# JaveWeb的文件執行方式
###### tags: `Java Web`

## 1.執行流程
### 1.客戶端傳送add.html指令到服務器端
### 2.服務器端調出add.html的資料，回傳到服務器端
### 3.add.html的指令"action = "add" "，會觸發服務器端的add指令
### 4.add指令調用AddServlet的方法
#### (1)獲取客戶端發送的數據
#### (2)調用DAO中的方法完成添加功能
#### (3)在控制台打印成功

## 2.AddServlet文件撰寫
### (1)需要繼承HttpServlet類別：
在Servlet的導包中取得，因此需要導入Tomcat的導包
#### 導包的方式

package com.atguigu.servlets;

import com.atguigu.servlets.dao.FruitDAO;
import com.atguigu.servlets.dao.impl.FruitDAOImpl;
import com.atguigu.servlets.pojo.Fruit;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class AddServlet extends HttpServlet {
    //doPost：響應html文件中的method="post"請求
    //request：客戶端發送的數據會包裝成request
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //getParameter：獲取數據中的參數，只能是String(若是其他類，要自行強轉)
        String fname = request.getParameter("fname");
        String priceStr = request.getParameter("price");
        Integer price = Integer.parseInt(priceStr);
        String fcountStr = request.getParameter("fcount");
        Integer fcount = Integer.parseInt(fcountStr);
        String remark = request.getParameter("remark");

       System.out.println("fname = " +fname);
       System.out.println("price = " +price);
       System.out.println("fcount = " +fcount);
       System.out.println("remark = " +remark);

    }
}

## 3.設置action="add"與AddServlet的對應關係
指令action="add"並不會直接調用AddServlet.java的指令，而是要透過編輯WEB-INF底下的web.xml才能確立兩者的對應關係。

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>AddServlet</servlet-name>
        <servlet-class>com.atguigu.servlets.AddServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>AddServlet</servlet-name>
        <url-pattern>/add</url-pattern>
    </servlet-mapping>
    <!--
    1.用戶發請求，action = add
    2.項目中，web.xml中找到url-pattern = /add ->第12行
    3.找第11行的 servlet-name = AddServlet
    4.找和servlet-mapping中servlet-name一致的servlet，找到第7行
    5.找第8行的servlet-class ->com.atguigu.servlets.AddServlet
    6.用戶發送的是post請求(method = post)，因此tomcat會執行AddServlet中的doPost方法
    -->
</web-app>

### 4.運行
#### 在網頁中生成請求
#### 請求過程
1.向pro07/add發送請求，請求方式"post"
2.控制台看到的打印值
3.建立對應的Fruit、FruitDAOImpl、BaseDAO文件
#### 实体类

package com.atguigu.servlets.pojo;

public class Fruit {
    private Integer fid ;
    private String fname ;
    private Integer price ;
    private Integer fcount ;
    private String remark ;

    public Fruit(){}

    public Fruit(Integer fid, String fname, Integer price, Integer fcount, String remark) {
        this.fid = fid;
        this.fname = fname;
        this.price = price;
        this.fcount = fcount;
        this.remark = remark;
    }

    public Integer getFid() {
        return fid;
    }

    public void setFid(Integer fid) {
        this.fid = fid;
    }

    public String getFname() {
        return fname;
    }

    public void setFname(String fname) {
        this.fname = fname;
    }

    public Integer getPrice() {
        return price;
    }

    public void setPrice(Integer price) {
        this.price = price;
    }

    public Integer getFcount() {
        return fcount;
    }

    public void setFcount(Integer fcount) {
        this.fcount = fcount;
    }

    public String getRemark() {
        return remark;
    }

    public void setRemark(String remark) {
        this.remark = remark;
    }

    @Override
    public String toString() {
        return fid + "\t\t" + fname + "\t\t" + price +"\t\t" + fcount +"\t\t" + remark ;
    }
}

#### DAO 实现类

package com.atguigu.servlets.dao.impl;


import com.atguigu.servlets.dao.FruitDAO;
import com.atguigu.servlets.dao.base.BaseDAO;
import com.atguigu.servlets.pojo.Fruit;

import java.util.List;

public class FruitDAOImpl extends BaseDAO<Fruit> implements FruitDAO {
    @Override
    public List<Fruit> getFruitList() {
        return super.executeQuery("select * from t_fruit");
    }

    @Override
    public boolean addFruit(Fruit fruit) {
        String sql = "insert into t_fruit values(0,?,?,?,?)";
        int count = super.executeUpdate(sql,fruit.getFname(),fruit.getPrice(),fruit.getFcount(),fruit.getRemark()) ;
        //insert语句返回的是自增列的值，而不是影响行数
        //System.out.println(count);
        return count>0;
    }

    @Override
    public boolean updateFruit(Fruit fruit) {
        String sql = "update t_fruit set fcount = ? where fid = ? " ;
        return super.executeUpdate(sql,fruit.getFcount(),fruit.getFid())>0;
    }

    @Override
    public Fruit getFruitByFname(String fname) {
        return super.load("select * from t_fruit where fname like ? ",fname);
    }

    @Override
    public boolean delFruit(String fname) {
        String sql = "delete from t_fruit where fname like ? " ;
        return super.executeUpdate(sql,fname)>0;
    }
}

#### 连接数据库

package com.atguigu.servlets.dao.base;

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public abstract class BaseDAO<T> {
    public final String DRIVER = "com.mysql.jdbc.Driver" ;
    public final String URL = "jdbc:mysql://localhost:3306/fruitdb?useUnicode=true&characterEncoding=utf-8&useSSL=false";
    public final String USER = "root";
    public final String PWD = "123456" ;

    protected Connection conn ;
    protected PreparedStatement psmt ;
    protected ResultSet rs ;

    //T的Class对象
    private Class entityClass ;

    public BaseDAO(){
        //getClass() 获取Class对象，当前我们执行的是new FruitDAOImpl() , 创建的是FruitDAOImpl的实例
        //那么子类构造方法内部首先会调用父类（BaseDAO）的无参构造方法
        //因此此处的getClass()会被执行，但是getClass获取的是FruitDAOImpl的Class
        //所以getGenericSuperclass()获取到的是BaseDAO的Class
        Type genericType = getClass().getGenericSuperclass();
        //ParameterizedType 参数化类型
        Type[] actualTypeArguments = ((ParameterizedType) genericType).getActualTypeArguments();
        //获取到的<T>中的T的真实的类型
        Type actualType = actualTypeArguments[0];
        try {
            entityClass = Class.forName(actualType.getTypeName());
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    protected Connection getConn(){
        try {
            //1.加载驱动
            Class.forName(DRIVER);
            //2.通过驱动管理器获取连接对象
            return DriverManager.getConnection(URL, USER, PWD);
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }
        return null ;
    }

    protected void close(ResultSet rs , PreparedStatement psmt , Connection conn){
        try {
            if (rs != null) {
                rs.close();
            }
            if(psmt!=null){
                psmt.close();
            }
            if(conn!=null && !conn.isClosed()){
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    //给预处理命令对象设置参数
    private void setParams(PreparedStatement psmt , Object... params) throws SQLException {
        if(params!=null && params.length>0){
            for (int i = 0; i < params.length; i++) {
                psmt.setObject(i+1,params[i]);
            }
        }
    }

    //执行更新，返回影响行数
    protected int executeUpdate(String sql , Object... params){
        boolean insertFlag = false ;
        insertFlag = sql.trim().toUpperCase().startsWith("INSERT");
        try {
            conn = getConn();
            if(insertFlag){
                psmt = conn.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);
            }else {
                psmt = conn.prepareStatement(sql);
            }
            setParams(psmt,params);
            int count = psmt.executeUpdate() ;

            rs = psmt.getGeneratedKeys();
            if(rs.next()){
                return ((Long)rs.getLong(1)).intValue();
            }
            return count ;
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            close(rs,psmt,conn);
        }
        return 0;
    }

    //通过反射技术给obj对象的property属性赋propertyValue值
    private void setValue(Object obj ,  String property , Object propertyValue){
        Class clazz = obj.getClass();
        try {
            //获取property这个字符串对应的属性名 ， 比如 "fid"  去找 obj对象中的 fid 属性
            Field field = clazz.getDeclaredField(property);
            if(field!=null){
                field.setAccessible(true);
                field.set(obj,propertyValue);
            }
        } catch (NoSuchFieldException | IllegalAccessException e) {
            e.printStackTrace();
        }
    }

    //执行复杂查询，返回例如统计结果
    protected Object[] executeComplexQuery(String sql , Object... params){
        try {
            conn = getConn() ;
            psmt = conn.prepareStatement(sql);
            setParams(psmt,params);
            rs = psmt.executeQuery();

            //通过rs可以获取结果集的元数据
            //元数据：描述结果集数据的数据 , 简单讲，就是这个结果集有哪些列，什么类型等等

            ResultSetMetaData rsmd = rs.getMetaData();
            //获取结果集的列数
            int columnCount = rsmd.getColumnCount();
            Object[] columnValueArr = new Object[columnCount];
            //6.解析rs
            if(rs.next()){
                for(int i = 0 ; i<columnCount;i++){
                    Object columnValue = rs.getObject(i+1);     //33    苹果      5
                    columnValueArr[i]=columnValue;
                }
                return columnValueArr ;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            close(rs,psmt,conn);
        }
        return null ;
    }

    //执行查询，返回单个实体对象
    protected T load(String sql , Object... params){
        try {
            conn = getConn() ;
            psmt = conn.prepareStatement(sql);
            setParams(psmt,params);
            rs = psmt.executeQuery();

            //通过rs可以获取结果集的元数据
            //元数据：描述结果集数据的数据 , 简单讲，就是这个结果集有哪些列，什么类型等等

            ResultSetMetaData rsmd = rs.getMetaData();
            //获取结果集的列数
            int columnCount = rsmd.getColumnCount();
            //6.解析rs
            if(rs.next()){
                T entity = (T)entityClass.newInstance();

                for(int i = 0 ; i<columnCount;i++){
                    String columnName = rsmd.getColumnName(i+1);            //fid   fname   price
                    Object columnValue = rs.getObject(i+1);     //33    苹果      5
                    setValue(entity,columnName,columnValue);
                }
                return entity ;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } finally {
            close(rs,psmt,conn);
        }
        return null ;
    }


    //执行查询，返回List
    protected List<T> executeQuery(String sql , Object... params){
        List<T> list = new ArrayList<>();
        try {
            conn = getConn() ;
            psmt = conn.prepareStatement(sql);
            setParams(psmt,params);
            rs = psmt.executeQuery();

            //通过rs可以获取结果集的元数据
            //元数据：描述结果集数据的数据 , 简单讲，就是这个结果集有哪些列，什么类型等等

            ResultSetMetaData rsmd = rs.getMetaData();
            //获取结果集的列数
            int columnCount = rsmd.getColumnCount();
            //6.解析rs
            while(rs.next()){
                T entity = (T)entityClass.newInstance();

                for(int i = 0 ; i<columnCount;i++){
                    String columnName = rsmd.getColumnName(i+1);            //fid   fname   price
                    Object columnValue = rs.getObject(i+1);     //33    苹果      5
                    setValue(entity,columnName,columnValue);
                }
                list.add(entity);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } finally {
            close(rs,psmt,conn);
        }
        return list ;
    }
}

## 5.更新addServlet文件

package com.atguigu.servlets;

import com.atguigu.servlets.dao.FruitDAO;
import com.atguigu.servlets.dao.impl.FruitDAOImpl;
import com.atguigu.servlets.pojo.Fruit;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class AddServlet extends HttpServlet {
    //doPost：響應html文件中的method="post"請求
    //request：客戶端發送的數據會包裝成request
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //getParameter：獲取數據中的參數，只能是String(若是其他類，要自行強轉)
        String fname = request.getParameter("fname");
        String priceStr = request.getParameter("price");
        Integer price = Integer.parseInt(priceStr);
        String fcountStr = request.getParameter("fcount");
        Integer fcount = Integer.parseInt(fcountStr);
        String remark = request.getParameter("remark");

        FruitDAO fruitDAO = new FruitDAOImpl();
        boolean flag = fruitDAO.addFruit(new Fruit(0,fname,price,fcount,remark));

        System.out.println(flag ? "添加成功":"添加失敗");
    }
}