2021 May 10 Java后端开发

JavaEE开发-第六节 JavaEE项目实战(二)

面向接口编程

  1. 当前的项目目录如下：

     bean
     BaseBean
     Education
     Website
 dao
     EducationDao
     WebsiteDao
 service
     EducationService
     WebsiteService
 servlet
     BaseServlet
     EducationServlet
     WebsiteServlet
  2. 在dao、service文件夹下分别新建文件夹impl
  3. 将所有的dao跟service的类名修改后面全部添加Impl,然后全部拖拽到相应的Impl文件夹中
    1. 比如BaseDao修改为WebsiteDaoImpl
  4. 在dao跟service文件夹下新建每个类的接口，右击new-JavaClass（选择Interface）
    1. 比如在dao下新建BaseDao这个接口
     dao
     impl
         EducationDaoImpl
         WebsiteDaoImpl
     EducationDao
     WebsiteDao
 service
     impl
         EducationServiceImpl
         WebsiteServiceImpl
     EducationService
     WebsiteService
  5. 将Impl类中的方法都抽取到对应的接口中

    1. EducationDao与EducationService一样

       public interface EducationDao {
     boolean remove(Integer id);
     boolean remove(List<Integer> ids);
     boolean save(Education education);
     Education get(Integer id);
     List<Education> list();
     int count();
 }

    2. WebsiteDao与WebsiteService一样

       public interface WebsiteDao {
     boolean remove(Integer id);
     boolean remove(List<Integer> ids);
     boolean save(Website education);
     Website get(Integer id);
     List<Website> list();
     int count();
 }

  6. Impl类都添加接口实现

     public class EducationDaoImpl implements EducationDao {}
 public class WebsiteDaoImpl implements WebsiteDao {}
 public class EducationServiceImpl implements EducationService {}
 public class WebsiteServiceImpl implements WebsiteService {}

  7. 目前的对象拥有连接是：Servlet拥有Service对象，Service对象拥有Dao对象，现在分别将Servlet与ServiceImpl对象中的拥有修改成接口引用

     Servlet拥有Service接口
 private EducationService service = new EducationServiceImpl();
 private WebsiteService service = new WebsiteServiceImpl();
    
 ServiceImpl对象拥有Dao接口
 private EducationDao dao = new EducationDaoImpl();
 private WebsiteDao dao = new WebsiteDaoImpl();

dao层抽取

  1. 接口抽取

    1. 在dao下新建一个BaseDao，抽取代码如下

       package com.zh.xr.dao;
 import java.util.List;
        
 public interface BaseDao<T> {
     boolean remove(Integer id);
     boolean remove(List<Integer> ids);
     boolean save(T bean);
     T get(Integer id);
     List<T> list();
     int count();
 }

    2. EducationDao跟WebsiteDao如下：

       public interface EducationDao extends BaseDao<Education>{}
 public interface WebsiteDao extends BaseDao<Website> {}
  2. Impl抽取

    1. 在dao文件夹下新建一个BaseDaoImpl,将Impl中的count、remove方法抽取出来

       public abstract class BaseDaoImpl<T> implements BaseDao<T> {
     private String table = table();
     //要求子类实现，告知表名
     protected abstract String table();
        
     public boolean remove(Integer id) {
         String sql = "DELETE FROM" + table + " WHERE id = ? ";
         return Dbs.getTpl().update(sql,id) >0 ;
     }
        
     public boolean remove(List<Integer> ids) {
         List<Object> args = new ArrayList<>();
         StringBuilder sql = new StringBuilder();
         sql.append("DELETE FROM ").append(table).append(" WHERE id in (");
         for (Integer id: ids) {
             args.add(id);
             sql.append("?, ");
         }
         sql.replace(sql.length()-2,sql.length(),")");
        
         return Dbs.getTpl().update(sql.toString(),args.toArray()) >0 ;
     }
     public int count() {
         String sql = "SELECT COUNT(*) FROM " + table;
         return Dbs.getTpl().queryForObject(sql, new BeanPropertyRowMapper<>(Integer.class));
     }
 }

    2. EducationDaoImpl

       public class EducationDaoImpl extends BaseDaoImpl<Education> implements EducationDao {

     @Override
     protected String table() {
         return "education";
     }
     public boolean save(Education education) {
         Integer id = education.getId();
         List<Object> args = new ArrayList<>();
         args.add(education.getName());
         args.add(education.getType());
         args.add(education.getIntro());
         args.add(education.getBeginDay());
         args.add(education.getEndDay());
         String sql = "";
         if(id == null || id <1){
             sql = "INSERT INTO education(name,type,intro,begin_day,end_day) VALUES(?, ?, ?, ?, ?)";
         }else {
             sql = "UPDATE education SET name = ?, type = ?, intro = ?, begin_day = ?, end_day = ? WHERE id = ?";
             args.add(id);
         }
         return Dbs.getTpl().update(sql,args.toArray()) >0 ;
     }
        
     public Education get(Integer id) {
         String sql = "SELECT id, created_time, name, type, intro, begin_day, end_day FROM education WHERE id = ?";
         return Dbs.getTpl().queryForObject(sql,new BeanPropertyRowMapper<>(Education.class),id);
     }
     public List<Education> list() {
         String sql = "SELECT id, created_time, name, type, intro, begin_day, end_day FROM education";
         return Dbs.getTpl().query(sql,new BeanPropertyRowMapper<>(Education.class));
     }
 }

    3. WebsiteDaoImpl

       public class WebsiteDaoImpl extends BaseDaoImpl<Website> implements WebsiteDao {
     @Override
     protected String table() {
         return "website";
     }
     public boolean save(Website website) {
         Integer id = website.getId();
         List<Object> args = new ArrayList<>();
         args.add(website.getFooter());
         String sql = "";
         if(id == null || id <1){
             sql = "INSERT INTO website(footer) VALUES(?)";
         }else {
             sql = "UPDATE website SET footer = ? WHERE id = ?";
             args.add(id);
         }
         return Dbs.getTpl().update(sql,args.toArray()) >0 ;
     }
     public Website get(Integer id) {
         return null;
     }
     
     public List<Website> list() {
         String sql = "SELECT id, created_time, footer FROM website";
         return Dbs.getTpl().query(sql,new BeanPropertyRowMapper<>(Website.class));
     }
 }

service抽取

  1. 接口抽取

    1. 同理抽取service，新建一个BaseService，然后抽取

       public interface BaseService<T>{
     boolean remove(Integer id);
     boolean remove(List<Integer> ids);
     boolean save(T bean);
     T get(Integer id);
     List<T> list();
     int count();
 }

    2. EducationService/WebsiteService

       public interface WebsiteService extends BaseService<Website> {}
 public interface EducationService extends BaseService<Education>{}
  2. Impl抽取

    1. 新建BaseServiceImpl

       public abstract class BaseServiceImpl<T> implements BaseService<T> {
     private BaseDao<T> dao = dao();
     protected abstract  BaseDao<T> dao();
     public boolean remove(Integer id) {
         return dao.remove(id);
     }
     public boolean remove(List<Integer> ids) {
         return dao.remove(ids);
     }
     public boolean save(T bean) {
         return dao.save(bean) ;
     }
     public T get(Integer id) {
         return dao.get(id);
     }
     public List<T> list() {
         return dao.list();
     }
     public int count() {
         return dao.count();
     }
 }

    2. EducationServiceImpl、WebsiteServiceImpl

       public class WebsiteServiceImpl extends BaseServiceImpl<Website> implements WebsiteService {
     @Override
     protected BaseDao<Website> dao() {
         return new WebsiteDaoImpl();
     }
 }
 public class EducationServiceImpl extends BaseServiceImpl<Education> implements EducationService {
     @Override
     protected BaseDao<Education> dao() {
         return new EducationDaoImpl();
     }
 }

专业技能

  1. 参照教育经验，依次新建bean（skill）->Dao（SkillDao、SkillDaoImpl）->Service(SkillService/SkillServiceImpl)->Servlet(SkillServlet)->skill.jsp即可完成

自定义错误页面

404页面定义

  1. 当用户访问了一个不存在的页面（IP+端口对的，但是页面不存在），会报404，通常这个页面不够友好，如何自定义呢？

  2. 在项目的WEB-INF下的web.xml下配置

     <!-- 配置404页面 -->
 <error-page>
     <error-code>404</error-code>
     <location>/WEB-INF/page/404.jsp</location>
 </error-page>

 <!-- 配置500页面 -->
 <error-page>
     <error-code>500</error-code>
     <location>/WEB-INF/page/500.jsp</location>
 </error-page>
  3. 一旦访问结果为404，就跳转到404.jsp，比如：http://localhost:8080/xr/skill.jsp

500页面定义

  1. 什么情况服务器会抛出500呢？ 当代码的异常直接抛给Tomcat时，就会报500异常

     //将BaseServlet中的doget方法中的异常直接抛向外抛出
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     try {
        ...
     } catch (Exception e) {
         e.printStackTrace();
         //异常直接向外抛出
         throw new ServletException("方法找不到");
     }
 }
    1. 浏览器访问：http://localhost:8080/xr/skill/adminxxxx就会转发到500.jsp页面

错误路径访问页面定义

  1. 上面讲过500是程序代码出现异常直接抛出给了Tomcat才出现500，但是如果异常没有抛出去呢？我们直接拦截了呢？此时如输错误路径，整个页面会显示空白

  2. 解决办法通过内部转发到自定义的错误页面

     //将BaseServlet中的doget方法中的异常不向外抛出
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     try {
        ...
     } catch (Exception e) {
         e.printStackTrace();
         //异常不向外抛出，转发
         //目的是找到最终引起故障的原因
         Throwable cause = e;
         while (cause.getCause() != null){
             cause = cause.getCause();
         }
         request.setAttribute("error",cause.getClass().getName());
         request.getRequestDispatcher("/WEB-INF/page/error.jsp").forward(request,response);
     }
 }

图片上传功能

  1. 图片如何存储到服务器？
    1. 服务器将客户端发过来的图片数据直接写入到服务器的硬盘中，然后将图片路径地址存储到数据库中，并不是将图片数据直接存储到数据库中

获奖成就模块

  1. 参照教育经验，依次新建bean（Award）->Dao（AwardDao、AwardDaoImpl）->Service(AwardService/AwardServiceImpl)->Servlet(AwardServlet)->award.jsp即可完成

form文件上传-前端

  1. 如果要支持文件上传，必须设置2个属性

     method="post"
 enctype="multipart/form-data"

  2. 一旦form设置了这一项，Java后台就无法通过request.getParameter获取参数

文件上传-后台

  1. Java后台中常使用commons-fileupload来接收客户端上传的文件

  2. pom.xml中添加

     <dependency>
     <groupId>commons-fileupload</groupId>
     <artifactId>commons-fileupload</artifactId>
     <version>1.4</version>
 </dependency>

  3. AwardServlet中的save方法如下：

     public void save(HttpServletRequest request, HttpServletResponse response) throws Exception {
     DiskFileItemFactory factory = new DiskFileItemFactory();
     ServletFileUpload upload = new ServletFileUpload(factory);
     //解决中文文件名乱码问题
     upload.setHeaderEncoding("UTF-8");
     //一个FileItem代表一个请求参数，包括文件参数、非文件参数。
     List<FileItem> items = upload.parseRequest(request);
     //存储非文件参数
     Map<String,Object> params = new HashMap<>();
     //存储到数据库的文件路径
     String imagurl = null;
     for (FileItem item : items) {
         //参数名称
         String fieldName = item.getFieldName();
         //参数值
         String value = item.getString();
         if (item.isFormField()){//非文件参数
             System.out.println(fieldName + "_" + item.getString("UTF-8"));
             params.put(item.getFieldName(),item.getString("UTF-8"));
         }else {//是文件参数
             System.out.println(fieldName + "_" + item.getName());
             //文件名称
             //System.out.println(item.getName());
             //参数名称
             //System.out.println(item.getFieldName());
             //具体数据
             //System.out.println(item.getString());
             //将文件数据写到硬盘中
             //1. 拿到当前项目在磁盘上的绝对路径（打包后的项目路径）+自定义文件存放路径
             String dir = request.getServletContext().getRealPath("upload/img");
             //2. 设置文件名（不能直接使用客户端直接传递过来的文件名，防止冲突覆盖）
             //随机码+扩展名
             String fileName = UUID.randomUUID() + "." + FilenameUtils.getExtension(item.getName());
             //3.最终文件路径
             imagurl = "upload/img" +"/" + fileName;
             String filepath = dir +"/" + fileName;
             System.out.println(filepath);
             //4. 将文件写入到路径中
             //使用原生解析
             //FileOutputStream outputStream = new FileOutputStream(new File(filepath));
             //读取客户端发送过来的文件数据
             //InputStream Ins = item.getInputStream();
             //byte[] buffer = new byte[4096];
             //int len;
             //while ((len = Ins.read(buffer)) != -1){
             //    outputStream.write(buffer,0,len);
             //}
             //Ins.close();
             //outputStream.close();
             //使用第三方框架接收
             FileUtils.copyInputStreamToFile(item.getInputStream(),new File(filepath));
         }
     }
     //5. 将文件路径写入到数据库中
     //注意：客户端访问图片时，域名+固定路径，而不是上面的filepath，因此存入到数据库的仅仅是上面的`upload/img/xxxxx.png`
     //imageUrl
     Award award = new Award();
     //正常参数
     BeanUtils.populate(award, params);
     //图片路径参数
     //因为编辑的时候，如果没有重新上传图片，那就不需要再次走文件上传了
     if(award.getImage() == null){
         award.setImage(imagurl);
     }
     if (service.save(award)) {//保存成功
         //重定向到admin
         response.sendRedirect(request.getContextPath() + "/award/admin");
     }else {//保存失败
         request.setAttribute("error","获奖成就保存失败");
         request.getRequestDispatcher("/WEB-INF/page/error.jsp").forward(request,response);
     }
 }

  4. save精简后的代码

     public void save(HttpServletRequest request, HttpServletResponse response) throws Exception {
     DiskFileItemFactory factory = new DiskFileItemFactory();
     ServletFileUpload upload = new ServletFileUpload(factory);
     //解决中文文件名乱码问题
     upload.setHeaderEncoding("UTF-8");
     //一个FileItem代表一个请求参数，包括文件参数、非文件参数。
     List<FileItem> items = upload.parseRequest(request);
     //存储非文件参数
     Map<String,Object> params = new HashMap<>();
     //存储文件数据
     Map<String,FileItem> fileParams = new HashMap<>();
     //存储到数据库的文件路径
     for (FileItem item : items) {
         //参数名称
         String fieldName = item.getFieldName();
         if (item.isFormField()){//非文件参数
             params.put(fieldName,item.getString("UTF-8"));
         }else {//是文件参数
             fileParams.put(fieldName,item);
         }
     }
     Award award = new Award();
     BeanUtils.populate(award, params);
     if (award.getImage() != null && award.getImage().length() == 0){
         award.setImage(null);
     }
     FileItem item = fileParams.get("imageFile");
     if(item != null){
         InputStream is = item.getInputStream();
         if (is.available() >0 ){
             //将文件数据写到硬盘中
             String fileName = UUID.randomUUID() + "." + FilenameUtils.getExtension(item.getName());
             //3.最终文件路
             String image  = "upload/img" +"/" + fileName;
             String filepath = request.getServletContext().getRealPath(image);
             System.out.println(filepath);
             //4. 将文件写入到路径中
             //使用第三方框架接收
             FileUtils.copyInputStreamToFile(item.getInputStream(),new File(filepath));
             award.setImage(image);
         }
     }
     if (service.save(award)) {//保存成功
         //重定向到admin
         response.sendRedirect(request.getContextPath() + "/award/admin");
     }else {//保存失败
         request.setAttribute("error","获奖成就保存失败");
         request.getRequestDispatcher("/WEB-INF/page/error.jsp").forward(request,response);
     }
 }

文件上传功能封装

  1. 很多模块都会用到上传功能，那么就需要将其封装起来
  2. 在util文件夹下新建一个工具类Uploads

  3. 代码举例：

     public class Uploads {
     private static final String BASE_DIR = "upload";
     private static final String IMG_DIR = "img";
    
     /**
      * 图片上传
      * @param item 文件参数
      * @param request 请求
      * @param oldImage 以前的图片路径
      * @return 存储到数据库的图片路径
      * @throws Exception
      */
     public static String uploadImage(FileItem item, HttpServletRequest request, String oldImage) throws Exception {
         // 如果oldImage是空字符串，就设置为null
         if (oldImage != null && oldImage.length() == 0) {
             oldImage = null;
         }
    
         if (item == null) return oldImage;
         InputStream is = item.getInputStream();
         if (is.available() == 0) return oldImage;
    
         ServletContext ctx = request.getServletContext();
    
         String filename = UUID.randomUUID() + "." + FilenameUtils.getExtension(item.getName());
         String image = BASE_DIR + "/" + IMG_DIR + "/" + filename;
         String filepath = ctx.getRealPath(image);
         FileUtils.copyInputStreamToFile(item.getInputStream(), new File(filepath));
    
         // 删除旧的文件,防止旧图片累积
         if (oldImage != null) {
             // 如果oldImage是空串，那么就会把整个web项目的文件夹给删掉
             FileUtils.deleteQuietly(new File(ctx.getRealPath(oldImage)));
         }
    
         return image;
     }
 }

  4. AwardServlet中save代码

     public void save(HttpServletRequest request, HttpServletResponse response) throws Exception {
     DiskFileItemFactory factory = new DiskFileItemFactory();
     ServletFileUpload upload = new ServletFileUpload(factory);
     //解决中文文件名乱码问题
     upload.setHeaderEncoding("UTF-8");
     //一个FileItem代表一个请求参数，包括文件参数、非文件参数。
     List<FileItem> items = upload.parseRequest(request);
     //存储非文件参数
     Map<String,Object> params = new HashMap<>();
     //存储文件数据
     Map<String,FileItem> fileParams = new HashMap<>();
     //存储到数据库的文件路径
     for (FileItem item : items) {
         //参数名称
         String fieldName = item.getFieldName();
         if (item.isFormField()){//非文件参数
             params.put(fieldName,item.getString("UTF-8"));
         }else {//是文件参数
             fileParams.put(fieldName,item);
         }
     }
     //5. 将文件路径写入到数据库中
     //注意：客户端访问图片时，域名+固定路径，而不是上面的filepath，因此存入到数据库的仅仅是上面的`upload/img/xxxxx.png`
     //imageUrl
     Award award = new Award();
     BeanUtils.populate(award, params);
     FileItem item = fileParams.get("imageFile");
     award.setImage(Uploads.uploadImage(item,request,award.getImage()));
     if (service.save(award)) {//保存成功
         //重定向到admin
         response.sendRedirect(request.getContextPath() + "/award/admin");
     }else {//保存失败
         request.setAttribute("error","获奖成就保存失败");
         request.getRequestDispatcher("/WEB-INF/page/error.jsp").forward(request,response);
     }
 }

问题分析

  1. 刚上传完毕的图片，有可能会出现无法实时预览的问题（要等一会再次刷新才能预览成功）

  2. 把Tomcat的缓存资源功能关掉即可，在%TOMCAT_HOME%/conf/context.xml中增加Resources标签

     //在Context标签中添加
 <Resources
   cachingAllowed="false"
   cacheMaxSize="0"
 />

Servlet抽取

  1. 将各个servlet中的转发与重定向重复代码抽取到BaseServlet中

  2. 封装3个函数,共其他servlet调用

     redirect
 forward
 forwardError

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