本文主要讲述DAO层，数据访问对象的含义与使用
一. 图解DAO层
二. 代码结构
1. dao
2. domain
3. utils
4.test做测试
三. 具体实现
1.1 dao中的BasicDAO
/**
* 处理sql语句，返回结果
*/
public class BasicDAO<T> {
private QueryRunner queryRunner = new QueryRunner();
private Connection connection;
/**
*
* @param sql sql语句
* @param aClass aClass反射对象
* @param params params可变参数，对?赋值
* @return
*/
// 查询多行结果
// 方法中的泛型，必须是类中声明过的，没有声明的不能使用。
public List<T> queryMultiple(String sql, Class<T> aClass, Object... params){
List<T> result = null;
try {
connection = JDBCUtilsByDruid.getConnection();
result = queryRunner.query(connection,sql, new BeanListHandler<T>(aClass), params);
} catch (SQLException e) {
throw new RuntimeException(e); // 方法默认抛出运行时异常机制
} finally {
JDBCUtilsByDruid.Close(null,null,connection);
}
return result;
}
// 查询单行数据
public T querySingle(String sql,Class<T> aClass,Object... params){
T t = null;
try {
connection = JDBCUtilsByDruid.getConnection();
System.out.println("@2:" + connection);
t = queryRunner.query(connection,sql,new BeanHandler<T>(aClass),params);
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtilsByDruid.Close(null,null,connection);
}
return t;
}
// 查询单行单列的数据
public Object queryScalar(String sql,Object... params){
Object obj = null;
try {
connection = JDBCUtilsByDruid.getConnection();
obj = queryRunner.query(connection, sql, new ScalarHandler(), params);
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
JDBCUtilsByDruid.Close(null,null,connection);
}
return obj;
}
// 执行DML语句
public int update(String sql,Object...params){
int update = 0;
try {
connection = JDBCUtilsByDruid.getConnection();
update = queryRunner.update(connection,sql, params);
} catch (SQLException e) {
new RuntimeException(e);
} finally {
JDBCUtilsByDruid.Close(null,null,connection);
}
return update;
}
}
注意：这里的泛型使用，方法中所使用的泛型，必须是在该类中实现声明的，如：
BasicDAO类声明泛型T
public class BasicDAO<T> {}
BasicDAO类的方法使用泛型T
ublic List<T> queryMultiple(String sql, Class<T> aClass, Object... params){}
1.2 dao中的AdminDAO
public class AdminDAO extends BasicDAO<Admin> {
// 1.继承BasicDAO的所有方法
// 2.可以写特有的方法
}
2 domain中的Admin
public class Admin {
private Integer id;
private String name;
private String pwd;
public Admin() {
}
public Admin(Integer id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPwd() {
return pwd;
}
public void setPwd(String pwd) {
this.pwd = pwd;
}
@Override
public String toString() {
return "Admin{" +
"id=" + id +
", name='" + name + '\'' +
", pwd='" + pwd + '\'' +
'}';
}
}
注意：domain中的类的无参构造器不能省略【反射机制】
3. utils中的 JDBCUtilsByDruid
public class JDBCUtilsByDruid {
private static DataSource druid;
static {
Properties properties = new Properties();
try {
properties.load(new FileInputStream("src\\druid.properties"));
druid = DruidDataSourceFactory.createDataSource(properties);
} catch (Exception e) {
e.printStackTrace();
}
}
public static Connection getConnection(){
Connection connection = null;
try {
connection = druid.getConnection();
} catch (SQLException e) {
e.printStackTrace();
}
return connection;
}
@SuppressWarnings({"all"})
public static boolean Close(ResultSet resultSet, Statement statement,Connection connection){
try {
if(resultSet != null){
resultSet.close();
}
if(statement != null){
statement.close();
}
if(connection != null){
connection.close();
}
} catch (SQLException e) {
throw new RuntimeException();
}
return true;
}
}
参看 jdbc+Druid工具类 - zwGitOne - 博客园 (cnblogs.com)这篇博客
4. test测试
public class TestDAO {
@Test
public void testAdmin(){
// 1.查询多行记录
String all = "select * from admin ";
AdminDAO adminDAO = new AdminDAO();
List<Admin> adminList = adminDAO.queryMultiple(all, Admin.class, null);
System.out.println("===显示表中所有的数据===");
Iterator<Admin> iterator = adminList.iterator();
while (iterator.hasNext()) {
Admin admin = iterator.next();
System.out.println(admin);
}
// 2.查询单行记录
String single = "select * from admin where id = ?";
Admin admin = adminDAO.querySingle(single, Admin.class, 8);
System.out.println("===显示单行对象===");
System.out.println(admin);
// 3.查询单行单个对象
String scalar = "select name from admin where id = ?";
int id = 8;
Object o = adminDAO.queryScalar(scalar, id);
System.out.println("===显示单行单个对象===");
System.out.println("id:" + id + "的name是" + o);
// 增加
String insert = "insert into admin values(null,?,?)";
int row = adminDAO.update(insert, "张山峰", "123456");
// 修改
String update = "update admin set name = ? where id = ?";
row = adminDAO.update(update, "张三丰", 16);
// 删除
String delete = "delete from admin where id = ?";
row = adminDAO.update(delete,16);
}
}
运行结果如下：
===显示表中所有的数据===
Admin{id=3, name='Tom3', pwd='123'}
Admin{id=5, name='Tom2', pwd='123'}
Admin{id=6, name='Tom3', pwd='123'}
Admin{id=8, name='Tom2', pwd='123'}
Admin{id=9, name='Tom3', pwd='123'}
Admin{id=11, name='zw', pwd='123'}
Admin{id=12, name='郑为', pwd='1234'}
Admin{id=13, name='郑威', pwd='1234'}
Admin{id=14, name='郑为', pwd='1234'}
Admin{id=15, name='郑威', pwd='1234'}
Admin{id=17, name='张山峰', pwd='123456'}
Admin{id=18, name='张山峰', pwd='123456'}
Admin{id=19, name='张山峰', pwd='123456'}
Admin{id=20, name='张山峰', pwd='123456'}
@2:com.mysql.cj.jdbc.ConnectionImpl@10aa41f2
===显示单行对象===
Admin{id=8, name='Tom2', pwd='123'}
===显示单行单个对象===
id:8的name是Tom2
Process finished with exit code 0
View Code
四. 总结
理解AdminDAO与BasicDAO的继承关系，为什么抽象出BasicDAO这一父类？
将XXxxDAO类的公共操作提取出来，作为父类BasicDAO，使得XXxxDAO代码简化。
标签：name,对象,DAO,public,访问,pwd,Admin,id,String From： https://www.cnblogs.com/zwgitOne123/p/17084341.html