/**
 * 微信请求处理的核心类
 */
public class CoreServlet extends HttpServlet 
{
	private static final long serialVersionUID = 4440739483644821986L;

	/**
	 * 请求校验（确认请求来自微信服务器）
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
	{
		// 微信服务端发来的加密签名
		String signature = request.getParameter("signature");
		// 时间戳
		String timestamp = request.getParameter("timestamp");
		// 随机数
		String nonce = request.getParameter("nonce");
		// 随机字符串
		String echostr = request.getParameter("echostr");
		
		PrintWriter out = response.getWriter();
		// 请求校验，若校验成功则原样返回echostr，表示接入成功，否则接入失败
		if (SignUtil.checkSignature(signature, timestamp, nonce)) {
			out.print(echostr);
		}
		out.close();
	
	}

package com.sinaapp.wx.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

import com.sinaapp.wx.config.ParameterConfig;

/**
 * 请求校验工具类
 */
public class SignUtil {
	/**
	 * 校验签名
	 * 
	 * @param signature 微信加密签名
	 * @param timestamp 时间
	 * @param nonce 随机字符串
	 * @return
	 */
	public static boolean checkSignature(String signature, String timestamp, String nonce) {
		String token = ParameterConfig.WX_TOKEN;
		String[] paramArr = new String[] { token, timestamp, nonce };
		Arrays.sort(paramArr);	// 对token、timestamp和nonce按字典排序

		// 将排序后的结果拼接成字符串
		StringBuilder sb = new StringBuilder(paramArr[0]);
		sb.append(paramArr[1]);
		sb.append(paramArr[2]);

		String cipherText = null;
		try {
			MessageDigest md = MessageDigest.getInstance("SHA-1");
			byte[] digest = md.digest(sb.toString().getBytes());	// 对接后的字符串进行sha1加密
			cipherText = byteToStr(digest);
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		
		// 将加密后的字符串与微信服务器发来的签名signature进行对比
		return cipherText != null ? cipherText.equals(signature.toUpperCase()) : false;
	}

	/**
	 * 将字节数组转换为十六进制字符
	 * 
	 * @param byteArray
	 * @return
	 */
	private static String byteToStr(byte[] byteArray) {
		String strDigest = "";
		for (int i = 0; i < byteArray.length; i++) {
			strDigest += byteToHexStr(byteArray[i]);
		}
		return strDigest;
	}

	/**
	 * 将单个字节转换为十六进制字符
	 * 
	 * @param mByte
	 * @return
	 */
	private static String byteToHexStr(byte mByte) {
		char[] Digit = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
		char[] tempArr = new char[2];
		tempArr[0] = Digit[(mByte >>> 4) & 0X0F];	// 取一个字节的高4位，然后获得其对应的十六进制字符
		tempArr[1] = Digit[mByte & 0X0F];	//  取一个字节的低4位，然后获得其对应的十六进制字符  

		return new String(tempArr);
		
	}
}
 代码中String token = ParameterConfig.WX_TOKEN的值必须和上面填写的Token一致。在web.xml中配置该servlet：

  <servlet>
  	<servlet-name>coreServlet</servlet-name>
  	<servlet-class>com.sinaapp.wx.servlet.CoreServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>coreServlet</servlet-name>
  	<url-pattern>/coreServlet</url-pattern>
  </servlet-mapping>