拦截请求返回值的方法

ゝ一世哀愁。 2022-07-15 07:43 665阅读 0赞

在web应用开发时，我们经常会需要拦截请求，在请求前后做一些事，比如打印日志等，这种方式就相当于spring中的面向切面编程，以下总结了下实现这种方式的一些方法。

\#\#\#1. 使用拦截器+过滤器

这种方法是目前比较通用的方法，不受限于框架限制，不管是用SSH还是springmvc都可以采用，实现方式大致如下：  
（1）定义一个拦截器，比如WebRequestInterceptor，在preHandle里面拦截request，从中取出参数等信息，然后打印出来即可。  
（2）定义一个过滤器，比如WebResponseFilter，在doFilter里面使用HttpServletResponseWrapper包装传进来的response，然后重写一些方法即可实现。  
（注意：这里有个坑，就是直接使用拦截器无法从response里面取出返回值！）  
（3）相关代码大致如下：

WebInterceptor.java

package com.zuolin.interceptor;
    
    import java.util.Enumeration;
    
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.web.servlet.HandlerInterceptor;
    import org.springframework.web.servlet.ModelAndView;
    
    import com.zuolin.filter.WrapperResponse;
    
    public class WebInterceptor implements HandlerInterceptor {
    
    	private static final Logger logger = LoggerFactory.getLogger(WebInterceptor.class);
    
    	@Override
    	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object object) throws Exception {
    		if (logger.isDebugEnabled()) {
    
    			StringBuffer sb = new StringBuffer();
    			sb.append("{");
    
    			Enumeration<String> headers = request.getHeaderNames();
    			int i = 0;
    			while (headers.hasMoreElements()) {
    				String header = headers.nextElement();
    
    				if (i > 0)
    					sb.append(", ");
    				sb.append(header + ": " + request.getHeader(header));
    				i++;
    			}
    			sb.append("}");
    
    			logger.debug("Pre handling request: {}, headers: {}", getRequestInfo(request, true), sb.toString());
    		}
    		
    		return true;
    	}
    
    	private static String getRequestInfo(HttpServletRequest request, boolean requestDetails) {
    		StringBuffer sb = new StringBuffer();
    		sb.append(request.getMethod()).append(" ");
    		sb.append(request.getRequestURI());
    		if (requestDetails) {
    			Enumeration<String> e = request.getParameterNames();
    			sb.append("{");
    			int i = 0;
    			while (e.hasMoreElements()) {
    				String name = e.nextElement();
    				String val = request.getParameter(name);
    
    				if (val != null && !val.isEmpty()) {
    					if (i > 0)
    						sb.append(", ");
    					sb.append(name).append(": ").append(val);
    
    					i++;
    				}
    			}
    			sb.append("}");
    		}
    
    		return sb.toString();
    	}
    
    	@Override
    	public void postHandle(HttpServletRequest request, HttpServletResponse response, Object object,
    			ModelAndView modelAndView) throws Exception {
    	}
    
    	@Override
    	public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object object,
    			Exception exception) throws Exception {
    		String requestInfo = getRequestInfo(request, false);
    		if (logger.isDebugEnabled()) {
    			logger.debug("Complete request: {}", requestInfo);
    		}
    	}
    }

WrapperOutputStream.java

package com.zuolin.filter;
    
    import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    
    import javax.servlet.ServletOutputStream;
    
    public class WrapperOutputStream extends ServletOutputStream{
    	private ByteArrayOutputStream bos;
    	
    	public WrapperOutputStream(ByteArrayOutputStream bos) {
    		this.bos = bos;
    	}
    	
    	@Override
    	public void write(int b) throws IOException {
    		bos.write(b);
    	}
    }

WrapperResponse.java

package com.zuolin.filter;
    
    import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    import java.io.OutputStreamWriter;
    import java.io.PrintWriter;
    import java.io.UnsupportedEncodingException;
    
    import javax.servlet.ServletOutputStream;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpServletResponseWrapper;
    
    public class WrapperResponse extends HttpServletResponseWrapper{
    	private ByteArrayOutputStream buffer;
    	private ServletOutputStream out;
    	
    	public WrapperResponse(HttpServletResponse response) throws UnsupportedEncodingException {
    		super(response);
    		buffer = new ByteArrayOutputStream();
    		out = new WrapperOutputStream(buffer);
    	}
    
    	@Override
    	public ServletOutputStream getOutputStream() throws IOException {
    		return out;
    	}
    	
    	@Override
    	public void flushBuffer() throws IOException {
    		if (out != null) {
    			out.flush();
    		}
    	}
    	
    	public byte[] getContent() throws IOException {
    		flushBuffer();
    		return buffer.toByteArray();
    	}
    }

ResponseFilter.java

package com.zuolin.filter;
    
    import java.io.IOException;
    
    import javax.servlet.Filter;
    import javax.servlet.FilterChain;
    import javax.servlet.FilterConfig;
    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.http.HttpServletResponse;
    
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    
    public class ResponseFilter implements Filter {
    	private static final Logger logger = LoggerFactory.getLogger(ResponseFilter.class);
    	
    	@Override
    	public void destroy() {
    	}
    
    	@Override
    	public void doFilter(ServletRequest request, ServletResponse response,
    			FilterChain filterChain) throws IOException, ServletException {
    		WrapperResponse wrapperResponse = new WrapperResponse((HttpServletResponse) response);
    		filterChain.doFilter(request, wrapperResponse);
    		byte[] content = wrapperResponse.getContent();
    		if (logger.isDebugEnabled() && content != null && content.length > 0) {
    			logger.debug("Response Content: {}", new String(content));
    		}
    		ServletOutputStream out = response.getOutputStream();
    		out.write(content);
    		out.flush();
    	}
    
    	@Override
    	public void init(FilterConfig paramFilterConfig) throws ServletException {
    	}
    
    }

然后记得在web.xml或spring的配置文件中加上以上类的定义就可以直接使用了。

这种方式有个缺陷，就是要写很多代码，而且一般人看不懂这里的流程，因为使用的是流。

\#\#\#2. 使用spring中的advice

这种就是spring里面的面向切面编程的使用了，这种方式只能依赖于spring的aspect存在，实现方法为：  
（1）声明一个类，比如叫WebRequestAroundAdvice；  
（2）定义切入点；  
（3）定义切入点的处理方法。  
（4）相关代码如下：

WebRequestAroundAdvice.java

package com.zuolin.interceptor;
    
    import java.util.Enumeration;
    
    import javax.servlet.http.HttpServletRequest;
    
    import org.aspectj.lang.ProceedingJoinPoint;
    import org.aspectj.lang.annotation.Around;
    import org.aspectj.lang.annotation.Aspect;
    import org.aspectj.lang.annotation.Pointcut;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.web.context.request.RequestContextHolder;
    import org.springframework.web.context.request.ServletRequestAttributes;
    
    import com.alibaba.fastjson.JSONObject;
    
    @Aspect
    public class WebRequestAroundAdvice {
    	private static final Logger logger = LoggerFactory.getLogger(WebRequestAroundAdvice.class);
    	
    	@Pointcut( value = "execution(* com.zuolin.controller.*.*(..))" )
    	public void pointcut(){}
    	
    	@Around("pointcut()")
    	public Object handle(ProceedingJoinPoint joinPoint) throws Throwable{
    		preHandle();
    		
    		Object retVal = joinPoint.proceed();
    		
    		postHandle(retVal);
    		
    		return retVal;
    	}
    	
    	
    	private void preHandle() {
    		if (logger.isDebugEnabled()) {
    			HttpServletRequest request = ( (ServletRequestAttributes) RequestContextHolder.getRequestAttributes() ).getRequest();
    
    			StringBuffer sb = new StringBuffer();
    			sb.append("{");
    
    			Enumeration<String> headers = request.getHeaderNames();
    			int i = 0;
    			while (headers.hasMoreElements()) {
    				String header = headers.nextElement();
    
    				if (i > 0)
    					sb.append(", ");
    				sb.append(header + ": " + request.getHeader(header));
    				i++;
    			}
    			sb.append("}");
    
    			logger.debug("Pre handling request: {}, headers: {}", getRequestInfo(request, true), sb.toString());
    		}
    	}
    
    	private void postHandle(Object retVal) {
    		if (logger.isDebugEnabled()) {
    			HttpServletRequest request = ( (ServletRequestAttributes) RequestContextHolder.getRequestAttributes() ).getRequest();
    			logger.debug("Post handling request: {}, response: {}", getRequestInfo(request, false), JSONObject.toJSONString(retVal));
    		}
    	}
    
    	private String getRequestInfo(HttpServletRequest request, boolean requestDetails) {
    		StringBuffer sb = new StringBuffer();
    		sb.append(request.getMethod()).append(" ");
    		sb.append(request.getRequestURI());
    		if (requestDetails) {
    			Enumeration<String> e = request.getParameterNames();
    			sb.append(" ").append("{");
    			int i = 0;
    			while (e.hasMoreElements()) {
    				String name = e.nextElement();
    				String val = request.getParameter(name);
    
    				if (val != null && !val.isEmpty()) {
    					if (i > 0)
    						sb.append(", ");
    					sb.append(name).append(": ").append(val);
    
    					i++;
    				}
    			}
    			sb.append("}");
    		}
    
    		return sb.toString();
    	}
    }

然后在spring的配置文件中配置这个bean就可以直接使用了。

这种方式的优点就是代码很简洁，只要稍微学过一点AOP都能很容易理解，缺点就是依赖于spring。

这里只使用了spring的around advice，当然，使用其它的几种advice的组合也可以实现相同的效果，或者混合使用拦截器和advice也可以，关键在于你。

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