Filter常见应用(五)---缓存数据到内存

有些页面，其内容很就才会改变，大多数时间是不变的，对这些内容我们可以做些处理，使其不要每次都去服务器端获取数据，这样可以优化服务器的性能，减少服务器的压力。这些内容可以将其缓存下来。原理是添加一个过滤器，此过滤器负责将这些内容缓存到内存中或者文件中，待下次在访问此资源时，就直接从缓存中或内存中取出，直接返回给浏览器。

要实现此功能呢，具体步骤如下：

1、过滤器负责建一个map容器，负责缓存这些静态数据。其key值为资源的请求URI,值为资源返回的数据

2、获取一个请求的URI

3、要是此URI资源在这个缓存中map集合中，则直接从此集合中取出此数据，写给浏览器

4、要是不在URI中，则放行

5、获取URI请求资源的数据，添加到map容器中，key值为此资源的URI值

6、将此数据写给浏览器

下面则是具体的code:

public class MyCacheFilter implements Filter {
	private HashMap<String, byte[]> map = new HashMap<String, byte[]>();
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		// TODO Auto-generated method stub

	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse resp,
			FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		
		HttpServletRequest request = (HttpServletRequest)req;
		HttpServletResponse response = (HttpServletResponse)resp;
		//1.获取资源URI, 作为Map集合的key
		String uri = request.getRequestURI();
		//2.要是map中有，则从map集合中取出其内容
		byte[] buf = map.get(uri);
		if(buf!=null){
			response.getOutputStream().write(buf);
			return;
		}
		//3.放行并获取其内容
		MyCompressResponse myResp = new MyCompressResponse(response);
		chain.doFilter(request, myResp);
		byte[] out = myResp.getBuffer();
		
		//4.将其写入到map集合中
		map.put(uri, out);
		
		//5.将其写入到浏览器中
		response.getOutputStream().write(out);
		
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}

}

将数据先写到缓存中

public class MyCompressResponse extends HttpServletResponseWrapper {
	private HttpServletResponse response;
	private ByteArrayOutputStream bout = new ByteArrayOutputStream();
	private PrintWriter pw;
	
	public MyCompressResponse(HttpServletResponse response) {
		super(response);
		// TODO Auto-generated constructor stub
		this.response = response;
	}

	/* (non-Javadoc)
	 * @see javax.servlet.ServletResponseWrapper#getOutputStream()
	 */
	@Override
	public ServletOutputStream getOutputStream() throws IOException {
		// TODO Auto-generated method stub
		return new MyOutputStream(bout);
	}


	@Override
	public PrintWriter getWriter() throws IOException {
		// TODO Auto-generated method stub
		pw =  new MyPrintWriter(bout, super.getCharacterEncoding());
		
		return pw;
	}
	
	public byte[] getBuffer(){
		if(pw!=null){
			pw.close();
			
		}
		if(bout!=null){
			return bout.toByteArray();
		}
		
		return null;
	}

	/* (non-Javadoc)
	 * @see javax.servlet.ServletResponseWrapper#getWriter()
	 */
	
}

class MyOutputStream extends ServletOutputStream{
	private ByteArrayOutputStream bout;
	
	
	@Override
	public void write(int b) throws IOException {
		// TODO Auto-generated method stub
		bout.write(b);
	}
	
	public MyOutputStream(ByteArrayOutputStream bout){
		this.bout = bout;
		
	}
	
}

class MyPrintWriter extends PrintWriter{
	private  ByteArrayOutputStream bout;
	private String charset;
	
	public MyPrintWriter(ByteArrayOutputStream bout, String charset) {
		super(bout);
		// TODO Auto-generated constructor stub
		this.bout = bout;
		this.charset = charset;
	}

	/* (non-Javadoc)
	 * @see java.io.PrintWriter#write(java.lang.String)
	 */
	@Override
	public void write(String s) {
		// TODO Auto-generated method stub
		try {
			bout.write(s.getBytes(charset));
		} catch (UnsupportedEncodingException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
}