更新：這種方法出毛病了！jvm堆溢位了！

原因：byte[] bytes = new byte[fileForInput.available()]這句話在遇到比較大的圖片時，開的記憶體就大，壓根就不能這麼寫！

—————————————————————————————

其實跟上一篇blog差不多，客戶端還是用HttpURLConnection。

伺服器端Servlet在傳輸圖片時，先將圖片編碼為base64格式（也就是一個字串），然後放在JSONObject裡，順帶著其他資料一起傳給客戶端。

客戶端在收到JSONObject後，將base64格式字串取出來，再解碼寫入到一個檔案裡，得到圖片。

OK，下面上程式碼，伺服器端：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        JSONObject json = new JSONObject();
        //圖片路徑
        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編碼函式
    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;  
        }  
        //傳送json函式
        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){

            }
        }

客戶端：

        JSONObject jsonRec = new JSONObject();
        try {
            JSONObject  obj = new JSONObject();
            //要向伺服器發的json
            obj.put("xxx", "XXX");
            // 建立url資源
            URL url = new URL("http://localhost/Test/XXXServlet");
            // 建立http連線
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // 設定允許輸出
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 設定不用快取
            conn.setUseCaches(false);
            // 設定傳遞方式
            conn.setRequestMethod("POST");
            // 設定維持長連線
            conn.setRequestProperty("Connection", "Keep-Alive");
            // 設定檔案字符集:
            conn.setRequestProperty("Charset", "UTF-8");
            // 設定檔案型別:
            conn.setRequestProperty("contentType", "application/json");


            // 開始連線請求
            conn.connect();
            OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
            // 寫入請求的字串
            writer.write(obj.toString());
            writer.flush();
            writer.close();


            //接收伺服器返回的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();
        }
        //處理json
        String content = jsonRec.getString("content");
        String name = jsonRec.getString("name");

        BASE64Decoder decoder = new BASE64Decoder();  
        try {  
            // Base64解碼  
            byte[] bytes = decoder.decodeBuffer(content);  
            for (int i = 0; i < bytes.length; ++i) {  
                if (bytes[i] < 0) {// 調整異常資料  
                    bytes[i] += 256;  
                }  
            }  
            // 生成圖片  
            OutputStream outs = new FileOutputStream("C:/users/XXX/Desktop/"+name);  
            outs.write(bytes);  
            outs.flush();  
            outs.close();  

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