微信公众号指定用户推送消息以及微信小程序加密数据解密算法

首先需要创建一个maven工程

1.在自己的pom中加入如下代码：

<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcprov-jdk16</artifactId>
    <version>1.46</version>
</dependency>
 
 <dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
    <version>1.4</version>
</dependency>
 
<dependency> 
    <groupId>net.sf.json-lib</groupId> 
    <artifactId>json-lib</artifactId> 
    <version>2.2.3</version> 
    <classifier>jdk15</classifier> 
</dependency>

2.写实现类AES

package com.chwl.medical.crypto.wx;
 
import java.security.AlgorithmParameters;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.Security;
 
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
 
/**
 * AES加密
 * @author liuyazhuang
 *
 */
public class AES {
	
	public static boolean initialized = false;
 
	/**
	 * AES解密
	 * 
	 * @param content
	 *            密文
	 * @return
	 * @throws InvalidAlgorithmParameterException
	 * @throws NoSuchProviderException
	 */
	public byte[] decrypt(byte[] content, byte[] keyByte, byte[] ivByte) throws InvalidAlgorithmParameterException {
		initialize();
		try {
			Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
			Key sKeySpec = new SecretKeySpec(keyByte, "AES");
			cipher.init(Cipher.DECRYPT_MODE, sKeySpec, generateIV(ivByte));// 初始化
			byte[] result = cipher.doFinal(content);
			return result;
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		} catch (NoSuchPaddingException e) {
			e.printStackTrace();
		} catch (InvalidKeyException e) {
			e.printStackTrace();
		} catch (IllegalBlockSizeException e) {
			e.printStackTrace();
		} catch (BadPaddingException e) {
			e.printStackTrace();
		} catch (NoSuchProviderException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
	}
 
	public static void initialize() {
		if (initialized)
			return;
		Security.addProvider(new BouncyCastleProvider());
		initialized = true;
	}
 
	// 生成iv
	public static AlgorithmParameters generateIV(byte[] iv) throws Exception {
		AlgorithmParameters params = AlgorithmParameters.getInstance("AES");
		params.init(new IvParameterSpec(iv));
		return params;
	}
}

3.编写实现WxPKCS7Encoder类

package com.chwl.medical.crypto.wx;
 
import java.nio.charset.Charset;
import java.util.Arrays;
 
 
/**
 * 微信小程序加解密
 * @author liuyazhuang
 *
 */
public class WxPKCS7Encoder {
	private static final Charset CHARSET = Charset.forName("utf-8");
	private static final int BLOCK_SIZE = 32;
 
	/**
	 * 获得对明文进行补位填充的字节.
	 *
	 * @param count
	 *            需要进行填充补位操作的明文字节个数
	 * @return 补齐用的字节数组
	 */
	public static byte[] encode(int count) {
		// 计算需要填充的位数
		int amountToPad = BLOCK_SIZE - (count % BLOCK_SIZE);
		if (amountToPad == 0) {
			amountToPad = BLOCK_SIZE;
		}
		// 获得补位所用的字符
		char padChr = chr(amountToPad);
		String tmp = new String();
		for (int index = 0; index < amountToPad; index++) {
			tmp += padChr;
		}
		return tmp.getBytes(CHARSET);
	}
 
	/**
	 * 删除解密后明文的补位字符
	 *
	 * @param decrypted
	 *            解密后的明文
	 * @return 删除补位字符后的明文
	 */
	public static byte[] decode(byte[] decrypted) {
		int pad = decrypted[decrypted.length - 1];
		if (pad < 1 || pad > 32) {
			pad = 0;
		}
		return Arrays.copyOfRange(decrypted, 0, decrypted.length - pad);
	}
 
	/**
	 * 将数字转化成ASCII码对应的字符，用于对明文进行补码
	 *
	 * @param a
	 *            需要转化的数字
	 * @return 转化得到的字符
	 */
	public static char chr(int a) {
		byte target = (byte) (a & 0xFF);
		return (char) target;
	}
}

4.编写实现WXCore类（这个类主要是对具体算法的封装，统一对外提供方法。

package com.chwl.medical.crypto.wx;
 
import org.apache.commons.codec.binary.Base64;
 
import net.sf.json.JSONObject;
 
 
/**
 * 封装对外访问方法
 * @author liuyazhuang
 *
 */
public class WXCore {
	
	private static final String WATERMARK = "watermark";
	private static final String APPID = "appid";
	/**
	 * 解密数据
	 * @return
	 * @throws Exception
	 */
	public static String decrypt(String appId, String encryptedData, String sessionKey, String iv){
		String result = "";
		try {
			AES aes = new AES();  
		    byte[] resultByte = aes.decrypt(Base64.decodeBase64(encryptedData), Base64.decodeBase64(sessionKey), Base64.decodeBase64(iv));  
		    if(null != resultByte && resultByte.length > 0){  
		        result = new String(WxPKCS7Encoder.decode(resultByte));  
		    	JSONObject jsonObject = JSONObject.fromObject(result);
		    	String decryptAppid = jsonObject.getJSONObject(WATERMARK).getString(APPID);
		    	if(!appId.equals(decryptAppid)){
		    		result = "";
		    	}
	        }  
		} catch (Exception e) {
			result = "";
			e.printStackTrace();
		}
	    return result;
	}
	
	
	public static void main(String[] args) throws Exception{
	   String appId = "wx4f4bc4dec97d474b";
	   String encryptedData = "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";
	   String sessionKey = "tiihtNczf5v6AKRyjwEUhQ==";
	   String iv = "r7BXXKkLb8qrSNn05n0qiA==";
       System.out.println(decrypt(appId, encryptedData, sessionKey, iv));
    }
}

通过上面的代码就可以获取到openid和unionid，然后就可以通过unionid发送消息给指定用户啦！
亲测可用，有什么不懂得大家提出来一起解决！