准备工作这里就不说了，包括签约和申请APPID，附上微信开放平台APP开发步骤，不懂的同学可以参考这里：
https://pay./wiki/doc/api/app/app.php?chapter=8_5
上面的步骤很详细，这里主要说下调起支付的注意事项。按照上面文档中说的商户服务器生成支付订单，先调用统一下单API生成预付单，获取到prepay_id后将参数再次签名传输给APP发起支付。
相关代码如下：
/*** 商户服务器生成支付订单，先调用统一下单API(详见第7节)生成预付单，获取到prepay_id后将参数再次签名传输给APP发起支付。*///商品描述String body = "iphone6s";//随机字符串String nonce_str = ResourceUtil.createRandomString(32);//通知地址String notify_url = "http://www./wxpay/pay.php";//商户订单号String out_trade_no = ResourceUtil.generateOutTradeNo(32);//总金额(单位分)int total_fee = 1;String url = "https://api.mch./pay/unifiedorder";String sign = SignUtil.signByMD5("appid=" + Constants.APP_ID + "&body=" + body + "&mch_id=" + Constants.MCH_ID + "&nonce_str=" + nonce_str + "¬ify_url=" + notify_url +"&out_trade_no=" + out_trade_no + "&spbill_create_ip=127.0.0.1" +"&total_fee=" + total_fee + "&trade_type=APP" + "&key=" + Constants.KEY).toUpperCase(Locale.getDefault());//参数以xml格式传递String entity = "<xml><appid>" + Constants.APP_ID + "</appid><mch_id>" + Constants.MCH_ID + "</mch_id><nonce_str>" + nonce_str +"</nonce_str><sign>" + sign + "</sign><body>" + body + "</body><out_trade_no>" + out_trade_no + "</out_trade_no><total_fee>" + total_fee + "</total_fee><spbill_create_ip>127.0.0.1</spbill_create_ip><notify_url>http://www./wxpay/pay.php</notify_url><trade_type>APP</trade_type></xml>"; Log.d("entity", entity);payButton.setEnabled(false);Toast.makeText(PayActivity.this, "获取订单中...", Toast.LENGTH_SHORT).show();byte[] buf = Util.httpPost(url, entity);if (buf != null && buf.length > 0) {String content = new String(buf);Log.d("get server pay params:", content);OrderResult orderResult = ResourceUtil.parseXml(new ByteArrayInputStream(content.getBytes()));if (!TextUtils.equals(orderResult.getReturnCode(), "SUCCESS")) {Toast.makeText(PayActivity.this, orderResult.getReturnMsg(), Toast.LENGTH_SHORT).show();return;} if (!TextUtils.equals(orderResult.getResultCode(), "SUCCESS")) {Toast.makeText(PayActivity.this, orderResult.getErrorDesc(), Toast.LENGTH_SHORT).show();return;}//下单成功，调起支付PayReq request = new PayReq();request.appId = Constants.APP_ID;request.partnerId = Constants.MCH_ID;request.prepayId = orderResult.getPrepayId();request.packageValue = "Sign=WXPay";request.nonceStr = nonce_str;String timeStamp = String.valueOf(System.currentTimeMillis() / 1000);request.timeStamp = timeStamp;request.sign = SignUtil.signByMD5("appid=" + Constants.APP_ID + "&noncestr=" + nonce_str + "&package=Sign=WXPay" +"&partnerid=" + Constants.MCH_ID + "&prepayid=" + orderResult.getPrepayId() + "×tamp=" + timeStamp + "&key=" + Constants.KEY).toUpperCase(Locale.getDefault());api.sendReq(request);payButton.setEnabled(true);}}});
相关参数说明在文档上都注明了，我这里面nonce_str和out_trade_no都是我随机生成的字符创，附上我的工具类，方便大家参考。
ResourceUtil.java
package com.xylpay.sdk.pay.uikit;import java.io.IOException;import java.io.InputStream;import java.util.Random;import org.xmlpull.v1.XmlPullParser;import org.xmlpull.v1.XmlPullParserException;import com.xylpay.sdk.pay.bean.OrderResult;import android.util.Xml;public class ResourceUtil {/*** 随机生成字符串* @param length 字符串的长度* @return 随机字符串*/public static String createRandomString(int length) {String source = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";Random random = new Random();StringBuilder builder = new StringBuilder();for (int i = 0; i < length; i++) {int position = random.nextInt(source.length());builder.append(source.charAt(position));}return builder.toString();}public static String generateOutTradeNo(int n) {StringBuilder builder = new StringBuilder();Random random = new Random();for (int i = 0; i < n; i++) {builder.append(random.nextInt(10));}return builder.toString();}public static OrderResult parseXml(InputStream is) {//PULL解析xml数据XmlPullParser parser = Xml.newPullParser();OrderResult orderResult = null;try {parser.setInput(is, "UTF-8");int type = parser.getEventType();while(type != XmlPullParser.END_DOCUMENT) {switch (type) {case XmlPullParser.START_DOCUMENT:break; case XmlPullParser.START_TAG:if (parser.getName().equals("xml")) {orderResult = new OrderResult();} else if (parser.getName().equals("return_code")) {orderResult.setReturnCode(parser.nextText());} else if (parser.getName().equals("return_msg")) {orderResult.setReturnMsg(parser.nextText());} else if (parser.getName().equals("result_code")) {orderResult.setResultCode(parser.nextText());} else if (parser.getName().equals("err_code_des")) {orderResult.setErrorDesc(parser.nextText());} else if (parser.getName().equals("prepay_id")) {orderResult.setPrepayId(parser.nextText());}break; case XmlPullParser.END_TAG: break; }type = parser.next();}} catch(XmlPullParserException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}return orderResult;}}
其中关于sign的生成，参数的顺序一定要严格按照上面的顺序加上key进行MD5加密，查看签名规范。
关于key的说明，这里的key是需要自己生成然后配置到微信开放平台的，参考商户支付密钥key的生成与设置进行配置，两边需要保持一致。另外，下单时，参数要以xml的格式来传递。
最后附上自己的签名算法：
SignUtil.java
package com.xylpay.sdk.pay.uikit;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;/*** Created by Jackie on /2/15.* * MD5加密*/public class SignUtil {public static String signByMD5(String source) {byte[] bytes = null;try {MessageDigest digest = MessageDigest.getInstance("MD5");digest.update(source.getBytes()); //更新摘要bytes = digest.digest(); //再通过执行诸如填充之类的最终操作完成哈希计算。在调用此方法之后，摘要被重置。} catch (NoSuchAlgorithmException e) {e.printStackTrace();}StringBuilder builder = new StringBuilder(bytes.length * 2);for (byte b : bytes) {/*** 0xFF默认是整形，一个byte跟0xFF相与会先将那个byte转化成整形运算*/if ((b & 0xFF) < 0x10) { //如果为1位 前面补个0builder.append("0");}builder.append(Integer.toHexString(b & 0xFF));}return builder.toString();}}
