Java 将图片转成base64，传到前台展示

public String getBase64(SysFile sysFile){
		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();  
	        public String getBase64(SysFile sys