常見的問題是檢測并顯示兩個文本（尤其是幾百行或幾千行）的差異。 使用純java.lang.String類方法可能是一種解決方案，但是對于此類操作最重要的問題是，“性能”將不能令人滿意。 我們需要一種有效的解決方案，其可能具有以下觀點：

文字差異工具示例

該問題包含兩個部分：

• 檢測兩個文本的差異：為了檢測差異，在此解決方案中使用了一種有效的LCS（最長公共子序列）動態算法 。 該解決方案具有O（text1WordCount * text2WordCount）復雜度，并在下面被編碼為“ longestCommonSubsequence”方法。
• 可視化差異：可視化使用基于HTML標記的方法，該方法將text2的新單詞標記為綠色，將text1的舊單詞標記為紅色。 該解決方案具有O（changedWordsCount *（text1WordCount + text2WordCount））復雜度，并在下面被編碼為“ markTextDifferences”方法。

注意1：為簡單起見，“ normalizeText”方法用于刪除\ n，\ t和多個空格字符。 注意2：此類創建為Vaadin組件。 但是，“ longestCommonSubsequence”是純通用的，“ markTextDifferences”方法是基于HTML的可視組件的通用，因此它們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();} }

參考：我們的JCG合作伙伴 Cagdas Basaraner在CodeBuild博客上使用LCS方法實現了通用文本比較工具 。

翻譯自: https://www.javacodegeeks.com/2012/05/generic-text-comparison-tool-with-lcs.html

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