最最基础Java后端

最最基础Java后端

最最基础的Java后端，仅供了解后端运作的过程，里面的方法和套路拿来就能实现一个Java后端，但深入需要学习额外的知识，比如Servlet和JDBC，文中除Java基础知识外，只涉及这两方面的知识，学习了Servlet和JDBC之后，可以了解Java后端的运作过程，对学习Spring和Mybatis等知识都有帮助

整体理解

Servlet

过程已经在图中展示出来，这里直接贴出代码实现，里面有详细的注释

Servlet代码：

public class SearchServlet extends HttpServlet {

    public SearchServlet(){
        super();
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //获取名称,使用getParameter获取URL中对应的键值对
        //如url=http:xxx/xxx?name=hello ，那么这里获取出来的name就是hello
        String name = req.getParameter("name");
        System.out.println("name = " + name);
        Gson gson = new Gson();
        List<Rubbish> Rubbishes = null;
        try {
            //分发任务，使用Dao中的方法，Rubbishes就是从数据库中返回的结果
            Rubbishes = new SearchDao().findRubbish(name);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        //将数据转换为json返回
        Type type = new TypeToken<List<Rubbish>>() {
        }.getType();
        assert Rubbishes != null;
        String jsonstr = gson.toJson(Rubbishes, type);
        resp.setContentType(jsonstr);
        resp.setCharacterEncoding("gbk");
        PrintWriter out = resp.getWriter();
        out.println(jsonstr);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        doGet(req,resp);
    }
}

web.xml

通过web.xml将对URL的访问与代码对应起来

<?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>SearchServlet</servlet-name>
        <servlet-class>com.search.servlet.SearchServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>SearchServlet</servlet-name>
        <url-pattern>/search</url-pattern>
    </servlet-mapping>
</web-app>

Domain

Domain是一个实体类，用于保存从数据库中获取的数据

public class Rubbish {
    private int kind;
    private String name;

    public int getKind() {
        return kind;
    }

    public void setKind(int kind) {
        this.kind = kind;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Dao

用于连接程序和数据库

ublic class SearchDao {

    public List<Rubbish> findRubbish(String name) throws SQLException {
        Connection conn = ConnectionUtil.open();
        //定义访问数据库的方式
        String sql = "select * from label_garbage where garbage_name like '%" + name + "%'";
        //访问数据库
        PreparedStatement pstmt = conn.prepareStatement(sql);
        ResultSet rs = pstmt.executeQuery();
        ArrayList<Rubbish>sRubbishes=new ArrayList<>();
        //获取数据库中的系列元素
        while(rs.next()){
            Rubbish aRubbish = new Rubbish();
            aRubbish.setName(rs.getString("garbage_name"));
            aRubbish.setKind(rs.getInt("garbage_kind"));
            sRubbishes.add(aRubbish);
        }
        return  sRubbishes;
    }
}

里面用到的ConnectionUtil方法，用于打开数据库

public class ConnectionUtil {
    public static Connection open() {
        // 定义连接数据库的地址以及对应的数据库，这里是访问本地的test库
        String url = "jdbc:mysql://localhost:3306/test?useSSL=false&serverTimezone=UTC";
        // 不同的数据库有着不同的driver，这里是mysql的driver
        String driver = "com.mysql.cj.jdbc.Driver";
        String username = "root";
        String password = "root";
        Connection connection = null;
        try {
            Class.forName(driver);
            System.out.println("数据库连接成功");
            connection = (Connection) DriverManager.getConnection(url, username, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return connection;

    }

    public static void close(Connection conn) {
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
                conn = null;
            }
        }
    }
}

完整的目录结构

完整的目录结构如下，有些依赖包需要你自己添加

转载：https://blog.csdn.net/weixin_42972730/article/details/105703147