新・Servlet/JSP入門編8:投稿したメッセージの削除機能の実装

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＃05:投稿したメッセージの削除機能の実装

このチャプターでは、投稿したメッセージの削除機能を実装します。

入力コード

【PostDeleteServlet】

package jp.paiza.servlet;

import java.io.*;
import java.sql.*;
import javax.sql.*;
import jakarta.annotation.*;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;
import jp.paiza.bean.*;
import jp.paiza.model.*;

@WebServlet("/post-delete")
public class PostDeleteServlet extends HttpServlet {

    @Resource(name = "jdbc/datasource")
    private DataSource ds;
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {
        
        req.setCharacterEncoding("UTF-8");

        try (Connection con = ds.getConnection()) {
            
            RequestDispatcher d = 
                req.getRequestDispatcher("/WEB-INF/jsp/post-delete.jsp");

            d.forward(req, res);
            
        } catch (SQLException e) {
            throw new ServletException(e);
        }
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {

        req.setCharacterEncoding("UTF-8");

        try (Connection con = ds.getConnection()) {
            
            RequestDispatcher d = 
                req.getRequestDispatcher("/posts");
            d.forward(req, res);
            
        } catch (SQLException e) {
            throw new ServletException(e);
        }
    }
}

【post-delete.jsp】

<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="c" uri="jakarta.tags.core" %>
<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>投稿削除</title>
    <link rel="stylesheet" href="css/style.css" type="text/css">
</head>
<body>

    <jsp:include page="header.jsp" />

    <div class="page-background">
        <div class="form-container">
            <form action="/learning/post-delete" method="post">
                <div class="user-info"><c:out value="${account.userId}" /></div>
                <textarea 
                    id="post-content" 
                    name="content" 
                    rows="4" 
                    placeholder="いまどうしてる？" disabled>${post.content}</textarea>
                <div class="form-actions">
                    <button type="submit">削除する</button>
                </div>
                <input type="hidden" id="id" name="id" value="${post.id}" />
            </form>
        </div>
    </div>
</body>
</html>

【PostModel.delete】

    public void delete(PostBean post) throws SQLException {
        String sql = "delete from posts where id = ? and account_id = ?";

        try (PreparedStatement query = con.prepareStatement(sql)) {
            
        }
    }

完成コード

【PostModel】

package jp.paiza.model;

import java.util.*;
import java.time.*;
import jp.paiza.bean.*;
import java.sql.*;
import jp.paiza.bean.AccountBean;

public class PostModel {

    private Connection con;

    public PostModel(Connection con) {
        this.con = con;
    }
    
    public List<PostBean> findAll() throws SQLException {
        String sql = "select posts.id, posts.account_id, accounts.user_id, posts.content, posts.created_at, posts.updated_at from posts inner join accounts on posts.account_id = accounts.id order by posts.id desc";
        
        ArrayList<PostBean> l = new ArrayList<>();
        try (PreparedStatement query = con.prepareStatement(sql)) {
            ResultSet rs = query.executeQuery();
            while (rs.next()) {
                PostBean post = new PostBean();
                post.setId(rs.getInt("id"));
                post.setAccountId(rs.getInt("account_id"));
                post.setUserId(rs.getString("user_id"));
                post.setContent(rs.getString("content"));
                post.setCreatedAt(rs.getTimestamp("created_at"));
                post.setUpdatedAt(rs.getTimestamp("updated_at"));
                l.add(post);
            }
        } 
        return l;
    }
    
    public void insert(PostBean post) throws SQLException {
        String sql = "insert into posts (account_id, content) VALUES (?, ?)";
        
        try (PreparedStatement query = con.prepareStatement(sql)) {
            query.setInt(1, post.getAccountId());
            query.setString(2, post.getContent());
            query.executeUpdate();
        }
    }
    
    public PostBean find(PostBean post) throws SQLException {
        String sql = "select posts.id, posts.account_id, accounts.user_id, posts.content, posts.created_at, posts.updated_at from posts inner join accounts on posts.account_id = accounts.id where posts.id = ? and account_id = ?";
        
        try (PreparedStatement query = con.prepareStatement(sql)) {
            query.setInt(1, post.getId());
            query.setInt(2, post.getAccountId());
            ResultSet rs = query.executeQuery();
            if (rs.next()) {
                PostBean p = new PostBean();
                p.setId(rs.getInt("id"));
                p.setAccountId(rs.getInt("account_id"));
                p.setUserId(rs.getString("user_id"));
                p.setContent(rs.getString("content"));
                p.setCreatedAt(rs.getTimestamp("created_at"));
                p.setUpdatedAt(rs.getTimestamp("updated_at"));
                return p;
            }
        }
        throw new SQLException("postが存在しない");
    }
    
    public void update(PostBean post) throws SQLException {
        String sql = "update posts set content = ? where id = ? and account_id = ?";

        try (PreparedStatement query = con.prepareStatement(sql)) {
            query.setString(1, post.getContent());
            query.setInt(2, post.getId());
            query.setInt(3, post.getAccountId());
            query.executeUpdate();
        } 
    }
    
    public void delete(PostBean post) throws SQLException {
        String sql = "delete from posts where id = ? and account_id = ?";
        
        try (PreparedStatement query = con.prepareStatement(sql)) {
            query.setInt(1, post.getId());
            query.setInt(2, post.getAccountId());
            query.executeUpdate();
        } 
    }
}

【PostDeleteServlet】

package jp.paiza.servlet;

import java.io.*;
import java.sql.*;
import javax.sql.*;
import jakarta.annotation.*;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;
import jp.paiza.bean.*;
import jp.paiza.model.*;

@WebServlet("/post-delete")
public class PostDeleteServlet extends HttpServlet {

    @Resource(name = "jdbc/datasource")
    private DataSource ds;
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {
        
        req.setCharacterEncoding("UTF-8");

        try (Connection con = ds.getConnection()) {

            int id = Integer.parseInt(req.getParameter("id"));
            AccountBean account = (AccountBean) req.getSession().getAttribute("account");
            
            PostBean post = new PostBean();
            post.setId(id);
            post.setAccountId(account.getId());
            
            PostModel m = new PostModel(con);
            req.setAttribute("post", m.find(post));
            
            RequestDispatcher d = 
                req.getRequestDispatcher("/WEB-INF/jsp/post-delete.jsp");

            d.forward(req, res);
            
        } catch (SQLException e) {
            throw new ServletException(e);
        }
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {

        req.setCharacterEncoding("UTF-8");

        try (Connection con = ds.getConnection()) {

            int id = Integer.parseInt(req.getParameter("id"));
            AccountBean account = (AccountBean) req.getSession().getAttribute("account");
            
            PostBean post = new PostBean();
            post.setId(id);
            post.setAccountId(account.getId());
            
            PostModel m = new PostModel(con);
            m.delete(post);
            
            RequestDispatcher d = 
                req.getRequestDispatcher("/posts");
            d.forward(req, res);
            
        } catch (SQLException e) {
            throw new ServletException(e);
        }
    }
}

公式リファレンス

インタフェースConnection
https://docs.oracle.com/javase/jp/17/docs/api/java.sql/java/sql/Connection.html

インタフェースPreparedStatement
https://docs.oracle.com/javase/jp/17/docs/api/java.sql/java/sql/PreparedStatement.html

インタフェースResultSet
https://docs.oracle.com/javase/jp/17/docs/api/java.sql/java/sql/ResultSet.html

クラスSQLException
https://docs.oracle.com/javase/jp/17/docs/api/java.sql/java/sql/SQLException.html

Class HttpServlet
https://jakarta.ee/specifications/servlet/6.1/apidocs/jakarta.servlet/jakarta/servlet/http/httpservlet

Interface HttpServletRequest
https://jakarta.ee/specifications/servlet/6.1/apidocs/jakarta.servlet/jakarta/servlet/http/httpservletrequest

Interface HttpServletResponse
https://jakarta.ee/specifications/servlet/6.1/apidocs/jakarta.servlet/jakarta/servlet/http/httpservletresponse

Interface HttpSession
https://jakarta.ee/specifications/servlet/6.1/apidocs/jakarta.servlet/jakarta/servlet/http/httpsession

プログラミング学習 > 新・Servlet/JSP入門編 > 新・Servlet/JSP入門編8: CRUD機能を作成しよう > 投稿したメッセージの削除機能の実装

新・Servlet/JSP入門編8: CRUD機能を作成しよう

＃05:投稿したメッセージの削除機能の実装

入力コード

完成コード

関連講座

公式リファレンス