Spring框架针对dao层的jdbcTemplate操作crud之query查询数据操作 —— 查询表，返回结果为某一个对象。

查询数据库表，如果用户表sw_user中存在一条username为lisi的数据，则将这条数据的对象返回

使用原始的方法，操作如下：

1、先写一个工具类，有实现MySQL数据库连接的方法，和关闭数据库连接、关闭ResultSet  结果集、关闭PreparedStatement 的方法。代码如下：

package com.swift;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {
        //连接MySQL数据库工具
        public static Connection getConn() {
            Connection conn=null;
            try {
                Class.forName("com.mysql.jdbc.Driver");
                try {
                    conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/sw_database?user=root&password=root");
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
            return conn;
        }
        //关闭数据库连接、sql连接、结果集
        public static void closeAll(Connection conn,PreparedStatement ps,ResultSet rs) {
            if(conn!=null)
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            if(ps!=null) {
                try {
                    ps.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(rs!=null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
}

使用这个DBUtil来查询数据库表中是否有一条名字为lisi的数据，将这条数据按User对象返回

package com.swift;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class QueryOneObject {

    public static User queryOneObject() {
        
        Connection conn=DBUtil.getConn();
        PreparedStatement ps=null;
        ResultSet rs=null;
        User user=null;
        try {
            ps=conn.prepareStatement("select * from sw_user where username=? and password=?");
            ps.setString(1, "lisi");
            ps.setString(2, "abcdef");
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            rs=ps.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            while(rs.next()) {
                String username=rs.getString("username");
                String password=rs.getString("password");
                user=new User(username,password);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return user;
    }
    
    
}

测试类SeverletDemo

package com.swift;

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

@WebServlet("/demo")
public class ServletDemo extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public ServletDemo() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().append("Served at: ").append(request.getContextPath());
        User user=QueryOneObject.queryOneObject();
        response.getWriter().append(user.toString());
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

结果：

---

下面将用JdbcTemplate的方法完成上面过程：

再用同样语句查询 数据库表中的zhangsan 这条记录用一个对象返回

浏览器中得到结果如上图，成功获得zhansan对象

在JdbcTemplateDemo类中增加查询返回一个对象的方法queryOneObject()

数据源DriverManagerDataSource不变

jdbcTemplate的方法有所改变，使用queryForObject(sql, new MyRowMapper(), "zhangsan","123456");

其中第二个参数是一个接口RowMapper<User>的实现类，可以使用匿名内部类，我使用的是单独的类MyRowMapper的对象

它要实现重载的方法mapRow(ResultSet rs, int num)只做两件事

一用ResultSet得到所需User对象数据

二用User进行封装得到对象并返回

package com.swift;

import java.sql.ResultSet;
import java.sql.SQLException;

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.stereotype.Component;

@Component(value="jdbcTemplateDemo")
public class JdbcTemplateDemo {
    
    public User queryOneObject() {
        
        DriverManagerDataSource dataSource=new DriverManagerDataSource();
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/sw_database");
        dataSource.setUsername("root");
        dataSource.setPassword("root");
        
        JdbcTemplate jdbcTemplate=new JdbcTemplate(dataSource);
        String sql="select * from sw_user where username=? and password=?";
        User user=jdbcTemplate.queryForObject(sql, new MyRowMapper(), "zhangsan","123456");
        return user;
        
    }
    
    public boolean delete(String username) {
    DriverManagerDataSource dataSource=new DriverManagerDataSource();
    dataSource.setDriverClassName("com.mysql.jdbc.Driver");
    dataSource.setUrl("jdbc:mysql://localhost:3306/sw_database");
    dataSource.setUsername("root");
    dataSource.setPassword("root");
    
    JdbcTemplate jdbcTemplate=new JdbcTemplate(dataSource);
    int count=jdbcTemplate.update("delete from sw_user where username=?", username);
    if(count!=0) {
        return true;
    }
    return false;
    }
}

//没有用匿名内部类，注意MyRowMapper后没有<User>

class MyRowMapper implements RowMapper<User> {

    @Override
    public User mapRow(ResultSet rs, int num) throws SQLException {
        
        String username=rs.getString("username");
        String password=rs.getString("password");
        User user=new User(username,password);
        return user;
    }
    
}

实现结果的Servlet类

package com.swift;

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

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

@WebServlet("/demo")
public class ServletDemo extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public ServletDemo() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().append("Served at: ").append(request.getContextPath());
        User user=QueryOneObject.queryOneObject();
        response.getWriter().append(user.toString());
        
        //使用JdbcTemplat的queryForObject方法
        ApplicationContext context=new ClassPathXmlApplicationContext("aop.xml");
        JdbcTemplateDemo jdbcTemplateDemo=(JdbcTemplateDemo) context.getBean("jdbcTemplateDemo");
        User user1=jdbcTemplateDemo.queryOneObject();
        response.getWriter().println();
        response.getWriter().append(user1.toString());
        
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

扫描注解的xml配置文件代码：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
         http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
    <!-- 开启注解扫描——对象和属性 -->
    <context:component-scan base-package="com.swift"></context:component-scan>
    <!-- 开启aop注解方法 -->
    <aop:aspectj-autoproxy></aop:aspectj-autoproxy>
    
</beans>

日志文件log4j.properties，运行代码能够看清Spring配置文件执行细节

代码如下：

#日志框架

#最早是System.out.print

#org.apache.log4j.Logger

#org.apache.commons.logging.Log

#java.util.logging.Logger

#org.slf4j.Logger 面向接口编程，选择实现（选择都使用这个）

#日志等级

#TRACE：详细等级，堆栈信息

#debug：类似于System.out.print

#info：类似于Hibernate的show_sql

#warn：不影响运行， 只是提示

#error：出现异常

#全局日志等级配置,输出位置

log4j.rootLogger=info,stdout,logfile

#stdout控制器

log4j.appender.stdout=org.apache.log4j.ConsoleAppender

log4j.appender.stdout.Target=System.out

log4j.appender.stdout.layout=org.apache.log4j.PatternLayout

#输出格式

log4j.appender.stdout.layout.ConversionPattern=%d %p [%c]:%L - %m%n

#文件路径输出

log4j.appender.logfile=org.apache.log4j.RollingFileAppender

#默认输出到tomcat的根路径或者运行测试工程的根路径

log4j.appender.logfile.File=pss.log

log4j.appender.logfile.MaxFileSize=512KB

# Keep three backup files.

log4j.appender.logfile.MaxBackupIndex=3

# Pattern to output: date priority [category] - message

log4j.appender.logfile.layout=org.apache.log4j.PatternLayout

log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n

#局部日志等级:就近原则

#log4j.logger.固定，后面添加想那个包使用不一样的日志等级

#log4j.logger.cn.itsource.pss=debug