用Java搭建微信公众号（二）生成access_token

当自己的程序需要访问微信的HTTP接口时，需要传递access_token作为校验的参数。access_token需要通过APPID和APPSecret秘钥来生成，有效期是7200秒，2小时。access_token最好是做成全局变量共享，然后由一个线程定时去刷新，这样可以减少access_token生成的次数，微信服务器对access_token的生成次数有限制。

代码如下，首先是使用HttpClient来发送GET, POST请求的Util类，支持HTTPS

import java.io.File;import java.io.IOException;import java.io.UnsupportedEncodingException;import java.security.cert.CertificateException;import java.security.cert.X509Certificate;import java.util.List;import javax.net.ssl.SSLContext;import javax.net.ssl.TrustManager;import javax.net.ssl.X509TrustManager;import org.apache.http.HttpEntity;import org.apache.http.ParseException;import org.apache.http.client.ClientProtocolException;import org.apache.http.client.entity.UrlEncodedFormEntity;import org.apache.http.client.methods.CloseableHttpResponse;import org.apache.http.client.methods.HttpGet;import org.apache.http.client.methods.HttpPost;import org.apache.http.conn.ssl.SSLConnectionSocketFactory;import org.apache.http.entity.ContentType;import org.apache.http.entity.StringEntity;import org.apache.http.entity.mime.MultipartEntityBuilder;import org.apache.http.entity.mime.content.FileBody;import org.apache.http.entity.mime.content.StringBody;import org.apache.http.impl.client.CloseableHttpClient;import org.apache.http.impl.client.HttpClients;import org.apache.http.message.BasicNameValuePair;import org.apache.http.util.EntityUtils;public class WeixinHttpUtil {/** * HttpClient连接SSL */public static CloseableHttpClient getHTTPSClient() {CloseableHttpClient httpclient = null;try {TrustManager[] tm = { new MyX509TrustManager() };              SSLContext sslContext;sslContext = SSLContext.getInstance("SSL", "SunJSSE");            sslContext.init(null, tm, new java.security.SecureRandom());  SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslContext);httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();} catch (Exception e) {e.printStackTrace();} return httpclient;}public static String postNameValuePair(CloseableHttpClient httpClient, String url, List<BasicNameValuePair> formparams) {String responseBody = "";// 创建httppostHttpPost httppost = new HttpPost(url);UrlEncodedFormEntity uefEntity;try {uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");httppost.setEntity(uefEntity);CloseableHttpResponse response = httpClient.execute(httppost);try {HttpEntity entity = response.getEntity();if (entity != null) {responseBody = EntityUtils.toString(entity, "UTF-8");}} finally {response.close();}} catch (ClientProtocolException e) {e.printStackTrace();} catch (UnsupportedEncodingException e1) {e1.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {// 关闭连接,释放资源try {httpClient.close();} catch (IOException e) {e.printStackTrace();}}return responseBody;}public static String postXml(CloseableHttpClient httpClient, String url, String xml) {String responseBody = "";// 创建httppostHttpPost httppost = new HttpPost(url);try {StringEntity paramEntity = new StringEntity(xml);httppost.setEntity(paramEntity);httppost.setHeader("Content-Type", "text/xml;charset=UTF-8");CloseableHttpResponse response = httpClient.execute(httppost);try {HttpEntity entity = response.getEntity();if (entity != null) {responseBody = EntityUtils.toString(entity, "UTF-8");}} finally {response.close();}} catch (ClientProtocolException e) {e.printStackTrace();} catch (UnsupportedEncodingException e1) {e1.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {// 关闭连接,释放资源try {httpClient.close();} catch (IOException e) {e.printStackTrace();}}return responseBody;}/** * 发送 get请求 */public static String get(CloseableHttpClient httpClient, String url) {String responseBody = "";try {// 创建httpget.HttpGet httpget = new HttpGet(url);// 执行get请求.CloseableHttpResponse response = httpClient.execute(httpget);try {// 获取响应实体HttpEntity entity = response.getEntity();if (entity != null) {responseBody = EntityUtils.toString(entity, "UTF-8");}} finally {response.close();}} catch (ClientProtocolException e) {e.printStackTrace();} catch (ParseException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {// 关闭连接,释放资源try {httpClient.close();} catch (IOException e) {e.printStackTrace();}}return responseBody;}private static class MyX509TrustManager implements X509TrustManager {public void checkClientTrusted(X509Certificate[] chain, String authType)throws CertificateException {}public void checkServerTrusted(X509Certificate[] chain, String authType)throws CertificateException {}public X509Certificate[] getAcceptedIssuers() {return null;}}}

然后是一个单实例的类来提供acces_token的共享，并创建了一个单线程的定时任务来访问微信服务器获取最新的access_token

import java.util.concurrent.Executors;import java.util.concurrent.ScheduledExecutorService;import java.util.concurrent.TimeUnit;import org.apache.http.impl.client.CloseableHttpClient;import com.alibaba.fastjson.JSON;public class AccessTokenUtil {private static AccessTokenUtil instance = new AccessTokenUtil();protected final ScheduledExecutorService executorService;private final static String APP_ID = "";private final static String APP_SECRET = "";private final static String ACCESS_TOKEN_URL = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" + APP_ID + "&secret=" + APP_SECRET;private AccessTokenGetter accessTokenGetter = new AccessTokenGetter();public void start(){//启动定时执行线程池,7000秒刷新一次, Weixin access_token 默认有效期是否7200sexecutorService.scheduleWithFixedDelay(accessTokenGetter, 0, 7000, TimeUnit.SECONDS);} private AccessTokenUtil(){executorService = Executors.newScheduledThreadPool(1);this.start();}public static AccessTokenUtil getInstance(){return instance;}public String getAccessToken(){return accessTokenGetter.getAccessToken();}private static class AccessTokenGetter implements Runnable{private volatile String accessToken = "";public void run() {try {CloseableHttpClient httpClient = WeixinHttpUtil.getHTTPSClient();String accessTokenJSONStr = WeixinHttpUtil.get(httpClient, ACCESS_TOKEN_URL);AccessTokenJSON obj = JSON.parseObject(accessTokenJSONStr, AccessTokenJSON.class);accessToken = obj.getAccess_token();} catch (Exception e) {}}public String getAccessToken(){return accessToken;}}public static void main(String[] args){AccessTokenUtil.getInstance();try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("Token: "  + AccessTokenUtil.getInstance().getAccessToken());}}