回復圖片、音頻、視頻消息都是需要media_id的，這個是需要將多媒體文件上傳到微信服務器才有的。

將多媒體文件上傳到微信服務器，以及從微信服務器下載文件，可以參考：http://mp.weixin.qq.com/wiki/index.php?title=上傳下載多媒體文件

上傳下載多媒體文件的方法還是寫到WeixinUtil.java中。

代碼如下：

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
 
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
 
import net.sf.json.JSONObject;
 
import org.apache.commons.lang.StringUtils;
import org.apache.log4j.Logger;
 
import com.company.project.model.menu.AccessToken;
import com.company.project.model.menu.Menu;
 
public class WeixinUtil {
 private static Logger log = Logger.getLogger(WeixinUtil.class);
 public final static String APPID = "wxb927d4280e6db674";
 public final static String APP_SECRET = "21441e9f3226eee81e14380a768b6d1e";
 // 獲取access_token的接口地址（GET） 限200（次/天）
 public final static String access_token_url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=APPID&secret=APPSECRET";
 // 創(chuàng)建菜單
 public final static String create_menu_url = "https://api.weixin.qq.com/cgi-bin/menu/create?access_token=ACCESS_TOKEN";
 // 存放：1.token，2：獲取token的時間,3.過期時間
 public final static Map<String,Object> accessTokenMap = new HashMap<String,Object>();
 /**
 * 發(fā)起https請求并獲取結(jié)果
 * 
 * @param requestUrl 請求地址
 * @param requestMethod 請求方式（GET、POST）
 * @param outputStr 提交的數(shù)據(jù)
 * @return JSONObject(通過JSONObject.get(key)的方式獲取json對象的屬性值)
 */
 public static JSONObject handleRequest(String requestUrl,String requestMethod,String outputStr) {
 JSONObject jsonObject = null;
  
 try {
  URL url = new URL(requestUrl);
  HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();
  SSLContext ctx = SSLContext.getInstance("SSL", "SunJSSE");
  TrustManager[] tm = {new MyX509TrustManager()};
  ctx.init(null, tm, new SecureRandom());
  SSLSocketFactory sf = ctx.getSocketFactory();
  conn.setSSLSocketFactory(sf);
  conn.setDoInput(true);
  conn.setDoOutput(true);
  conn.setRequestMethod(requestMethod);
  conn.setUseCaches(false);
   
  if ("GET".equalsIgnoreCase(requestMethod)) {
  conn.connect();
  }
   
  if (StringUtils.isNotEmpty(outputStr)) {
  OutputStream out = conn.getOutputStream();
  out.write(outputStr.getBytes("utf-8"));
  out.close();
  }
   
  InputStream in = conn.getInputStream();
  BufferedReader br = new BufferedReader(new InputStreamReader(in,"utf-8"));
  StringBuffer buffer = new StringBuffer();
  String line = null;
   
  while ((line = br.readLine()) != null) {
  buffer.append(line);
  }
   
  in.close();
  conn.disconnect();
   
  jsonObject = JSONObject.fromObject(buffer.toString());
 } catch (MalformedURLException e) {
  e.printStackTrace();
  log.error("URL錯誤！");
 } catch (IOException e) {
  e.printStackTrace();
 } catch (NoSuchAlgorithmException e) {
  e.printStackTrace();
 } catch (NoSuchProviderException e) {
  e.printStackTrace();
 } catch (KeyManagementException e) {
  e.printStackTrace();
 }
 return jsonObject;
 }
  
 /**
 * 獲取access_token
 *
 * @author qincd
 * @date Nov 6, 2014 9:56:43 AM
 */
 public static AccessToken getAccessToken(String appid,String appSecret) {
 AccessToken at = new AccessToken();
 // 每次獲取access_token時，先從accessTokenMap獲取，如果過期了就重新從微信獲取
 // 沒有過期直接返回
 // 從微信獲取的token的有效期為2個小時
 if (!accessTokenMap.isEmpty()) {
  Date getTokenTime = (Date) accessTokenMap.get("getTokenTime");
  Calendar c = Calendar.getInstance();
  c.setTime(getTokenTime);
  c.add(Calendar.HOUR_OF_DAY, 2);
   
  getTokenTime = c.getTime();
  if (getTokenTime.after(new Date())) {
  log.info("緩存中發(fā)現(xiàn)token未過期，直接從緩存中獲取access_token");
  // token未過期，直接從緩存獲取返回
  String token = (String) accessTokenMap.get("token");
  Integer expire = (Integer) accessTokenMap.get("expire");
  at.setToken(token);
  at.setExpiresIn(expire);
  return at;
  }
 }
 String requestUrl = access_token_url.replace("APPID", appid).replace("APPSECRET", appSecret);
  
 JSONObject object = handleRequest(requestUrl, "GET", null);
 String access_token = object.getString("access_token");
 int expires_in = object.getInt("expires_in");
  
 log.info("\naccess_token:" + access_token);
 log.info("\nexpires_in:" + expires_in);
  
 at.setToken(access_token);
 at.setExpiresIn(expires_in);
  
 // 每次獲取access_token后，存入accessTokenMap
 // 下次獲取時，如果沒有過期直接從accessTokenMap取。
 accessTokenMap.put("getTokenTime", new Date());
 accessTokenMap.put("token", access_token);
 accessTokenMap.put("expire", expires_in);
  
 return at;
 }
  
 /**
 * 創(chuàng)建菜單
 *
 * @author qincd
 * @date Nov 6, 2014 9:56:36 AM
 */
 public static boolean createMenu(Menu menu,String accessToken) {
 String requestUrl = create_menu_url.replace("ACCESS_TOKEN", accessToken);
 String menuJsonString = JSONObject.fromObject(menu).toString();
 JSONObject jsonObject = handleRequest(requestUrl, "POST", menuJsonString);
 String errorCode = jsonObject.getString("errcode");
 if (!"0".equals(errorCode)) {
  log.error(String.format("菜單創(chuàng)建失?。rrorCode:%d,errorMsg:%s",jsonObject.getInt("errcode"),jsonObject.getString("errmsg")));
  return false;
 }
  
 log.info("菜單創(chuàng)建成功！");
  
 return true;
 }
  
 // 上傳多媒體文件到微信服務器
 public static final String upload_media_url = "http://file.api.weixin.qq.com/cgi-bin/media/upload?access_token=ACCESS_TOKEN&type=TYPE";
 /**
 * 上傳多媒體文件到微信服務器<br>
 * @see http://www.oschina.net/code/snippet_1029535_23824
 * @see http://mp.weixin.qq.com/wiki/index.php?title=上傳下載多媒體文件
 *
 * @author qincd
 * @date Nov 6, 2014 4:11:22 PM
 */
 public static JSONObject uploadMediaToWX(String filePath,String type,String accessToken) throws IOException{
 File file = new File(filePath);
 if (!file.exists()) {
  log.error("文件不存在！");
  return null;
 }
  
 String url = upload_media_url.replace("ACCESS_TOKEN", accessToken).replace("TYPE", type);
 URL urlObj = new URL(url);
 HttpURLConnection conn = (HttpURLConnection) urlObj.openConnection();
 conn.setDoInput(true);
 conn.setDoOutput(true);
 conn.setUseCaches(false);
  
 conn.setRequestProperty("Connection", "Keep-Alive");
    conn.setRequestProperty("Charset", "UTF-8");
  
    // 設置邊界
    String BOUNDARY = "----------" + System.currentTimeMillis();
    conn.setRequestProperty("Content-Type", "multipart/form-data; boundary="
        + BOUNDARY);
  
    // 請求正文信息
  
    // 第一部分：
    StringBuilder sb = new StringBuilder();
    sb.append("--"); // ////////必須多兩道線
    sb.append(BOUNDARY);
    sb.append("\r\n");
    sb.append("Content-Disposition: form-data;name=\"file\";filename=\""
        + file.getName() + "\"\r\n");
    sb.append("Content-Type:application/octet-stream\r\n\r\n");
  
    byte[] head = sb.toString().getBytes("utf-8");
  
    // 獲得輸出流
    OutputStream out = new DataOutputStream(conn.getOutputStream());
    out.write(head);
  
    // 文件正文部分
    DataInputStream in = new DataInputStream(new FileInputStream(file));
    int bytes = 0;
    byte[] bufferOut = new byte[1024];
    while ((bytes = in.read(bufferOut)) != -1) {
      out.write(bufferOut, 0, bytes);
    }
    in.close();
  
    // 結(jié)尾部分
    byte[] foot = ("\r\n--" + BOUNDARY + "--\r\n").getBytes("utf-8");// 定義最后數(shù)據(jù)分隔線
  
    out.write(foot);
  
    out.flush();
    out.close();
  
    /**
     * 讀取服務器響應，必須讀取,否則提交不成功
     */
     try {
     // 定義BufferedReader輸入流來讀取URL的響應
     StringBuffer buffer = new StringBuffer();
     BufferedReader reader = new BufferedReader(new InputStreamReader(
     conn.getInputStream()));
     String line = null;
     while ((line = reader.readLine()) != null) {
      buffer.append(line);
     }
      
     reader.close();
     conn.disconnect();
      
     return JSONObject.fromObject(buffer.toString());
     } catch (Exception e) {
     log.error("發(fā)送POST請求出現(xiàn)異常！" + e);
     e.printStackTrace();
     }
 return null;
 }
  
 public static final String download_media_url = "http://file.api.weixin.qq.com/cgi-bin/media/get?access_token=ACCESS_TOKEN&media_id=MEDIA_ID";
 /**
 * 從微信服務器下載多媒體文件
 *
 * @author qincd
 * @date Nov 6, 2014 4:32:12 PM
 */
 public static String downloadMediaFromWx(String accessToken,String mediaId,String fileSavePath) throws IOException {
 if (StringUtils.isEmpty(accessToken) || StringUtils.isEmpty(mediaId)) return null;
  
 String requestUrl = download_media_url.replace("ACCESS_TOKEN", accessToken).replace("MEDIA_ID", mediaId);
 URL url = new URL(requestUrl);
 HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 conn.setRequestMethod("GET");
 conn.setDoInput(true);
 conn.setDoOutput(true);
 InputStream in = conn.getInputStream();
  
 File dir = new File(fileSavePath);
 if (!dir.exists()) {
  dir.mkdirs();
 }
 if (!fileSavePath.endsWith("/")) {
  fileSavePath += "/";
 }
  
 String ContentDisposition = conn.getHeaderField("Content-disposition");
 String weixinServerFileName = ContentDisposition.substring(ContentDisposition.indexOf("filename")+10, ContentDisposition.length() -1);
 fileSavePath += weixinServerFileName; 
 BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(fileSavePath));
 byte[] data = new byte[1024];
 int len = -1;
  
 while ((len = in.read(data)) != -1) {
  bos.write(data,0,len);
 }
  
 bos.close();
 in.close();
 conn.disconnect();
  
 return fileSavePath;
 }
}

測試代碼：

public class WeixinUtilTest {
 
 /**
 *
 * @author qincd
 * @date Nov 6, 2014 9:57:54 AM
 */
 public static void main(String[] args) {
 // 1).獲取access_token
 AccessToken accessToken = WeixinUtil.getAccessToken(WeixinUtil.APPID, WeixinUtil.APP_SECRET);
 String filePath = "C:\\Users\\qince\\Pictures\\壁紙20141029091612.jpg";
 JSONObject uploadJsonObj = testUploadMedia(filePath,"image",accessToken.getToken());
 if (uploadJsonObj == null) {
  System.out.println("上傳圖片失敗");
  return;
 }
  
 int errcode = 0;
 if (uploadJsonObj.containsKey("errcode")) {
  errcode = uploadJsonObj.getInt("errcode");
 }
 if (errcode == 0) {
  System.out.println("圖片上傳成功");
   
  String mediaId = uploadJsonObj.getString("media_id");
  long createAt = uploadJsonObj.getLong("created_at");
  System.out.println("--Details:");
  System.out.println("media_id:" + mediaId);
  System.out.println("created_at:" + createAt);
 }
 else {
  System.out.println("圖片上傳失?。?quot;);
   
  String errmsg = uploadJsonObj.getString("errmsg");
  System.out.println("--Details:");
  System.out.println("errcode:" + errcode);
  System.out.println("errmsg:" + errmsg);
 }
  
 String mediaId = "6W-UvSrQ2hkdSdVQJJXShwtFDPLfbGI1qnbNFy8weZyb9Jac2xxxcAUwt8p4sYPH";
 String filepath = testDownloadMedia(accessToken.getToken(), mediaId, "d:/test");
 System.out.println(filepath);
 }
 
 
 /**
 * 上傳多媒體文件到微信
 *
 * @author qincd
 * @date Nov 6, 2014 4:15:14 PM
 */
 public static JSONObject testUploadMedia(String filePath,String type,String accessToken) {
 try {
  return WeixinUtil.uploadMediaToWX(filePath, type, accessToken);
 } catch (IOException e) {
  e.printStackTrace();
 }
  
 return null;
 }
  
 /**
 * 從微信下載多媒體文件
 *
 * @author qincd
 * @date Nov 6, 2014 4:56:25 PM
 */
 public static String testDownloadMedia(String accessToken,String mediaId,String fileSaveDir) {
 try {
  return WeixinUtil.downloadMediaFromWx(accessToken, mediaId, fileSaveDir);
 } catch (IOException e) {
  e.printStackTrace();
 }
  
 return null;
 }
}

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