微信支付v3接口（jsapi，小程序，app）调起支付签名java示例代码

替换参数即可使用

注意：需要按照对应的支付文档填写完整的prepay_id的，例如：

构建签名代码：

package com.wxpay.demo;



import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.Signature;
import java.security.SignatureException;
import java.util.Base64;

public class CreateSign02 {
    String getToken(String appid,String prepay_id) throws IOException, SignatureException, NoSuchAlgorithmException, InvalidKeyException {
        //随机字符串
        String nonceStr = "asdasdffafafgddfvc";//真！随机字符串
        //时间戳
        long timestamp = System.currentTimeMillis() / 1000;
        //从下往上依次生成
        String message = buildMessage(appid, timestamp, nonceStr, prepay_id);
        //签名
        String signature = sign(message.getBytes("utf-8"));
        return  signature ;
    }

    String sign(byte[] message) throws NoSuchAlgorithmException, SignatureException, IOException, InvalidKeyException {
        //签名方式
        Signature sign = Signature.getInstance("SHA256withRSA");
        //私钥，通过MyPrivateKey来获取，这是个静态类可以接调用方法 ，需要的是_key.pem文件的绝对路径配上文件名
        sign.initSign(MyPrivatekey.getPrivateKey("E:\\miyao\\apiclient_key.pem"));
        sign.update(message);

        return Base64.getEncoder().encodeToString(sign.sign());
    }

    /**
     *  按照前端签名文档规范进行排序，\n是换行
     * @param appid
     * @param timestamp
     * @param nonceStr
     * @param prepay_id
     * @return
     */
    String buildMessage(String appid, long timestamp,String nonceStr,String prepay_id) {

        return appid + "\n"
                + timestamp + "\n"
                + nonceStr + "\n"
                + prepay_id + "\n";
    }

}

代码加载商户api证书私钥代码（用于上面的签名生成）：

package com.wxpay.demo;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Base64;
public class MyPrivatekey {
    /**
     * 获取私钥。
     *
     * @param filename 私钥文件路径  (required)
     * @return 私钥对象
     */
    public static PrivateKey getPrivateKey(String filename) throws IOException {

        String content = new String(Files.readAllBytes(Paths.get(filename)), "utf-8");
        try {
            String privateKey = content.replace("-----BEGIN PRIVATE KEY-----", "")
                    .replace("-----END PRIVATE KEY-----", "")
                    .replaceAll("\\s+", "");

            KeyFactory kf = KeyFactory.getInstance("RSA");
            return kf.generatePrivate(
                    new PKCS8EncodedKeySpec(Base64.getMimeDecoder().decode(privateKey)));
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException("当前Java环境不支持RSA", e);
        } catch (InvalidKeySpecException e) {
            throw new RuntimeException("无效的密钥格式");
        }
    }
}