项目实战：service业务逻辑组件引入

1、第一层DAO层

1.1、FruitDao接口

package com.csdn.fruit.dao;
import com.csdn.fruit.pojo.Fruit;
import java.util.List;
//dao ：Data Access Object 数据访问对象
//接口设计
public interface FruitDao {void addFruit(Fruit fruit);void delFruit(String fname);//通过 fid 删除 水果库存记录void delFruitByFid(Integer fid);void updateFruit(Fruit fruit);@DeprecatedList<Fruit> getFruitList();@DeprecatedList<Fruit> getFruitList(Integer pageNo, Integer pageSize);List<Fruit> getFruitList(Integer pageNo, Integer pageSize,String keyword);Fruit getFruitByFname(String fname);Fruit getFruitByFid(Integer fid);//查询总记录条数@DeprecatedInteger getRecordCount();Integer getRecordCount(String keyword);
}

1.2、FruitDaoImpl实现类

package com.csdn.fruit.dao.impl;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.mymvc.dao.BaseDao;
import java.util.List;
public class FruitDaoImpl extends BaseDao<Fruit> implements FruitDao {@Overridepublic void addFruit(Fruit fruit) {String sql = "insert into t_fruit values (0,?,?,?,?)";super.executeUpdate(sql, fruit.getFname(), fruit.getPrice(), fruit.getFcount(), fruit.getRemark());}@Overridepublic void delFruit(String fname) {String sql = "delete from t_fruit where fname=?";super.executeUpdate(sql, fname);}//通过 fid 删除水果库存记录@Overridepublic void delFruitByFid(Integer fid) {super.executeUpdate("delete from t_fruit where fid = ? ", fid);}//通过 fid 可以修改所有的属性值@Overridepublic void updateFruit(Fruit fruit) {String sql = "update  t_fruit set fname=?,price=?,fcount=?,remark=? where fid = ?";super.executeUpdate(sql, fruit.getFname(), fruit.getPrice(), fruit.getFcount(), fruit.getRemark(), fruit.getFid());}@Overridepublic List<Fruit> getFruitList() {return super.executeQuery("select * from t_fruit");}@Overridepublic List<Fruit> getFruitList(Integer pageNo, Integer pageSize) {return super.executeQuery("select * from t_fruit limit ?,?", (pageNo - 1) * pageSize, pageSize);}@Overridepublic List<Fruit> getFruitList(Integer pageNo, Integer pageSize, String keyword) {return super.executeQuery("select * from t_fruit where fname like ? or remark like?  limit ?,?", "%" + keyword + "%", "%" + keyword + "%", (pageNo - 1) * pageSize, pageSize);}@Overridepublic Fruit getFruitByFname(String fname) {return load("select * from t_fruit where fname = ?", fname);}@Overridepublic Fruit getFruitByFid(Integer fid) {return load("select * from t_fruit where fid=?", fid);}@Overridepublic Integer getRecordCount() {String sql = "select count(*) from t_fruit";return ((Long) executeComplexQuery(sql).get(0)[0]).intValue();}@Overridepublic Integer getRecordCount(String keyword) {String sql = "select count(*) from t_fruit where fname like ? or remark like ? ";return ((Long) executeComplexQuery(sql, "%" + keyword + "%", "%" + keyword + "%").get(0)[0]).intValue();}
}

2、第二层Service层

2.1、FruitService接口

package com.csdn.fruit.service;
import com.csdn.fruit.dto.PageInfo;
import com.csdn.fruit.dto.PageQueryParam;
import com.csdn.fruit.pojo.Fruit;
public interface FruitService {PageInfo<Fruit> getFruitPageInfo(PageQueryParam pageQueryParam);void addFruit(Fruit fruit);void updateFruit(Fruit fruit);void delFruit(Integer fid);Fruit getFruitById(Integer fid);Fruit getFruitByFname(String fname);
}

2.2、FruitServiceImpl实现类

package com.csdn.fruit.service.impl;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
import com.csdn.fruit.dto.PageInfo;
import com.csdn.fruit.dto.PageQueryParam;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.service.FruitService;
import java.util.List;
public class FruitServiceImpl implements FruitService {private FruitDao fruitDao = new FruitDaoImpl();@Overridepublic PageInfo<Fruit> getFruitPageInfo(PageQueryParam pageQueryParam) {Integer pageNo = pageQueryParam.getPageNo();Integer pageSize = pageQueryParam.getPageSize();String keyword = pageQueryParam.getKeyword();List<Fruit> fruitList = fruitDao.getFruitList(pageNo, pageSize, keyword);Integer recordCount = fruitDao.getRecordCount(pageQueryParam.getKeyword());PageInfo<Fruit> fruitPageInfo = new PageInfo<>(fruitList, pageNo, recordCount);return fruitPageInfo;}@Overridepublic void addFruit(Fruit fruit) {if (fruitDao.getFruitByFname(fruit.getFname()) == null) {fruitDao.addFruit(fruit);}}@Overridepublic void updateFruit(Fruit fruit) {fruitDao.updateFruit(fruit);}@Overridepublic void delFruit(Integer fid) {fruitDao.delFruitByFid(fid);}@Overridepublic Fruit getFruitById(Integer fid) {return fruitDao.getFruitByFid(fid);}@Overridepublic Fruit getFruitByFname(String fname) {return fruitDao.getFruitByFname(fname);}
}

3、Servlet层

3.1、IndexServlet

package com.csdn.fruit.servlet;
import com.csdn.fruit.dto.PageInfo;
import com.csdn.fruit.dto.PageQueryParam;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.service.FruitService;
import com.csdn.fruit.service.impl.FruitServiceImpl;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/index")
public class IndexServlet extends HttpServlet {private FruitService fruitService = new FruitServiceImpl();@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Integer pageNo = 1;String pageNoStr = req.getParameter("pageNo");if (pageNoStr != null && !"".equals(pageNoStr)) {pageNo = Integer.parseInt(pageNoStr);}String keyword = "";String keywordStr = req.getParameter("keyword");if (keywordStr!=null) {keyword = keywordStr;}PageQueryParam pageQueryParam = new PageQueryParam(pageNo, 5, keyword);PageInfo<Fruit> pageInfo = fruitService.getFruitPageInfo(pageQueryParam);Result result = Result.OK(pageInfo);ResponseUtil.print(resp, result);}
}

3.2、EditServlet

package com.csdn.fruit.servlet;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.service.FruitService;
import com.csdn.fruit.service.impl.FruitServiceImpl;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/edit")
public class EditServlet extends HttpServlet {private FruitService fruitService = new FruitServiceImpl();@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Integer fid = Integer.parseInt(req.getParameter("fid"));Fruit fruit = fruitService.getFruitById(fid);ResponseUtil.print(resp, Result.OK(fruit));}
}

3.3、GetFnameServlet

package com.csdn.fruit.servlet;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.service.FruitService;
import com.csdn.fruit.service.impl.FruitServiceImpl;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.GenericServlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.annotation.WebServlet;
import java.io.IOException;
@WebServlet("/getFname")
public class GetFnameServlet extends GenericServlet {private FruitService fruitService = new FruitServiceImpl();@Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {String fname = servletRequest.getParameter("fname");Fruit fruit = fruitService.getFruitByFname(fname);ResponseUtil.print(servletResponse, fruit == null ? Result.OK() : Result.Fail());}
}

3.4、UpdateServlet

package com.csdn.fruit.servlet;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.service.FruitService;
import com.csdn.fruit.service.impl.FruitServiceImpl;
import com.csdn.fruit.util.RequestUtil;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/update")
public class UpdateServlet extends HttpServlet {private FruitService fruitService = new FruitServiceImpl();@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Fruit fruit = (Fruit) RequestUtil.readObject(req, Fruit.class);fruitService.updateFruit(fruit);ResponseUtil.print(resp, Result.OK());}
}

3.5、DelServlet

package com.csdn.fruit.servlet;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.service.FruitService;
import com.csdn.fruit.service.impl.FruitServiceImpl;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/del")
public class DelServlet extends HttpServlet {private FruitService fruitService = new FruitServiceImpl();@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Integer fid = Integer.parseInt(req.getParameter("fid"));fruitService.delFruit(fid);ResponseUtil.print(resp, Result.OK());}
}

3.6、AddServlet

package com.csdn.fruit.servlet;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.service.FruitService;
import com.csdn.fruit.service.impl.FruitServiceImpl;
import com.csdn.fruit.util.RequestUtil;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/add")
public class AddServlet extends HttpServlet {private FruitService fruitService = new FruitServiceImpl();@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Fruit fruit = (Fruit) RequestUtil.readObject(req, Fruit.class);fruitService.addFruit(fruit);ResponseUtil.print(resp, Result.OK());}
}

4、DTO层

4.1、Result

package com.csdn.fruit.dto;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Result {private boolean flag;private Object data;private String msg;public Result(boolean flag, Object data) {this.flag = flag;this.data = data;}public Result(boolean flag, String msg) {this.flag = flag;this.msg = msg;}public static Result OK() {return new Result(true, "操作成功");}public static Result OK(Object data) {return new Result(true, data);}public static Result Fail() {return new Result(false, "操作失败");}public static Result Fail(String msg) {return new Result(false, msg);}
}

4.2、PageInfo

package com.csdn.fruit.dto;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.util.List;
//分页组件类
@Data
@NoArgsConstructor
@AllArgsConstructor
public class PageInfo<T> {private List<T> list;private Integer pageNo = 1;private Integer pageSize = 5;private Integer recordCount = 0;private Integer pageCount = 0;public PageInfo(List<T> list, Integer pageNo, Integer recordCount) {this.list = list;this.pageNo = pageNo;this.recordCount = recordCount;this.pageCount = (recordCount + pageSize - 1) / pageSize;}
}

4.3、PageQueryParam

package com.csdn.fruit.dto;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
@AllArgsConstructor
public class PageQueryParam {private Integer pageNo = 1;private Integer pageSize = 5;private String keyword = "";
}

5、Util层

5.1、RequestUtil

package com.csdn.fruit.util;
import jakarta.servlet.ServletRequest;
import java.io.BufferedReader;
import java.io.IOException;
public class RequestUtil {public static Object readObject(ServletRequest request, Class clazz) throws IOException {BufferedReader br = request.getReader();StringBuilder stringBuilder = new StringBuilder();String str = null;while ((str = br.readLine()) != null) {stringBuilder.append(str);}str = stringBuilder.toString();return GsonUtil.fromJson(str, clazz);}
}

5.2、GsonUtil

package com.csdn.fruit.util;
import com.google.gson.Gson;
public class GsonUtil {public static String toJson(Object obj) {//java object ->  json stringGson gson = new Gson();return gson.toJson(obj);}//public static <T> T fromJson(String jsonStr, Class<T> clazz) {}public static Object fromJson(String jsonStr, Class clazz) {// json string -> java objectGson gson = new Gson();return gson.fromJson(jsonStr, clazz);}
}

5.3、ResponseUtil

package com.csdn.fruit.util;
import com.csdn.fruit.dto.Result;
import jakarta.servlet.ServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class ResponseUtil {public static void print(ServletResponse response, Result result) throws IOException {response.setCharacterEncoding("UTF-8");response.setContentType("application/json;charset=utf-8");PrintWriter out = response.getWriter();out.println(GsonUtil.toJson(result));out.flush();}
}

6、Service层的文字解读

Java中的service层一般是作为业务逻辑处理的中间层，负责接收控制层的请求，进行业务逻辑的处理，并将处理结果返回给控制层。

具体来说，service层通常包括以下作用：

转发控制层请求：service层一般是与控制层紧密联系的，负责接收控制层的请求，通过调用DAO层提供的接口获取数据，进行业务逻辑的处理，并将处理结果返回给控制层。

处理业务逻辑：service层主要负责对业务逻辑进行处理，将底层的数据操作进行组合和加工，从而形成业务流程，实现对复杂业务操作的封装，方便控制层调用。

事务处理：service层通常是一个事务的边界，负责管理一系列操作的一致性和完整性，确保业务操作的正确性。

异常处理：service层也负责处理操作过程中的异常，确保业务操作的可靠性和稳定性，通过对异常的处理，提高系统的容错能力。

综上，service层在Java应用程序中扮演着重要的角色，起到了整合、控制和管理业务逻辑的作用，是一个高层次的、中间的业务处理层。