解决servlet调用spring中bean的问题
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Java

500 字
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2 分钟

前段时间开发了一个web小系统，主要是和.net客户端交互，由于不是很复杂，就没有采用webservice，而是使用了HttpCLient通过json方式交互，在交互的时候想在servlet中直接调用spring的bean，这样能节省不少时间。但是直接调用总是报错，网上查了一下才知道，servlet是无法直接调用spring中的bean的，如果直接调用，一般都会报空指针异常。

为什么会这样？其实我们使用spring的目的就是为了让spring为我们来提供一个已经被注入好的一个实例。而servlet是不同的，servlet是有生命周期的，而这个并不归属spring管理，而是由web容器管理的。那么当servlet刚刚创建的时候，spring可以为servlet注入，当你访问的时候，由于servlet是单实例多线程的，所以，servlet信息被重置，刚刚被注入的对象又为null了。

那么该怎么处理这个问题呢？其实只要我在获得servlet的时候，用从Spring获得，而不是由web容器获得就可以了。而解决这个方法的思路就是，我们使用一个代理的servlet，利用这个代理的servlet去调用我们的业务servlet（其中这个业务servlet是被配置为spring中的bean），这样就可以实现其他bean注入，然后使用代理servlet调用。

首先看代理Servlet代码


import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

public class HttpServletProxy extends HttpServlet {
 /**
 * random serialVersionUID
 */
 private static final long serialVersionUID = -7208519469035631940L;
 private static Logger logger = LoggerFactory
 .getLogger(HttpServletProxy.class);
 private String targetServlet;
 private HttpServlet proxy;
 public void init() throws ServletException {
 this.targetServlet = getInitParameter("targetServlet");
 getServletBean();
 proxy.init(getServletConfig());
 System.out.println(targetServlet + " was inited by HttpServletProxy successfully......");
 }
 private void getServletBean() {
 WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
 this.proxy = (HttpServlet) wac.getBean(targetServlet);
 }
 @Override
 public void service(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException, RuntimeException {
 proxy.service(request, response);
 }

}

接下来看我们使用的业务Servlet的代码：

import java.io.IOException;
import java.io.PrintWriter;
import java.math.BigDecimal;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;

import com.qdhh.xfylxt.bean.Ygxxbean;
import com.qdhh.xfylxt.common.bean.Pager;
import com.qdhh.xfylxt.entity.XFTrainSetting;
import com.qdhh.xfylxt.entity.XFYgtrainScore;
import com.qdhh.xfylxt.entity.XFYgxx;
import com.qdhh.xfylxt.entity.XFZksxx;
import com.qdhh.xfylxt.service.XFTrainService;
import com.qdhh.xfylxt.service.XFYgxxService;
import com.qdhh.xfylxt.service.XFZksxxService;

@Component
public class RemoteServlet extends HttpServlet {
 /**
 * Constructor of the object.
 */
 public RemoteServlet() {
 super();
 }

 @Autowired
 private XFTrainService xFTrainService;
 @Autowired
 private XFYgxxService xFYgxxService;
 @Autowired
 private XFZksxxService xFZksxxService;

 /**
 * Destruction of the servlet. <br>
 */
 public void destroy() {
 super.destroy(); // Just puts "destroy" string in log
 }

 /**
 * The doGet method of the servlet. <br>
 *
 * This method is called when a form has its tag value method equals to get.
 *
 * @param request
 * the request send by the client to the server
 * @param response
 * the response send by the server to the client
 * @throws ServletException
 * if an error occurred
 * @throws IOException
 * if an error occurred
 */
 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 String method = request.getParameter("method");
 if(Utils.isEmpty(method)){
 return;
 }
 System.out.println(request.getQueryString());
 response.setContentType("text/html" + ";charset=UTF-8");
 response.setHeader("Pragma", "No-cache");
 response.setHeader("Cache-Control", "no-cache");
 response.setDateHeader("Expires", 0);
 String zksbh = request.getParameter("zksbh");
 XFZksxx zksxxSearch = new XFZksxx();
 zksxxSearch.setZksbh(zksbh);
 Pager page = xFZksxxService.queryPageByCxtj(zksxxSearch, 0, 20);
 XFZksxx zksxx = (XFZksxx)page.getList().get(0);
 PrintWriter out = response.getWriter();
 String result = "";
 if(zksxx == null) {
 result = handlerSuccess("服务器端无此中控室，请检查后重新连接");
 } else {
 if("queryTrainSetting".equals(method)) { // 根据中控室下载考核内容设置

 XFTrainSetting ts = xFTrainService.getTrainSetting(zksbh);
 Map<String, Object> map = new HashMap<String, Object>();
 if(ts != null) {
 List zdylxt = ts.queryZdylxtList();
 List zdyyss = ts.queryZdylssList();
 String s1 = StringUtils.collectionToDelimitedString(zdylxt, "");
 String s2 = StringUtils.collectionToDelimitedString(zdyyss, "");
 System.out.println(s1);
 System.out.println(s2);
 map.put("zdylxt", s1);
 map.put("zdyyss", s2);
 } else {
 map.put("zdylxt", "00000000");
 map.put("zdyyss", "00000000000");
 }
 JSONObject jsonObject = JSONObject.fromObject(map);
 result = jsonObject.toString();

 } else if("downYgxx".equals(method)) { // 根据中控室下载员工信息
 XFYgxx search = new XFYgxx();
 search.setZksbh(zksbh);
 List<XFYgxx> list = xFYgxxService.queryAll(search);
 List<Ygxxbean> ygList = new ArrayList<Ygxxbean>();
 if(!Utils.isEmpty(list)) {
 for(XFYgxx yg: list) {
 Ygxxbean bean = new Ygxxbean();
 BeanUtils.copyProperties(yg, bean);
 ygList.add(bean);
 }

 }
 JSONArray json = JSONTools.toJSONArray(ygList);
 result = json.toString();
 } else if("downZksxx".equals(method)) { // 下载所有的中控室信息
 List<XFZksxx> list = xFZksxxService.queryAll();
 JSONArray json = JSONTools.toJSONArray(list);
 result = json.toString();
 } else if("downTrainxx".equals(method)) {
 List<XFYgtrainScore> list = xFTrainService.queryAllTrainScore(null);
 JSONArray json = JSONTools.toJSONArray(list);
 result = json.toString();
 } else if("uploadYgxx".equals(method)){ // 上传员工信息
 String idcard = request.getParameter("idcard");
 String name = request.getParameter("name");
 String username = request.getParameter("username");
 String password = request.getParameter("password");
 String status = request.getParameter("status");
 XFYgxx ygxx = new XFYgxx();
 ygxx.setName(name);
 ygxx.setPassword(password);
 ygxx.setUsername(username);
 ygxx.setIdcard(idcard);
 ygxx.setStatus(status);
 ygxx.setZksbh(zksbh);
 ygxx.setRegtime(new Date());
 ygxx.setZksid(zksxx.getTid());
 ygxx.setZksname(zksxx.getName());
 String msg = xFYgxxService.updateYgxxByClient(ygxx);
 result = handlerSuccess(msg);
 } else if("uploadTrain".equals(method)) { // 上传用户考核成绩
 try {
 String idcard = request.getParameter("idcard");
 String name = request.getParameter("name");
 String starttime = request.getParameter("starttime");
 String duration = request.getParameter("duration");
 String grades = request.getParameter("grade");

 Double temp = Double.parseDouble(grades);
 BigDecimal bg = new BigDecimal(temp);
 double grade = bg.setScale(2, BigDecimal.ROUND_CEILING).doubleValue();

 XFYgtrainScore trainScore= new XFYgtrainScore();
 Date kssj = TimeUtil.toUtilDateFromStrDateByFormat(starttime,"yyyy-MM-dd hh:mm:ss");
 trainScore.setIdcard(idcard);
 trainScore.setStartTime(kssj);
 trainScore.setName(name);
 trainScore.setTimeSpan(duration);
 trainScore.setGrade(grade);
 trainScore.setZksid(zksxx.getTid());
 trainScore.setZksbh(zksbh);
 trainScore.setZksname(zksxx.getName());
 xFTrainService.uploadTrainScore(trainScore);
 result = handlerSuccess("操作成功");
 } catch (NumberFormatException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 } catch (ParseException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }

 } else if("downloadUserGrade".equals(method)) { // 下载指定用户成绩
 String idcard = request.getParameter("idcard");
 XFYgtrainScore scoreSearch = new XFYgtrainScore();
 scoreSearch.setIdcard(idcard);
 List<XFYgtrainScore> list = xFTrainService.queryAllTrainScore(scoreSearch);
 JSONArray json = JSONTools.toJSONArray(list);
 result = json.toString();

 } else if("downloadAllGrade".equals(method)) { // 下载所有用户的成绩
 XFYgtrainScore scoreSearch = new XFYgtrainScore();
 scoreSearch.setZksbh(zksbh);
 List<XFYgtrainScore> list = xFTrainService.queryAllTrainScore(scoreSearch);
 JSONArray json = JSONTools.toJSONArray(list);
 result = json.toString();
 System.out.println(result);
 } else if("uploadYgmm".equals(method)) { // 更改用户密码
 String idcard = request.getParameter("idcard");
 String password = request.getParameter("password");
 String msg = xFYgxxService.changePassByClient(idcard, password);
 result = handlerSuccess(msg);
 } else if("uploadRysl".equals(method)) { //上传人员数量
 String peracount = request.getParameter("peracount");
 zksxx.setPeracount(Long.parseLong(peracount));
 xFZksxxService.update(zksxx);
 result = handlerSuccess("操作成功");
 }
 }
 out.write(result);
 out.flush();
 }

 public String handlerSuccess(String msg, Object result) {
 Map<String, Object> map = new HashMap<String, Object>();
 map.put("success", true);
 map.put("msg", msg);
 map.put("result", result);
 JSONObject jsonObject = JSONObject.fromObject(map);
 return jsonObject.toString();
 }

 public String handlerSuccess(String msg) {
 return handlerSuccess(msg,null);
 }

 public String handlerSuccess(Object result) {
 return handlerSuccess(null,result);
 }

 /**
 * The doPost method of the servlet. <br>
 *
 * This method is called when a form has its tag value method equals to
 * post.
 *
 *
 * @param request
 * the request send by the client to the server
 * @param response
 * the response send by the server to the client
 * @throws ServletException
 * if an error occurred
 * @throws IOException
 * if an error occurred
 */
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doGet(request, response);
 }

 /**
 * Initialization of the servlet. <br>
 *
 * @throws ServletException
 * if an error occurs
 */
 public void init() throws ServletException {
 // Put your code here
 }

 public XFTrainService getXFTrainService() {
 return xFTrainService;
 }

 public void setXFTrainService(XFTrainService trainService) {
 xFTrainService = trainService;
 }

}

代码就到这了，接下来就需要配置了，
业务serlvet配置为spring的bean:


<bean id="remoteServlet" />

web.xml中业务servlet的配置如下：

<servlet>
 <description>This is the description of my J2EE component</description>
 <display-name>This is the display name of my J2EE component</display-name>
 <servlet-name>RemoteServlet</servlet-name>
 <servlet-class>com.qdhh.xfylxt.util.HttpServletProxy</servlet-class>
 <init-param>
 <param-name>targetServlet</param-name>
 <param-value>remoteServlet</param-value>
 </init-param>
 </servlet>

<servlet-mapping>
 <servlet-name>RemoteServlet</servlet-name>
 <url-pattern>/remote</url-pattern>
 </servlet-mapping>
JavaSpring
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