简单的session共享的封装

目的

　　session存储在缓存服务器上(各种缓存服务器上均可，本文以memcached为例)，但对开发者来说，他不用关注，只需要调用request.getSession()方法即可获取到session，然后对session的属性进行操作。

面临的问题

　　1. session获取，不是从application的服务器上获取，要从memcached上获取。

　　2. session属性的获取及设置，不是设置到application服务器上，而是操作memcached获取或者设置。

解决问题的方法

　　1. 使用一个HttpServletRequestWrapper的实现类，重写getSession()方法，然后使用filter，来过滤每个请求，使request变为requestWrapper。

　　2. 使用一个HttpSessionAttributeListener的实现类，重写attributeAdded()、attributeRemoved()、attributeReplaced()方法，当属性发生改变时需要通知memcached中的session发生改变

另外：为解决各个异构系统因语言不通可能发生的兼容问题，session以json字符串存储。

具体代码如下：

wrapper类

import java.io.IOException;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpSession;



import org.springframework.util.StringUtils;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.javacodegeeks.util.JacksonMapUtil;
import com.javacodegeeks.util.MemcachedUtil;

public class GetSessionWrapper extends HttpServletRequestWrapper{
    private String sessionId=null;
    public GetSessionWrapper(HttpServletRequest request) {
        super(request);
    }
    public GetSessionWrapper(HttpServletRequest request,String sessionId) {
        super(request);
        this.setSessionId(sessionId);
    }
    
    @Override
    public HttpSession getSession() {
        HttpSession httpSession=super.getSession();
        //id-->sessionId;
        String id="davidwang456";
        String json=MemcachedUtil.getValue(id);
        if(StringUtils.isEmpty(json)){
            return httpSession;
        }
        httpSession.setAttribute("JPHPSESSID", id);
        // 读取JSON数据
        Map<String, Object> userData;
        try {
            userData = JacksonMapUtil.getMapper().readValue(json, Map.class);
            for(Map.Entry<String, Object> entry:userData.entrySet()){ 
                httpSession.setAttribute(entry.getKey(), entry.getValue());    
           } 
        } catch (JsonParseException e) {
            System.out.println("json字符串不能解析成功！");
        } catch (JsonMappingException e) {
            System.out.println("json字符串不能映射到Map！");
        } catch (IOException e) {
            System.out.println("io异常！");
        }
        return httpSession;
    }

    @Override
    public HttpSession getSession(boolean create) {
        HttpSession httpSession=super.getSession(create);
        return httpSession;        
    }
    public static void main(String[] args) {
        String sessionId="davidwang456";
        String json=MemcachedUtil.getValue(sessionId);
        System.out.println(json);
    }
    public String getSessionId() {
        return sessionId;
    }
    public void setSessionId(String sessionId) {
        this.sessionId = sessionId;
    }
}

filter类

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;

import org.springframework.web.util.WebUtils;


public class FetchSession implements javax.servlet.Filter{
    private static final String regex=".*(css|html|ico|html|jpg|jpeg|png|gif|js)";
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }
    
    private static String getSessionId(ServletRequest request){
        HttpServletRequest httpRequest=(HttpServletRequest)request;
        String sessionId="";
        Cookie cookie =WebUtils.getCookie(httpRequest, "PHPSESSID");
        if(cookie!=null){
            return cookie.getValue();
        }
        cookie =WebUtils.getCookie(httpRequest, "JSESSIONID");
        if(cookie!=null){
            sessionId= cookie.getValue();
        }
        return sessionId;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
            String sessionId=getSessionId(request);
            HttpServletRequest httpRequest=(HttpServletRequest)request;    
            String requestedUri=httpRequest.getRequestURL().toString();
            System.out.println(requestedUri);
            if(requestedUri.matches(regex)){
                chain.doFilter(request, response);
                return;
            }
            GetSessionWrapper wrapperRequest=new GetSessionWrapper(httpRequest,sessionId);
            //HttpSession httpSession=wrapperRequest.getSession();
            chain.doFilter(wrapperRequest, response);        
    }
    
    @Override
    public void destroy() {
    }
}

属性监听器

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

import org.springframework.util.StringUtils;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.javacodegeeks.util.JacksonMapUtil;
import com.javacodegeeks.util.MemcachedUtil;

public class MySessionAttributeListener 
        implements HttpSessionAttributeListener {
    private static AtomicInteger count=new AtomicInteger(0);
    private static AtomicInteger countU=new AtomicInteger(0);

    @Override
    public void attributeAdded(HttpSessionBindingEvent event) {
        int ss=count.incrementAndGet();
        HttpSession session=event.getSession();
        //String sessionId=(String) session.getAttribute("JPHPSESSID");
        String sessionId="davidwang456";
        String attributeName = event.getName();
        Object attributeValue = event.getValue();
        System.out.println("Attribute add " + attributeName + " : " + attributeValue+",ss="+ss);
        String json=MemcachedUtil.getValue(sessionId);
        if(StringUtils.isEmpty(json)){
            return ;
        }
        String json_new;
        try {
            json_new = attributeAddOrUpdate(json,attributeName,attributeValue);
            MemcachedUtil.setValue(sessionId, json_new);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    private String attributeAddOrUpdate(String json,String key,Object value) 
                            throws JsonParseException, JsonMappingException, IOException{
        ObjectMapper mapper=JacksonMapUtil.getMapper();
        @SuppressWarnings("unchecked")
        Map<String,Object> userData = mapper.readValue(json, Map.class);
        Boolean flag=String.class.isAssignableFrom(value.getClass());
        if(!flag){
            Map<String, Object> map = mapper.convertValue(value, Map.class);
            userData.putAll(map);
        }else{
            userData.put(key, value);
        }      
        return mapper.writeValueAsString(userData); 
    }
    
    private String attributeDel(String json, String key)
            throws JsonParseException, JsonMappingException, IOException {
        ObjectMapper mapper = JacksonMapUtil.getMapper();
        @SuppressWarnings("unchecked")
        Map<String, Object> userData = mapper.readValue(json, Map.class);
        userData.remove(key);
        return mapper.writeValueAsString(userData);
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent event) {
        HttpSession session=event.getSession();
        //String sessionId=(String) session.getAttribute("JPHPSESSID");
        String sessionId="davidwang456";
        String attributeName = event.getName();
        System.out.println("Attribute del : " + attributeName);
        String json=MemcachedUtil.getValue(sessionId);
        if(StringUtils.isEmpty(json)){
            return ;
        }
        String json_new;
        try {
            json_new = attributeDel(json,attributeName);
            MemcachedUtil.setValue(sessionId, json_new);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent event) {

        int ssu=countU.incrementAndGet();
        HttpSession session=event.getSession();
        //String sessionId=(String) session.getAttribute("JPHPSESSID");
        String sessionId="davidwang456";
        String attributeName = event.getName();
        Object attributeValue = event.getValue();
        System.out.println("Attribute update " + attributeName + " : " + attributeValue+",ss="+ssu);
        String json=MemcachedUtil.getValue(sessionId);
        if(StringUtils.isEmpty(json)){
            return ;
        }
        String json_new;
        try {
            json_new = attributeAddOrUpdate(json,attributeName,attributeValue);
            MemcachedUtil.setValue(sessionId, json_new);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    
    }

}

pom.xml依赖：

<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.4.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.4.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-guava</artifactId>
            <version>2.4.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-joda</artifactId>
            <version>2.4.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
            <version>2.4.3</version>
        </dependency>
        <dependency>
            <groupId>net.spy</groupId>
            <artifactId>spymemcached</artifactId>
            <version>2.12.0</version>
        </dependency>

注意：上面代码仅为demo代码，实际应用需重构代码。