遇到一個需求,圖片須要在瀏覽器離線展現。html
剛開始沒想到什麼辦法,無心中發現kindeditor能夠直接截圖粘貼,沒有上傳就展現出來,查看html元素,發現圖片是已base64展現展示的。java
實現思路:在有網絡的時候,將圖片的base64數據緩存到瀏覽器端的localStorage;無網絡則能夠從localStorage讀取base64數據展現圖片,以base64方式展現圖片以下。spring
一、主要依賴庫數據庫
<dependency> <groupId>commons-codec</groupId> <artifactId>commons-codec</artifactId> <version>1.9</version> </dependency>
二、對圖片的字節碼編碼成base64字符串apache
package com.wss.lsl.demo.base64.service.impl; import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import org.apache.commons.codec.binary.Base64; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.stereotype.Service; import com.wss.lsl.demo.base64.service.ImageService; @Service("imageService") public class ImageServiceImpl implements ImageService { private static final Logger LOG = LoggerFactory.getLogger(ImageServiceImpl.class); @Override public String image2Base64(String imageFile) { LOG.info("圖片轉化爲base64編碼參數:imageFile={}", imageFile); BufferedInputStream bis = null; String result = null; byte[] data = null; try { bis = new BufferedInputStream(new FileInputStream(new File(imageFile))); int count = bis.available(); data = new byte[count]; bis.read(data); result = Base64.encodeBase64String(data); } catch (Exception e) { // ingore } finally { try { bis.close(); } catch (IOException e) { // ingore } } LOG.info("圖片轉化爲base64編碼結果:result={}", result); return result; } }
三、controller獲取base64數據瀏覽器
@Controller @RequestMapping("/base64") public class Base64Controller { private static final Logger LOG = LoggerFactory.getLogger(Base64Controller.class); @Autowired private ImageService imageService; @RequestMapping(value="/show") public String show(Model model, String id){ LOG.info("圖片以base64格式展現"); try { String imageFile = getFilePathFromDb(id); // 從數據庫讀取圖片路徑 String result = imageService.image2Base64(imageFile); model.addAttribute("result", result); } catch (Exception e) { LOG.error("圖片轉化爲base64格式發生異常", e); } return "base64/show"; } }
四、頁面展現圖片緩存
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>以base64格式展現圖片</title> </head> <body> <c:choose> <c:when test="${empty result }"> 圖片編碼失敗 </c:when> <c:otherwise> <img alt="" src="data:image/png;base64,${result }" /> </c:otherwise> </c:choose> </body> </html>