回复图片、音频、视频消息都是需要media_id的，这个是需要将多媒体文件上传到微信服务器才有的。

将多媒体文件上传到微信服务器，以及从微信服务器下载文件，可以参考：http://mp.weixin.qq.com/wiki/index.php?title=上传下载多媒体文件

上传下载多媒体文件的方法还是写到WeixinUtil.java中。

代码如下：

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";
 // 获取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";
 // 创建菜单
 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：获取token的时间,3.过期时间
 public final static Map<String,Object> accessTokenMap = new HashMap<String,Object>();
 /**
 * 发起https请求并获取结果
 * 
 * @param requestUrl 请求地址
 * @param requestMethod 请求方式（GET、POST）
 * @param outputStr 提交的数据
 * @return JSONObject(通过JSONObject.get(key)的方式获取json对象的属性值)
 */
 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错误！");
 } catch (IOException e) {
 e.printStackTrace();
 } catch (NoSuchAlgorithmException e) {
 e.printStackTrace();
 } catch (NoSuchProviderException e) {
 e.printStackTrace();
 } catch (KeyManagementException e) {
 e.printStackTrace();
 }
 return jsonObject;
 }
 
 /**
 * 获取access_token
 *
 * @author qincd
 * @date Nov 6, 2014 9:56:43 AM
 */
 public static AccessToken getAccessToken(String appid,String appSecret) {
 AccessToken at = new AccessToken();
 // 每次获取access_token时，先从accessTokenMap获取，如果过期了就重新从微信获取
 // 没有过期直接返回
 // 从微信获取的token的有效期为2个小时
 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("缓存中发现token未过期，直接从缓存中获取access_token");
 // token未过期，直接从缓存获取返回
 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);
 
 // 每次获取access_token后，存入accessTokenMap
 // 下次获取时，如果没有过期直接从accessTokenMap取。
 accessTokenMap.put("getTokenTime", new Date());
 accessTokenMap.put("token", access_token);
 accessTokenMap.put("expire", expires_in);
 
 return at;
 }
 
 /**
 * 创建菜单
 *
 * @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("菜单创建失败！errorCode:%d,errorMsg:%s",jsonObject.getInt("errcode"),jsonObject.getString("errmsg")));
 return false;
 }
 
 log.info("菜单创建成功！");
 
 return true;
 }
 
 // 上传多媒体文件到微信服务器
 public static final String upload_media_url = "http://file.api.weixin.qq.com/cgi-bin/media/upload?access_token=ACCESS_TOKEN&type=TYPE";
 /**
 * 上传多媒体文件到微信服务器<br>
 * @see http://www.oschina.net/code/snippet_1029535_23824
 * @see http://mp.weixin.qq.com/wiki/index.php?title=上传下载多媒体文件
 *
 * @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");
 
  // 设置边界
  String BOUNDARY = "----------" + System.currentTimeMillis();
  conn.setRequestProperty("Content-Type", "multipart/form-data; boundary="
    + BOUNDARY);
 
  // 请求正文信息
 
  // 第一部分：
  StringBuilder sb = new StringBuilder();
  sb.append("--"); // ////////必须多两道线
  sb.append(BOUNDARY);
  sb.append("rn");
  sb.append("Content-Disposition: form-data;name="file";filename=""
    + file.getName() + ""rn");
  sb.append("Content-Type:application/octet-streamrnrn");
 
  byte[] head = sb.toString().getBytes("utf-8");
 
  // 获得输出流
  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();
 
  // 结尾部分
  byte[] foot = ("rn--" + BOUNDARY + "--rn").getBytes("utf-8");// 定义最后数据分隔线
 
  out.write(foot);
 
  out.flush();
  out.close();
 
  /**
   * 读取服务器响应，必须读取,否则提交不成功
   */
   try {
   // 定义BufferedReader输入流来读取URL的响应
   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("发送POST请求出现异常！" + 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";
 /**
 * 从微信服务器下载多媒体文件
 *
 * @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;
 }
}

测试代码：

public class WeixinUtilTest {

 /**
 *
 * @author qincd
 * @date Nov 6, 2014 9:57:54 AM
 */
 public static void main(String[] args) {
 // 1).获取access_token
 AccessToken accessToken = WeixinUtil.getAccessToken(WeixinUtil.APPID, WeixinUtil.APP_SECRET);
 String filePath = "C:\Users\qince\Pictures\壁纸20141029091612.jpg";
 JSONObject uploadJsonObj = testUploadMedia(filePath,"image",accessToken.getToken());
 if (uploadJsonObj == null) {
 System.out.println("上传图片失败");
 return;
 }
 
 int errcode = 0;
 if (uploadJsonObj.containsKey("errcode")) {
 errcode = uploadJsonObj.getInt("errcode");
 }
 if (errcode == 0) {
 System.out.println("图片上传成功");
 
 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("图片上传失败！");
 
 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);
 }


 /**
 * 上传多媒体文件到微信
 *
 * @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;
 }
 
 /**
 * 从微信下载多媒体文件
 *
 * @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;
 }
}

更多精彩内容请点击《Android微信开发教程汇总》，《java微信开发教程汇总》欢迎大家学习阅读。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持绿夏网。