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[1]jquery ajax 与servlet间乱码解决方案

中文乱码问题，解决办法其实很简单，传之前encode，传之后decode。看相关源码片段：

servlet

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		request.setCharacterEncoding("UTF-8");
		PrintWriter pw = response.getWriter();
		String userId = request.getParameter("userId");
		String vcard = VcardHandle.queryVcard(userId);
		pw.print(URLEncoder.encode(vcard, "UTF-8"));
		pw.close();
	}

JavaScript

	$.ajax({
		type : "POST",
		contentType : "application/x-www-form-urlencoded; charset=utf-8",
		async : false,
		url : "VcardServlet?userId=" + userId,
		dataType : 'text',
		success : function(result) {
			vcard = decodeURIComponent(result);
		}
	});

需要注意的是：JavaScript中encodeURI 不对下列字符进行编码：“:”、“/”、“;”和“?”，建议使用encodeURIComponent 

dml@2013.1.8

[2]String,StringBuffer,StringBuilder的性能比较

首先看多次相加

String 循环10000次，后两者是100000，累加次数是String的10倍

		long start = System.currentTimeMillis();
		String result = "";
		for (int i = 0; i < 10000; i++) {
			String s1 = "hello";
			String s2 = "world";
			int s3 = 1000;
			result += s1;
			result += s2;
			result += s3;
		}
		System.out.println(System.currentTimeMillis() - start);
		
		
		start = System.currentTimeMillis();
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 100000; i++) {
			String s1 = "hello";
			String s2 = "world";
			int s3 = 1000;
			sb.append(s1);
			sb.append(s2);
			sb.append(s3);
				
		}
		sb.toString();
		System.out.println(System.currentTimeMillis() - start);
		
		
		start = System.currentTimeMillis();
		StringBuffer sb2 = new StringBuffer();
		for (int i = 0; i < 100000; i++) {
			String s1 = "hello";
			String s2 = "world";
			int s3 = 1000;
			sb2.append(s1);
			sb2.append(s2);
			sb2.append(s3);
				
		}
		sb2.toString();
		System.out.println(System.currentTimeMillis() - start);

看下运行时间

结果是：

7549
36
33

比较稳定

6687
34
31

实际情况是，我们很少会对一个字符串累加那么多次吧！上百次应该都很少。

这是就先累加10次（内循环10次累加），但必须要循环执行多次（外循环）才能看出效果！这里循环10W次。，都一样。

		long start = System.currentTimeMillis();
		String s = "hello world";
		for (int i = 0; i < 100000; i++) {
			String result = "";
			for(int j=0; j<10; j++){
				result += s;
			}
		}
		System.out.println(System.currentTimeMillis() - start);
		
		
		start = System.currentTimeMillis();
		
		for (int i = 0; i < 100000; i++) {
			StringBuilder sb = new StringBuilder();
			for(int j=0; j<10; j++){
				sb.append(s);
			}
			sb.toString();
		}
		
		System.out.println(System.currentTimeMillis() - start);
		
		
		start = System.currentTimeMillis();
		
		for (int i = 0; i < 100000; i++) {
			StringBuffer sb2 = new StringBuffer();
			for(int j=0; j<10; j++){
				sb2.append(s);
			}
			sb2.toString();
		}
		
		System.out.println(System.currentTimeMillis() - start);

结果为：

304
88
117

如果，把累加次数改为20次（内循环，j<20）

806
164
209

30次， 性能提升还是比较大的。（当然是在循环10W的基础上）

1397
275
483

想起来以来看过的一篇帖子，比较的JSP和PHP运算字符串的能力。

看结果就知道用的是String累加的！这种比较没意思！

[3]下载文件

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;


import javax.servlet.http.HttpServletResponse;


import org.apache.log4j.Logger;


public class DownLoadUtil {
	private static Logger logger = Logger.getLogger(DownLoadUtil.class);
	/**
	 * 下载文件
	 * @param name 用户下载的文件名(*****.***)
	 * @param filePath 文件路径
	 * @param response 
	 * @param fileType 文件类型
	 * @return
	 * @throws Exception
	 */
	public static boolean downLoadFile(String name,String filePath,
			HttpServletResponse response, String fileType)
			throws Exception {
		logger.info("start invoke downLoadFile,[filePath:"+filePath+" , fileType:"+fileType+"]");
		File file = new File(filePath);
		//设置文件类型
		if("pdf".equals(fileType)){
			response.setContentType("application/pdf");
		}else if("xls".equals(fileType)){
			response.setContentType("application/msexcel");
		}else if("doc".equals(fileType)){
			response.setContentType("application/msword");
		}
		response.setHeader("Content-Disposition", "attachment;filename=\""
				+ new String(name.getBytes("GB2312"), "ISO8859-1") + "\"");
		//response.setHeader("Content-Disposition", "attachment;filename=\""+ URLEncoder.encode(name, "UTF-8")+ "\"");
		response.setContentLength((int) file.length());
		byte[] buffer = new byte[4096];// 缓冲区
		BufferedOutputStream output = null;
		BufferedInputStream input = null;
		try {
			output = new BufferedOutputStream(response.getOutputStream());
			input = new BufferedInputStream(new FileInputStream(file));
			int n = -1;
			while ((n = input.read(buffer, 0, 4096)) > -1) {
				output.write(buffer, 0, n);
			}
			output.flush();
			response.flushBuffer();
		} catch (Exception e) {
			logger.error("exception when invoke downLoadFile",e);
			throw e;
		} finally {
			if (input != null)
				input.close();
			if (output != null)
				output.close();
		}
		logger.info("end invoke downLoadFile!");
		return true;
	}
}

 

   

调用 DownLoadUtil.java

 

public ActionForward downLoadExcelModel(ActionMapping actionMapping,
   ActionForm actionForm, HttpServletRequest request,
   HttpServletResponse response) throws Exception {
  String busType = request.getParameter("busType");
  String path = request.getSession().getServletContext().getRealPath(
    "/resources");
  String name = null;        
  String fileName = null;    //服务器上文件名
    fileName = "xxxl.xls";
    name = "xxxx.xls";
  }
  String filePath = path + System.getProperty("file.separator") + fileName;
  DownLoadUtil.downLoadFile(name,filePath, response, "xls");
  return null;
 }