JDBC入门

JDBC

（Java Database Connectivity） Java数据库连接，用java操作数据库的一门技术，一组规范，接口。

五个步骤

1.加载驱动

2.创建连接

3.建立通道

4.执行并返回结果集

5.关闭



一.数据库层

1.创建表

create table category(
cid number(10) primary key,
cname varchar2(100),
cdesc   varchar2(200)
)

2.创建序列

create sequence seq_category minvalue 0 start with 0 increment by 1

二.VO(Value Object)实体层

创建category类，实现getter/setter方法

public class Category {
private Integer cid;
private String  name;
private String cdesc;
}

三.连接数据库的工具类 ConnOracle

public class ConnOracle2 {

private static Connection conn;
private static final String className="oracle.jdbc.OracleDriver";
private static final String url="jdbc:oracle:thin:@localhost:1521:ORCL11";
private static final String user="scott";
private static final String password="tiger";

//1,加载驱动(可以静态加载)
static{
//oracle.jdbc.OracleDriver.class
try {
Class.forName(className);
} catch (ClassNotFoundException e) {
e.printStackTrace();
System.out.println("类没找到");
}
}

public static Connection getConnection() {
//2,创建连接
try {
conn = DriverManager.getConnection(url, user, password);
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据库连接失败!");
}

return conn;
}

public static void free(Connection conn,Statement statement,ResultSet executeQuery){
try {
if (executeQuery != null) {
executeQuery.close();
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (statement!= null) {
statement.close();
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}

}

四.DAO(Data Access Object) 数据访问层

对表的最基本的CRUD

接口：

public interface CategoryDaoImpl {
/**
* 添加一条
* @param category
*/
public void addCategory(Category category);
/**
* 更新一条
* @param category
*/
public void updateCategory(Category category);
/**
* 删除一条
* @param category
*/
public void deleteCategoryById(int id);
/**
* 查一条
* @param id
* @return
*/
public Category selecCategoryById(int id);
/**
* 查所有
* @return
*/
public List<Category> selecCategory();
}

接口的实现类

public class CategoryDao implements CategoryDaoImpl {

Connection conn = null;

public CategoryDao() {
// 3,建立通道
conn = ConnOracle2.getConnection();
}

@Override
public void addCategory(Category category) {

String sql = "INSERT INTO CATEGORY VALUES(seq_category.nextval,?,?)";

PreparedStatement prepareStatement = null;

try {
prepareStatement = conn.prepareStatement(sql);
prepareStatement.setString(1, category.getName());
prepareStatement.setString(2, category.getCdesc());

// 4,执行sql
int count = prepareStatement.executeUpdate();
if (count >= 1) {
System.out.println("插入成功！");
} else {
System.out.println("插入失败！");
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
// 5.关闭
ConnOracle2.free(conn, prepareStatement, null);
}

}

@Override
public void updateCategory(Category category) {

// 3,建立通道
String sql = "UPDATE CATEGORY SET cname=?,cdesc=? WHERE cid=?";
PreparedStatement prepareStatement = null;
try {
prepareStatement = conn.prepareStatement(sql);
prepareStatement.setString(1, category.getName());
prepareStatement.setString(2, category.getCdesc());
prepareStatement.setInt(3, category.getCid());

// 4,执行sql
int count = prepareStatement.executeUpdate();
if (count >= 1) {
System.out.println("更新成功！");
} else {
System.out.println("更新失败！");
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
// 5.关闭
ConnOracle2.free(conn, prepareStatement, null);
}
}

@Override
public void deleteCategoryById(int id) {

String sql = "DELETE FROM CATEGORY WHERE cid=?";
PreparedStatement prepareStatement = null;
try {
prepareStatement = conn.prepareStatement(sql);
prepareStatement.setInt(1, id);
// 4,执行sql
int count = prepareStatement.executeUpdate();
if (count >= 1) {
System.out.println("删除成功！");
} else {
System.out.println("删除失败！");
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
// 5.关闭
ConnOracle2.free(conn, prepareStatement, null);
}
}

@Override
public Category selecCategoryById(int id) {

String sql = "SELECT * FROM CATEGORY WHERE cid=?";
PreparedStatement prepareStatement = null;
Category category = null;
ResultSet executeQuery = null;
try {
prepareStatement = conn.prepareStatement(sql);
prepareStatement.setInt(1, id);
// 4,执行sql
executeQuery = prepareStatement.executeQuery();

if (executeQuery.next()) {
category = new Category();
category.setCid(executeQuery.getInt("cid"));
category.setName(executeQuery.getString("cname"));
category.setCdesc(executeQuery.getString("cdesc"));
}

} catch (SQLException e) {
e.printStackTrace();
} finally {
// 5.关闭
ConnOracle2.free(conn, prepareStatement, executeQuery);
}

return category;
}

@Override
public List<Category> selecCategory() {

// 3,建立通道
String sql = "SELECT * FROM CATEGORY";
PreparedStatement prepareStatement = null;
List<Category> list = new ArrayList<>();
ResultSet executeQuery = null;
try {
prepareStatement = conn.prepareStatement(sql);
// 4,执行sql
executeQuery = prepareStatement.executeQuery();

while (executeQuery.next()) {
Category category = new Category();
category.setCid(executeQuery.getInt("cid"));
category.setName(executeQuery.getString("cname"));
category.setCdesc(executeQuery.getString("cdesc"));
list.add(category);
}

} catch (SQLException e) {
e.printStackTrace();
} finally {
// 5.关闭
ConnOracle2.free(conn, prepareStatement, executeQuery);
}

return list;
}

}