Servlet利用base64和json向客户端传输图片

更新：这种方法出毛病了！jvm堆溢出了！

原因：byte[] bytes = new byte[fileForInput.available()]这句话在遇到比较大的图片时，开的内存就大，压根就不能这么写！

解决方法一：http://stackoverflow.com/questions/9579874/out-of-memory-when-encoding-file-to-base64

解决方法二：不要传图片了！直接传URL吧！！

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其实跟上一篇blog差不多，客户端还是用HttpURLConnection。

服务器端Servlet在传输图片时，先将图片编码为base64格式（也就是一个字符串），然后放在JSONObject里，顺带着其他数据一起传给客户端。

客户端在收到JSONObject后，将base64格式字符串取出来，再解码写入到一个文件里，得到图片。

OK，下面上代码，服务器端：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
JSONObject json = new JSONObject();
//图片路径
String picPath = getServletContext().getRealPath("")+"/images/XXX.jpg";
String content = ProcessClientData.getPicBASE64(picPath);
json.put("content",content);
json.put("name", "XXX.jpg");
sendJson(json, response);

}
//base64编码函数
public  String getPicBASE64(String picPath) {
String content = "";
try {
FileInputStream fileForInput = new FileInputStream(picPath);
byte[] bytes = new byte[fileForInput.available()];
fileForInput.read(bytes);
content = new sun.misc.BASE64Encoder().encode(bytes);
fileForInput.close();
} catch (Exception e) {
e.printStackTrace();
}
return content;
}
//发送json函数
public void sendJson(JSONObject json,HttpServletResponse response){
try{
response.setCharacterEncoding("UTF-8");
response.setContentType("application/json;charset=UTF-8");
PrintWriter out = response.getWriter();
out.write(json.toString());
out.flush();
out.close();
}catch(Exception e){

}
}

客户端：

JSONObject jsonRec = new JSONObject();
try {
JSONObject  obj = new JSONObject();
//要向服务器发的json
obj.put("xxx", "XXX");
// 创建url资源
URL url = new URL("http://localhost/Test/XXXServlet");
// 建立http连接
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
// 设置允许输出
conn.setDoOutput(true);
conn.setDoInput(true);
// 设置不用缓存
conn.setUseCaches(false);
// 设置传递方式
conn.setRequestMethod("POST");
// 设置维持长连接
conn.setRequestProperty("Connection", "Keep-Alive");
// 设置文件字符集:
conn.setRequestProperty("Charset", "UTF-8");
// 设置文件类型:
conn.setRequestProperty("contentType", "application/json");

// 开始连接请求
conn.connect();
OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
// 写入请求的字符串
writer.write(obj.toString());
writer.flush();
writer.close();

//接收服务器返回的json
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream(),"UTF-8")) ;
String line;
StringBuilder sb = new StringBuilder();
while ((line = br.readLine()) != null) {
sb.append(line);
}
br.close();
conn.disconnect();
jsonRec = JSONObject.fromObject(sb.toString());

} catch (Exception e) {
e.printStackTrace();
}
//处理json
String content = jsonRec.getString("content");
String name = jsonRec.getString("name");

BASE64Decoder decoder = new BASE64Decoder();
try {
// Base64解码
byte[] bytes = decoder.decodeBuffer(content);
for
4000
(int i = 0; i < bytes.length; ++i) {
if (bytes[i] < 0) {// 调整异常数据
bytes[i] += 256;
}
}
// 生成图片
OutputStream outs = new FileOutputStream("C:/users/XXX/Desktop/"+name);
outs.write(bytes);
outs.flush();
outs.close();

} catch (Exception e) {
e.printStackTrace();
}