java将图片转为base64返回给前端

@RequestMapping(value = "/captcha")
 public void imagecode(HttpServletRequest request, HttpServletResponse response) throws Exception {
 JSONObject object = new JSONObject();
 CaptchaGenerator vcg = new CaptchaGenerator();
 String vcode = vcg.generatorVCode();
 BufferedImage vcodeImage = vcg.generatorVCodeImage(vcode, true);
 response.setDateHeader("Expires", 0);
 response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");
 response.addHeader("Cache-Control", "post-check=0, pre-check=0");
 response.setHeader("Pragma", "no-cache");
 ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
 response.addHeader("code", vcode.toLowerCase());
 try {
 ImageIO.write(vcodeImage, "png", outputStream);
 BASE64Encoder encoder = new BASE64Encoder();
 String base64 = encoder.encodeBuffer(outputStream.toByteArray()).trim();
 base64 = base64.replaceAll("\n", "").replaceAll("\r", "");
 object.put("code", "data:image/jpg;base64," + base64);
 response.getWriter().write(object.toString());
 } catch (IOException e) {
 response.getWriter().write("");
 } finally {
 if (outputStream != null) {
 outputStream.flush();
 outputStream.close();
 response.getWriter().close();
 }
 }

 }

package com.kinth.security.web.util;


import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.util.Random;

/**
 * 验证码生成器
 * 
 * 
 */
public class CaptchaGenerator {
 
 /**
  * 验证码来源
  */
 final private char[] code = {
  '2', '3', '4', '5', '6', '7', '8', '9',
  'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
  'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 
  'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F',
  'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R',
  'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'
 };
 /**
  * 字体
  */
 final private String[] fontNames = new String[]{
   "黑体", "宋体", "Courier", "Arial", 
   "Verdana", "Times", "Tahoma", "Georgia"};
 /**
  * 字体样式
  */
 final private int[] fontStyles = new int[]{
   Font.BOLD, Font.ITALIC|Font.BOLD
 };
 
 /**
  * 验证码长度
  * 默认4个字符
  */
 private int vcodeLen = 4;
 /**
  * 验证码图片字体大小
  * 默认17
  */
 private int fontsize = 21;
 /**
  * 验证码图片宽度
  */
 private int width = (fontsize+1)*vcodeLen+10;
 /**
  * 验证码图片高度
  */
 private int height = fontsize+12;
 /**
  * 干扰线条数
  * 默认3条
  */
 private int disturbline = 3;
 
 
 public CaptchaGenerator(){}
 
 /**
  * 指定验证码长度
  * @param vcodeLen 验证码长度
  */
 public CaptchaGenerator(int vcodeLen) {
  this.vcodeLen = vcodeLen;
  this.width = (fontsize+1)*vcodeLen+10;
 }
 
 /**
  * 生成验证码图片
  * @param vcode 要画的验证码
  * @param drawline 是否画干扰线
  * @return
  */
 public BufferedImage generatorVCodeImage(String vcode, boolean drawline){
  //创建验证码图片
  BufferedImage vcodeImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
  Graphics g = vcodeImage.getGraphics();
  //填充背景色
  g.setColor(new Color(246, 240, 250));
  g.fillRect(0, 0, width, height);
  if(drawline){
   drawDisturbLine(g);
  }
  //用于生成伪随机数
  Random ran = new Random();
  //在图片上画验证码
  for(int i = 0;i < vcode.length();i++){
   //设置字体
   g.setFont(new Font(fontNames[ran.nextInt(fontNames.length)], fontStyles[ran.nextInt(fontStyles.length)], fontsize));
   //随机生成颜色
   g.setColor(getRandomColor());
   //画验证码
   g.drawString(vcode.charAt(i)+"", i*fontsize+10, fontsize+5);
  }
  //释放此图形的上下文以及它使用的所有系统资源
  g.dispose();
  
  return vcodeImage;
 }
 /**
  * 获得旋转字体的验证码图片
  * @param vcode
  * @param drawline 是否画干扰线
  * @return
  */
 public BufferedImage generatorRotateVCodeImage(String vcode, boolean drawline){
  //创建验证码图片
  BufferedImage rotateVcodeImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
  Graphics2D g2d = rotateVcodeImage.createGraphics();
  //填充背景色
  g2d.setColor(new Color(246, 240, 250));
  g2d.fillRect(0, 0, width, height);
  if(drawline){
   drawDisturbLine(g2d);
  }
  //在图片上画验证码
  for(int i = 0;i < vcode.length();i++){
   BufferedImage rotateImage = getRotateImage(vcode.charAt(i));
   g2d.drawImage(rotateImage, null, (int) (this.height * 0.7) * i, 0);
  }
  g2d.dispose();
  return rotateVcodeImage;
 }
 /**
  * 生成验证码
  * @return 验证码
  */
 public String generatorVCode(){
  int len = code.length;
  Random ran = new Random();
  StringBuffer sb = new StringBuffer();
  for(int i = 0;i < vcodeLen;i++){
   int index = ran.nextInt(len);
   sb.append(code[index]);
  }
  return sb.toString();
 }
 /**
  * 为验证码图片画一些干扰线
  * @param g 
  */
 private void drawDisturbLine(Graphics g){
  Random ran = new Random();
  for(int i = 0;i < disturbline;i++){
   int x1 = ran.nextInt(width);
   int y1 = ran.nextInt(height);
   int x2 = ran.nextInt(width);
   int y2 = ran.nextInt(height);
   g.setColor(getRandomColor());
   //画干扰线
   g.drawLine(x1, y1, x2, y2);
  }
 }
 /**
  * 获取一张旋转的图片
  * @param c 要画的字符
  * @return
  */
 private BufferedImage getRotateImage(char c){
  BufferedImage rotateImage = new BufferedImage(height, height, BufferedImage.TYPE_INT_ARGB);
  Graphics2D g2d = rotateImage.createGraphics();
  //设置透明度为0
  g2d.setColor(new Color(255, 255, 255, 0));
  g2d.fillRect(0, 0, height, height);
  Random ran = new Random();
  g2d.setFont(new Font(fontNames[ran.nextInt(fontNames.length)], fontStyles[ran.nextInt(fontStyles.length)], fontsize));
  g2d.setColor(getRandomColor());
  double theta = getTheta();
  //旋转图片
  g2d.rotate(theta, height/2, height/2);
  g2d.drawString(Character.toString(c), (height-fontsize)/2, fontsize+5);
  g2d.dispose();
  
  return rotateImage;
 }
 /**
  * @return 返回一个随机颜色
  */
 private Color getRandomColor(){
  Random ran = new Random();
  return new Color(ran.nextInt(220), ran.nextInt(220), ran.nextInt(220)); 
 }
 /**
  * @return 角度
  */
 private double getTheta(){
  return ((int) (Math.random()*1000) % 2 == 0 ? -1 : 1)*Math.random();
 }

 /**
  * @return 验证码字符个数
  */
 public int getVcodeLen() {
  return vcodeLen;
 }
 /**
  * 设置验证码字符个数
  * @param vcodeLen
  */
 public void setVcodeLen(int vcodeLen) {
  this.width = (fontsize+3)*vcodeLen+10;
  this.vcodeLen = vcodeLen;
 }
 /**
  * @return 字体大小
  */
 public int getFontsize() {
  return fontsize;
 }
 /**
  * 设置字体大小
  * @param fontsize
  */
 public void setFontsize(int fontsize) {
  this.width = (fontsize+3)*vcodeLen+10;
  this.height = fontsize+15;
  this.fontsize = fontsize;
 }
 /**
  * @return 图片宽度
  */
 public int getWidth() {
  return width;
 }
 /**
  * 设置图片宽度
  * @param width
  */
 public void setWidth(int width) {
  this.width = width;
 }
 /**
  * @return 图片高度
  */
 public int getHeight() {
  return height;
 }
 /**
  * 设置图片高度
  * @param height 
  */
 public void setHeight(int height) {
  this.height = height;
 }
 /**
  * @return 干扰线条数
  */
 public int getDisturbline() {
  return disturbline;
 }
 /**
  * 设置干扰线条数
  * @param disturbline
  */
 public void setDisturbline(int disturbline) {
  this.disturbline = disturbline;
 }
 
}

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
 pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
<script src="../static/model/js/jquery-1.11.2.min.js"></script>
</head>
<body>

 <img id="randomImage" src="" />
 <script type="text/javascript">
 $(function() {
 refreshimg();
 })
 function refreshimg() {
 $.ajax({
 type : "POST",
 dataType : "json",
 url : "../article/captcha",
 success : function(data) {
  console.log('base64=' + data.codePic);
  $('#randomImage').attr('src', data.code);
 },
 error : function() {
 }
 });
 
 $("#randomImage").click(refreshimg)

 }
 </script>

</body>
</html>