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Spring之DAO一

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11/25
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前面博客把bean、aop简单了解了一下，今天主要是了解Spring中DAO层，如果使用传统的JDBC时需要创建连接、打开、执行sql、关闭连接这一系列的步骤，Spring框架对JDBC进行了封装，我们只需使用封装好的JdbcTemplate执行sql语句。主要还是继承了Spring提供的JdbcDaoSupport。下面主要是用来演示怎么使用JdbcDaoSupport。

一、创建Model

这里创建一个User类，作为model。 

package Cuiyw.Spring.Model;

public class User {

    private int userId;

    public int getUserId() {

        return userId;

    }

    public void setUserId(int userId) {

        this.userId = userId;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    private String name;

    private float money;

    public float getMoney() {

        return money;

    }

    public void setMoney(float money) {

        this.money = money;

    }

}

二、创建DAO接口并实现接口

1.这里创建IUserDAO接口，声明了两个方法，一个是获取所有的User，一个是新增User。 

package Cuiyw.Spring.IDao;

import java.util.*;

import Cuiyw.Spring.Model.User;

public interface IUserDAO {

    public List<User>QueryAllUser();

    public Boolean AddUser(String name,float money);

}

2.这里实现接口IUserDAO,并且继承JdbcDaoSupport。在下面的代码中能找到getJdbcTemplate()，其实我们右键选择Open declaration 时可以定位到抽象类JdbcDaoSupport，JdbcDaoSupport里面有一个JdbcTemplate属性，而且还有get或set JDBC DataSource，然后选中JdbcTemplate，再Open declaration,发现JdbcTemplate的构造函数需要DataSource，JdbcDaoSupport提供JdbcTemplate对象，并维护着JdbcTemplate对象需要的DataSource。 

package Cuiyw.Spring.Dao;

import java.util.*;

import org.springframework.jdbc.core.support.JdbcDaoSupport;

import Cuiyw.Spring.IDao.IUserDAO;

import Cuiyw.Spring.Model.User;

public class UserDAO extends JdbcDaoSupport implements IUserDAO {

    public List<User> QueryAllUser() {

        String sql="select id,name,money from tb_user";

        List<Map<String,Object>> list=getJdbcTemplate().queryForList(sql);

        List<User> userList=new ArrayList<User>();

        for(Map<String,Object> row:list)

        {

            User user=new User();

            user.setUserId((Integer)row.get("id"));

            user.setName((String)row.get("name"));

            user.setMoney((Float)row.get("money"));

            userList.add(user);

        }

        return userList;

    }

    public Boolean AddUser(String name,float money) {

        String sql="insert into tb_user (name,money) values (?,?)";

        int row=getJdbcTemplate().update(sql, new Object[]{name,money});

        if(row>0)

        {

            return true;

        }

        return false;

    }

}
    public JdbcTemplate(DataSource dataSource) {

        setDataSource(dataSource);

        afterPropertiesSet();

    }

3.上下文配置

上面DataSource从哪里来呢?就需要在上下文中配置。首先配置DataSource，然后由于UserDAO继承了抽象类JdbcDaoSupport，所以也需要设置属性dataSource 

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:context="http://www.springframework.org/schema/context"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

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/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd

">

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">

  <property name="driverClassName">

          <value>com.mysql.jdbc.Driver</value>

  </property>

  <property name="url">

          <value>jdbc:mysql://localhost:3306/spring</value>

  </property>

  <property name="username">

          <value>root</value>

  </property>

  <property name="password">

      <value>123456</value>

  </property>

</bean>

<bean id="userDao" class="Cuiyw.Spring.Dao.UserDAO" depends-on="dataSource">

    <property name="dataSource" ref="dataSource"></property>

</bean>

</beans>

4.Mysql新增数据库和表

上面2中UserDAO执行了两个sql，涉及到表tb_user，字段id、name、money。在3上下文配置mysql时指定了数据库名spring。所以按照上面的创建。

5.实验 

        ApplicationContext context=new ClassPathXmlApplicationContext(new String[]{"ApplicationContext.xml"});

        BeanFactory factory=context;

        IUserDAO userDao=(IUserDAO)factory.getBean("userDao");

        userDao.AddUser("cuiywA",888);

        userDao.AddUser("cuiywB",666);

        List<User> list=userDao.QueryAllUser();

        for(User u:list)

        {

            System.out.println("name:"+u.getName()+" money: "+u.getMoney());

        }

6.错误

在实现上面的步骤时报了好几个错误，有因为我疏忽的，还有数据类型和数据库不一直的，最重要的两个我这里也记录了下来。

1.下面的错误是由于缺少commons-dbcp.jar、commons-pool.jar导致的 

Cannot find class [org.apache.commons.dbcp.BasicDataSource] for bean with name 'dataSource' defined in class path resource [ApplicationContext.xml]; nested exception is java.lang.ClassNotFoundException: org.apache.commons.dbcp.BasicDataSource

2.还有就是我在UserDAO中继承了JdbcDaoSupport，但就是没自动提示要引入的包，这个第一次没经验，百度了才指定需要引入spring-jdbc.jar.

3.忘记引入mysql驱动 

Failed to obtain JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot load JDBC driver class 'com.mysql.jdbc.Driver'

上面的错误都是没有引入jar包，这里把pom.xml也放进来，留着以后好用。 

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <groupId>Cuiyw</groupId>

  <artifactId>SpringAop</artifactId>

  <version>0.0.1-SNAPSHOT</version>

  <packaging>jar</packaging>

  <name>SpringAop</name>

  <url>http://maven.apache.org</url>

  <properties>

    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

      <spring.version>5.0.0.RELEASE</spring.version>

  </properties>

  <dependencies>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-jdbc</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>commons-dbcp</groupId>

            <artifactId>commons-dbcp</artifactId>

            <version>1.4</version>

        </dependency>

        <dependency>

            <groupId>commons-pool</groupId>

            <artifactId>commons-pool</artifactId>

            <version>1.6</version>

        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->

        <dependency>

            <groupId>mysql</groupId>

            <artifactId>mysql-connector-java</artifactId>

            <version>5.1.6</version>

        </dependency>

        <dependency>

          <groupId>junit</groupId>

          <artifactId>junit</artifactId>

          <version>3.8.1</version>

          <scope>test</scope>

        </dependency>

            <!-- https://mvnrepository.com/artifact/aspectj/aspectjweaver -->

        <dependency>

            <groupId>aspectj</groupId>

            <artifactId>aspectjweaver</artifactId>

            <version>1.5.4</version>

        </dependency>

            <!-- https://mvnrepository.com/artifact/aspectj/aspectjrt -->

        <dependency>

            <groupId>aspectj</groupId>

            <artifactId>aspectjrt</artifactId>

            <version>1.5.4</version>

        </dependency>

  </dependencies>

</project>

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