怎么才能將文件流或者圖片轉化為base64，傳到前台展示

圖片轉化為base64，傳到前台展示

public String getBase64(){
        String imgStr = "";
        try {
             
        File file = new File("C:\\EThinkTankFile\\20180402160120431.jpg");
        FileInputStream fis = new FileInputStream(file);
        byte[] buffer = new byte[(int) file.length()]; 
            int offset = 0; 
            int numRead = 0; 
            while (offset < buffer.length && (numRead = fis.read(buffer, offset, buffer.length - offset)) >= 0) {
                offset += numRead;
            } 
             
            if (offset != buffer.length) { 
                throw new IOException("Could not completely read file " 
                        + file.getName()); 
            } 
            fis.close(); 
            BASE64Encoder encoder = new BASE64Encoder();
            imgStr = encoder.encode(buffer);
        } catch (Exception e) {
            e.printStackTrace();
        }
        　　　　　return "data:image/jpeg;base64,"+imgStr;
}前台代碼：<img id="picture" width="690" height="460"  src="">通過ajax 請求將后台返回的字符串 添加到src屬性中去 $("#picture").attr("src","后台返回的base64字符串");

文件流轉化為base64，傳到前台展示

public static String getBase64FromInputStream(InputStream in) {
        // 將圖片文件轉化為字節數組字符串，並對其進行Base64編碼處理
        byte[] data = null;
        // 讀取圖片字節數組
        try {
            ByteArrayOutputStream swapStream = new ByteArrayOutputStream();
            byte[] buff = new byte[100];
            int rc = 0;
            while ((rc = in.read(buff, 0, 100)) > 0) {
                swapStream.write(buff, 0, rc);
            }
            data = swapStream.toByteArray();
        } catch (IOException e) {
            LOGGER.error("InputStream轉換成base64失敗:{}", e);
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    LOGGER.error("InputStream轉換成base64失敗:{}", e);
                }
            }
        }
        //返回的字符串傳到前台，添加到src屬性中去，即可顯示圖片
        return "data:image/jpeg;base64,"+ new String(Base64.encodeBase64(data));
    }