.appendTail(sb);
System.out.println(sb.toString());
编译正则表达式后，扫描输入字符串通常非常快（尽管如果你的正则表达式很复杂或涉及回溯，那么你仍然需要进行基准测试以确认这一点！）
答案 1 :(得分：48)
替换匹配字符串（没有正则表达式）的最有效方法之一是使用Aho-Corasick algorithm和性能Trie（发音为“try”），快速hashing算法，高效collections实施。
一个简单的解决方案利用了Apache的StringUtils.replaceEach，如下所示：
private String testStringUtils(
final String text, final Map<String, String> definitions ) {
final String[] keys = keys( definitions );
final String[] values = values( definitions );
return StringUtils.replaceEach( text, keys, values );
}
这会减慢大文本的速度。
Bor's implementation引入了更多的复杂性，通过使用具有相同方法签名的façade成为实现细节：
private String testBorAhoCorasick(
final String text, final Map<String, String> definitions ) {
// Create a buffer sufficiently large that re-allocations are minimized.
final StringBuilder sb = new StringBuilder( text.length() << 1 );
final TrieBuilder builder = Trie.builder();
builder.onlyWholeWords();
builder.removeOverlaps();
final String[] keys = keys( definitions );
for( final String key : keys ) {
builder.addKeyword( key );
}
final Trie trie = builder.build();
final Collection<Emit> emits = trie.parseText( text );
int prevIndex = 0;
for( final Emit emit : emits ) {
final int matchIndex = emit.getStart();
sb.append( text.substring( prevIndex, matchIndex ) );
sb.append( definitions.get( emit.getKeyword() ) );
prevIndex = emit.getEnd() + 1;
}
// Add the remainder of the string (contains no more matches).
sb.append( text.substring( prevIndex ) );
return sb.toString();
}
对于基准测试，缓冲区是使用randomNumeric创建的，如下所示：
private final static int TEXT_SIZE = 1000;
private final static int MATCHES_DIVISOR = 10;
private final static StringBuilder SOURCE
= new StringBuilder( randomNumeric( TEXT_SIZE ) );
MATCHES_DIVISOR指示要注入的变量数量：
private void injectVariables( final Map<String, String> definitions ) {
for( int i = (SOURCE.length() / MATCHES_DIVISOR) + 1; i > 0; i-- ) {
final int r = current().nextInt( 1, SOURCE.length() );
SOURCE.insert( r, randomKey( definitions ) );
}
}
基准代码本身（JMH似乎有点矫枉过正）：
long duration = System.nanoTime();
final String result = testBorAhoCorasick( text, definitions );
duration = System.nanoTime() - duration;
System.out.println( elapsed( duration ) );
一个简单的微基准测试，包含1,000,000个字符和1,000个随机放置的字符串。
没有比赛。
使用10,000个字符和1,000个匹配的字符串替换：
分歧关闭。
使用1,000个字符和10个匹配的字符串替换：
对于短字符串，设置Aho-Corasick的开销会使StringUtils.replaceEach的蛮力方法黯然失色。
基于文本长度的混合方法是可行的，以充分利用这两种实现方式。
考虑比较长度超过1 MB的文本的其他实现，包括：
与算法有关的论文和信息：
答案 2 :(得分：7)
如果您要多次更改String，那么使用StringBuilder （但衡量您的性能以查找）通常会更有效：
String str = "The rain in Spain falls mainly on the plain";
StringBuilder sb = new StringBuilder(str);
// do your replacing in sb - although you'll find this trickier than simply using String
String newStr = sb.toString();
每次对String执行替换时，都会创建一个新的String对象，因为Strings是不可变的。 StringBuilder是可变的，也就是说，它可以根据需要进行更改。
答案 3 :(得分：4)
StringBuilder将更有效地执行替换，因为它的字符数组缓冲区可以指定为所需的长度。StringBuilder的目的不仅仅是追加！
当然真正的问题是这是否是一个优化太过分了？ JVM非常擅长处理多个对象的创建和随后的垃圾收集，就像所有优化问题一样，我的第一个问题是你是否已经测量了这个并确定它是一个问题。
答案 4 :(得分：4)
这对我有用：
String result = input.replaceAll("string1|string2|string3","replacementString");
示例：
String input = "applemangobananaarefriuits";
String result = input.replaceAll("mango|are|ts","-");
System.out.println(result);
输出： apple-banana-friui-
答案 5 :(得分：2)
如何使用replaceAll()方法？
答案 6 :(得分：2)
Rythm现在发布了一个名为 String interpolation mode 的新功能的java模板引擎，它允许您执行以下操作：
String result = Rythm.render("@name is inviting you", "Diana");
以上情况表明您可以按位置将参数传递给模板。 Rythm还允许您按名称传递参数：
Map<String, Object> args = new HashMap<String, Object>();
args.put("title", "Mr.");
args.put("name", "John");
String result = Rythm.render("Hello @title @name", args);
注意Rythm非常快，比String.format和velocity快2到3倍，因为它将模板编译成java字节代码，运行时性能与StringBuilder的连接非常接近。
链接：
答案 7 :(得分：1)
检查一下：
的String.format（STR，STR []）
...
例如：
String.format（“将你的％s放在你的％s所在的位置”，“钱”，“嘴巴”）;
答案 8 :(得分：1)
以下内容基于Todd Owen's answer。该解决方案存在的问题是，如果替换包含在正则表达式中具有特殊含义的字符，则可能会出现意外结果。我还希望能够选择性地进行不区分大小写的搜索。以下是我提出的建议：
@Test
public void replaceMultipleTest() {
assertNull(ExtStringUtils.replaceMultiple(null, null));
assertNull(ExtStringUtils.replaceMultiple(null, Collections.<String, String>emptyMap()));
assertEquals("", ExtStringUtils.replaceMultiple("", null));
assertEquals("", ExtStringUtils.replaceMultiple("", Collections.<String, String>emptyMap()));
assertEquals("folks, we are not sane anymore. with me, i promise you, we will burn in flames", ExtStringUtils.replaceMultiple("folks, we are not winning anymore. with me, i promise you, we will win big league", makeMap("win big league", "burn in flames", "winning", "sane")));
assertEquals("bcaacbbcaacb", ExtStringUtils.replaceMultiple("abccbaabccba", makeMap("a", "b", "b", "c", "c", "a")));
assertEquals("bcaCBAbcCCBb", ExtStringUtils.replaceMultiple("abcCBAabCCBa", makeMap("a", "b", "b", "c", "c", "a")));
assertEquals("bcaacbbcaacb", ExtStringUtils.replaceMultiple("abcCBAabCCBa", makeMap("a", "b", "b", "c", "c", "a"), false));
assertEquals("c colon backslash temp backslash star dot star ", ExtStringUtils.replaceMultiple("c:\\temp\\*.*", makeMap(".", " dot ", ":", " colon ", "\\", " backslash ", "*", " star "), false));
}
private Map<String, String> makeMap(String ... vals) {
Map<String, String> map = new HashMap<String, String>(vals.length / 2);
for(int i = 1; i < vals.length; i+= 2)
map.put(vals[i-1], vals[i]);
return map;
}
以下是我的单元测试用例：
<%= f.submit "Post", class: "new_post_submit" do %>
<i class="glyphicon glyphicon-pencil"></i>
<% end %>
答案 9 :(得分：0)
public String replace(String input, Map<String, String> pairs) {
// Reverse lexic-order of keys is good enough for most cases,
// as it puts longer words before their prefixes ("tool" before "too").
// However, there are corner cases, which this algorithm doesn't handle
// no matter what order of keys you choose, eg. it fails to match "edit"
// before "bed" in "..bedit.." because "bed" appears first in the input,
// but "edit" may be the desired longer match. Depends which you prefer.
final Map<String, String> sorted =
new TreeMap<String, String>(Collections.reverseOrder());
sorted.putAll(pairs);
final String[] keys = sorted.keySet().toArray(new String[sorted.size()]);
final String[] vals = sorted.values().toArray(new String[sorted.size()]);
final int lo = 0, hi = input.length();
final StringBuilder result = new StringBuilder();
int s = lo;
for (int i = s; i < hi; i++) {
for (int p = 0; p < keys.length; p++) {
if (input.regionMatches(i, keys[p], 0, keys[p].length())) {
/* TODO: check for "edit", if this is "bed" in "..bedit.." case,
* i.e. look ahead for all prioritized/longer keys starting within
* the current match region; iff found, then ignore match ("bed")
* and continue search (find "edit" later), else handle match. */
// if (better-match-overlaps-right-ahead)
// continue;
result.append(input, s, i).append(vals[p]);
i += keys[p].length();
s = i--;
}
}
}
if (s == lo) // no matches? no changes!
return input;
return result.append(input, s, hi).toString();
}
答案 10 :(得分：0)
这是基于上述出色的answer from Dave Jarvis的完整的单类实现。该类会在提供的两种不同算法之间自动进行选择，以实现最高效率。 （此答案适用于只想快速复制和粘贴的人。）
package somepackage
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import org.ahocorasick.trie.Emit;
import org.ahocorasick.trie.Trie;
import org.ahocorasick.trie.Trie.TrieBuilder;
import org.apache.commons.lang3.StringUtils;
/**
* ReplaceStrings, This class is used to replace multiple strings in a section of text, with high
* time efficiency. The chosen algorithms were adapted from: https://stackoverflow.com/a/40836618
*/
public final class ReplaceStrings {
/**
* replace, This replaces multiple strings in a section of text, according to the supplied
* search and replace definitions. For maximum efficiency, this will automatically choose
* between two possible replacement algorithms.
*
* Performance note: If it is known in advance that the source text is long, then this method
* signature has a very small additional performance advantage over the other method signature.
* (Although either method signature will still choose the best algorithm.)
*/
public static String replace(
final String sourceText, final Map<String, String> searchReplaceDefinitions) {
final boolean useLongAlgorithm
= (sourceText.length() > 1000 || searchReplaceDefinitions.size() > 25);
if (useLongAlgorithm) {
// No parameter adaptations are needed for the long algorithm.
return replaceUsing_AhoCorasickAlgorithm(sourceText, searchReplaceDefinitions);
} else {
// Create search and replace arrays, which are needed by the short algorithm.
final ArrayList<String> searchList = new ArrayList<>();
final ArrayList<String> replaceList = new ArrayList<>();
final Set<Map.Entry<String, String>> allEntries = searchReplaceDefinitions.entrySet();
for (Map.Entry<String, String> entry : allEntries) {
searchList.add(entry.getKey());
replaceList.add(entry.getValue());
}
return replaceUsing_StringUtilsAlgorithm(sourceText, searchList, replaceList);
}
}
/**
* replace, This replaces multiple strings in a section of text, according to the supplied
* search strings and replacement strings. For maximum efficiency, this will automatically
* choose between two possible replacement algorithms.
*
* Performance note: If it is known in advance that the source text is short, then this method
* signature has a very small additional performance advantage over the other method signature.
* (Although either method signature will still choose the best algorithm.)
*/
public static String replace(final String sourceText,
final ArrayList<String> searchList, final ArrayList<String> replacementList) {
if (searchList.size() != replacementList.size()) {
throw new RuntimeException("ReplaceStrings.replace(), "
+ "The search list and the replacement list must be the same size.");
}
final boolean useLongAlgorithm = (sourceText.length() > 1000 || searchList.size() > 25);
if (useLongAlgorithm) {
// Create a definitions map, which is needed by the long algorithm.
HashMap<String, String> definitions = new HashMap<>();
final int searchListLength = searchList.size();
for (int index = 0; index < searchListLength; ++index) {
definitions.put(searchList.get(index), replacementList.get(index));
}
return replaceUsing_AhoCorasickAlgorithm(sourceText, definitions);
} else {
// No parameter adaptations are needed for the short algorithm.
return replaceUsing_StringUtilsAlgorithm(sourceText, searchList, replacementList);
}
}
/**
* replaceUsing_StringUtilsAlgorithm, This is a string replacement algorithm that is most
* efficient for sourceText under 1000 characters, and less than 25 search strings.
*/
private static String replaceUsing_StringUtilsAlgorithm(final String sourceText,
final ArrayList<String> searchList, final ArrayList<String> replacementList) {
final String[] searchArray = searchList.toArray(new String[]{});
final String[] replacementArray = replacementList.toArray(new String[]{});
return StringUtils.replaceEach(sourceText, searchArray, replacementArray);
}
/**
* replaceUsing_AhoCorasickAlgorithm, This is a string replacement algorithm that is most
* efficient for sourceText over 1000 characters, or large lists of search strings.
*/
private static String replaceUsing_AhoCorasickAlgorithm(final String sourceText,
final Map<String, String> searchReplaceDefinitions) {
// Create a buffer sufficiently large that re-allocations are minimized.
final StringBuilder sb = new StringBuilder(sourceText.length() << 1);
final TrieBuilder builder = Trie.builder();
builder.onlyWholeWords();
builder.ignoreOverlaps();
for (final String key : searchReplaceDefinitions.keySet()) {
builder.addKeyword(key);
}
final Trie trie = builder.build();
final Collection<Emit> emits = trie.parseText(sourceText);
int prevIndex = 0;
for (final Emit emit : emits) {
final int matchIndex = emit.getStart();
sb.append(sourceText.substring(prevIndex, matchIndex));
sb.append(searchReplaceDefinitions.get(emit.getKeyword()));
prevIndex = emit.getEnd() + 1;
}
// Add the remainder of the string (contains no more matches).
sb.append(sourceText.substring(prevIndex));
return sb.toString();
}
/**
* main, This contains some test and example code.
*/
public static void main(String[] args) {
String shortSource = "The quick brown fox jumped over something. ";
StringBuilder longSourceBuilder = new StringBuilder();
for (int i = 0; i < 50; ++i) {
longSourceBuilder.append(shortSource);
}
String longSource = longSourceBuilder.toString();
HashMap<String, String> searchReplaceMap = new HashMap<>();
ArrayList<String> searchList = new ArrayList<>();
ArrayList<String> replaceList = new ArrayList<>();
searchReplaceMap.put("fox", "grasshopper");
searchReplaceMap.put("something", "the mountain");
searchList.add("fox");
replaceList.add("grasshopper");
searchList.add("something");
replaceList.add("the mountain");
String shortResultUsingArrays = replace(shortSource, searchList, replaceList);
String shortResultUsingMap = replace(shortSource, searchReplaceMap);
String longResultUsingArrays = replace(longSource, searchList, replaceList);
String longResultUsingMap = replace(longSource, searchReplaceMap);
System.out.println(shortResultUsingArrays);
System.out.println("----------------------------------------------");
System.out.println(shortResultUsingMap);
System.out.println("----------------------------------------------");
System.out.println(longResultUsingArrays);
System.out.println("----------------------------------------------");
System.out.println(longResultUsingMap);
System.out.println("----------------------------------------------");
}
}
（如果需要，将它们添加到pom文件中。）
<!-- Apache Commons utilities. Super commonly used utilities.
https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.10</version>
</dependency>
<!-- ahocorasick, An algorithm used for efficient searching and
replacing of multiple strings.
https://mvnrepository.com/artifact/org.ahocorasick/ahocorasick -->
<dependency>
<groupId>org.ahocorasick</groupId>
<artifactId>ahocorasick</artifactId>
<version>0.4.0</version>
</dependency>