常见的问题是检测并显示两个文本的差异（尤其是几百行或几千行）。 使用纯java.lang.String类方法可能是一种解决方案，但是对于此类操作最重要的问题是，“性能”将不能令人满意。 我们需要一种有效的解决方案，其可能具有以下观点：

文字差异工具示例

该问题包含两个部分：

• 检测两个文本的差异：为了检测差异，此解决方案中使用了一种有效的LCS（最长公共子序列）动态算法 。 该解决方案具有O（text1WordCount * text2WordCount）复杂度，并在下面被编码为“ longestCommonSubsequence”方法。
• 可视化差异：为了进行可视化，使用了基于HTML标签的方法，该方法将text2的新单词标记为绿色，将text1的旧单词标记为红色。 此解决方案具有O（changedWordsCount *（text1WordCount + text2WordCount））复杂度，并在下面被编码为“ markTextDifferences”方法。

注意1：为简单起见，“ normalizeText”方法用于删除\ n，\ t和多个空格字符。 注意2：此类创建为Vaadin组件。 但是，“ longestCommonSubsequence”是纯通用的，“ markTextDifferences”方法是基于HTML的可视组件的通用，因此它们也可以用于不同的框架。

import java.util.ArrayList;
import com.vaadin.ui.CustomComponent;
import com.vaadin.ui.Label;
import com.vaadin.ui.Layout;
import com.vaadin.ui.VerticalLayout;/**
* Text comparison component which marks differences of two texts with colors.
* 
* @author cb
*/
public class TextCompareComponent extends CustomComponent {private Layout mainLayout = new VerticalLayout();private ArrayList<String> longestCommonSubsequenceList;private static final String INSERT_COLOR = "#99FFCC";private static final String DELETE_COLOR = "#CB6D6D";public TextCompareComponent(String text1, String text2) {text1 = normalizeText(text1);text2 = normalizeText(text2);this.longestCommonSubsequenceList = longestCommonSubsequence(text1, text2);String result = markTextDifferences(text1, text2, longestCommonSubsequenceList, INSERT_COLOR, DELETE_COLOR);Label label = new Label(result, Label.CONTENT_XHTML);mainLayout.addComponent(label);setCompositionRoot(mainLayout);}/*** Finds a list of longest common subsequences (lcs) of given two texts.* * @param text1* @param text2* @return - longest common subsequence list*/private ArrayList<String> longestCommonSubsequence(String text1,String text2){String[] text1Words = text1.split(" ");String[] text2Words = text2.split(" ");int text1WordCount = text1Words.length;int text2WordCount = text2Words.length;int[][] solutionMatrix = new int[text1WordCount + 1][text2WordCount + 1];for (int i = text1WordCount - 1; i >=0; i--) {for (int j = text2WordCount - 1; j >= 0; j--) {if (text1Words[i].equals(text2Words[j])){solutionMatrix[i][j] = solutionMatrix[i + 1][j + 1] + 1;}else {solutionMatrix[i][j] = Math.max(solutionMatrix[i + 1][j],solutionMatrix[i][j + 1]);}}}int i = 0, j = 0;ArrayList<String> lcsResultList =new ArrayList<String>();while (i < text1WordCount && j < text2WordCount) {if (text1Words[i].equals(text2Words[j])) {lcsResultList.add(text2Words[j]);i++;j++;} else if (solutionMatrix[i + 1][j] >= solutionMatrix[i][j + 1]) {i++;}else {j++;}}return lcsResultList;}/*** Normalizes given string by deleting \n, \t and extra spaces.* * @param text - initial string* @return - normalized string*/private String normalizeText(String text) {text = text.trim();text = text.replace("\n", " ");text = text.replace("\t", " ");while (text.contains("  ")) {text = text.replace("  ", " ");}return text;}/*** Returns colored inserted/deleted text representation of given two texts.* Uses longestCommonSubsequenceList to determine colored sections.** @param text1* @param text2* @param lcsList* @param insertColor* @param deleteColor* @return - colored result text*/private String markTextDifferences(String text1, String text2,ArrayList<String> lcsList, String insertColor, String deleteColor) {StringBuffer stringBuffer = new StringBuffer();if (text1 != null && lcsList != null) {String[] text1Words = text1.split(" ");String[] text2Words = text2.split(" ");int i = 0, j = 0, word1LastIndex = 0, word2LastIndex = 0;for (int k = 0; k < lcsList.size(); k++) {for (i = word1LastIndex, j = word2LastIndex;i < text1Words.length && j < text2Words.length;) {if (text1Words[i].equals(lcsList.get(k)) &&text2Words[j].equals(lcsList.get(k))) {stringBuffer.append("<SPAN>" + lcsList.get(k) + " </SPAN>");word1LastIndex = i + 1;word2LastIndex = j + 1;i = text1Words.length;j = text2Words.length;}else if (!text1Words[i].equals(lcsList.get(k))) {for (; i < text1Words.length &&!text1Words[i].equals(lcsList.get(k)); i++) {stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +deleteColor + "'>" + text1Words[i] + " </SPAN>");}} else if (!text2Words[j].equals(lcsList.get(k))) {for (; j < text2Words.length &&!text2Words[j].equals(lcsList.get(k)), j++) {stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +insertColor + "'>" + text2Words[j] + " </SPAN>");}}}}for (; word1LastIndex < text1Words.length; word1LastIndex++) {stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +deleteColor + "'>" + text1Words[word1LastIndex] + " </SPAN>");}for (; word2LastIndex < text2Words.length; word2LastIndex++) {stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +insertColor + "'>" + text2Words[word2LastIndex] + " </SPAN>");}}return stringBuffer.toString();}
}

参考：我们的JCG合作伙伴 Cagdas Basaraner在CodeBuild博客上使用LCS方法实现了通用文本比较工具 。