1. Preparation
1. Create a new folder lib, copy the JDBC.jar package, and right-click Build Path;
2. Right-click the project name Build Path-> Add Bilrary->JUnit->JUnit (function: unit test test code block);
2. Write code, use Dao mode
The difference between using PreparedStatement and using Statement to compile SQL statements:
Statement : First splicing SQL statements.If the variable contains a database keyword , it is considered to be a keyword, not an ordinary string.
PreparedStatement: Pre-process the given SQL statement, perform syntax checking on it, and use the? Placeholder in the SQL statement to replace the variable value to be passed in later, it will be treated as a string, and no keywords will be generated .(recommend)
package com.itheima.dao;
public interface UserDao {
/**
* 查询所有
*/
void findALL();
/**
* 添加记录
*/
void insert(int cid,String cname,String cdesc);
/**
* 更新数据
*/
void upstate(int cid,String cname);
/**
* 删除记录
*/
void delete(int cid);
}package com.itheima.dao.impl;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import com.itheima.dao.UserDao;
import com.itheima.util.JDBCUtil;
public class UserDaoImpl implements UserDao{
@Override
public void findALL() {
//注册驱动 建立连接
Connection conn = null;
//创建PreparedStatement
PreparedStatement pst = null;
//得到Result
ResultSet rs = null;
try {
conn = JDBCUtil.getConn();
String sql = "select * from category"; //category是我数据库的表名,下同
pst = conn.prepareStatement(sql);
rs = pst.executeQuery();
while(rs.next()) {
int cid = rs.getInt("cid"); //cid表的列名,下同
String cname = rs.getString("cname"); //cname表的列名,下同
String cdesc = rs.getString("cdesc"); //cdesc表的列名,下同
System.out.println(cid+"-"+cname+"-"+cdesc);
}
}catch(Exception e) {
e.printStackTrace();
}finally {
JDBCUtil.release(conn, pst, rs);
}
}
@Override
public void insert(int cid, String cname, String cdesc) {
//注册驱动 建立连接
Connection conn =null;
//创建PreparedStatement
PreparedStatement pst = null;
try {
conn = JDBCUtil.getConn();
String sql = "insert into category values(?,?,?)";
pst = conn.prepareStatement(sql);
pst.setInt(1, cid);
pst.setString(2, cname);
pst.setString(3, cdesc);
int result = pst.executeUpdate();
if(result>0) {
System.out.println("插入成功");
}else {
System.out.println("插入失败");
}
}catch(Exception e) {
e.printStackTrace();
}finally {
JDBCUtil.release(conn, pst);
}
}
@Override
public void upstate(int cid, String cname) {
//注册驱动 建立连接
Connection conn = null;
//创建PreparedStatement
PreparedStatement ps = null;
try {
conn = JDBCUtil.getConn();
String sql = "update category set cid=? where cname=?";
ps = conn.prepareStatement(sql);
ps.setInt(1, cid);
ps.setString(2, cname);
int result = ps.executeUpdate();
if(result>0) {
System.out.println("更新成功");
}else {
System.out.println("更新失败");
}
}catch(Exception e) {
e.printStackTrace();
}finally {
JDBCUtil.release(conn, ps);
}
}
@Override
public void delete(int cid) {
//注册驱动 建立连接
Connection conn =null;
//创建PreparedStatement
PreparedStatement ps = null;
try {
conn = JDBCUtil.getConn();
String sql = "delete from category where cid=?";
ps = conn.prepareStatement(sql);
ps.setInt(1, cid);
int result = ps.executeUpdate();
if(result>0) {
System.out.println("删除成功");
}else {
System.out.println("删除失败");
}
}catch(Exception e) {
e.printStackTrace();
}finally{
JDBCUtil.release(conn, ps);
}
}
}package com.itheima.test;
import org.junit.Test;
import com.itheima.dao.UserDao;
import com.itheima.dao.impl.UserDaoImpl;
public class TestUserDaoImpl {
@Test
public void testFindAll() {
UserDao u1 = new UserDaoImpl();
u1.findALL();
}
@Test
public void testInsert() {
UserDao u1 = new UserDaoImpl();
u1.insert(6, "手环戒指", "金戒指,银项链");
}
@Test
public void testUpadate() {
UserDao u1 = new UserDaoImpl();
u1.upstate(6, "电脑办公");
}
@Test
public void testUpdate(){
UserDao u1 = new UserDaoImpl();
u1.delete(6);
}
}package com.itheima.util;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
public class JDBCUtil {
static String url = null;
static String user = null;
static String password=null;
static {
InputStream inStream = null;
//注册驱动 建立连接
try {
Properties properties = new Properties();
//文件在src里
inStream = JDBCUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");
//导入输入流
properties.load(inStream);
//读取属性
url = properties.getProperty("url");
user = properties.getProperty("user");
password = properties.getProperty("password");
} catch (Exception e) {
e.printStackTrace();
}finally {
try {
if(null!=inStream) {
inStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}finally {
inStream = null;
}
}
}
public static Connection getConn() {
Connection conn = null;
try {
conn = DriverManager.getConnection(url, user, password);
return conn;
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
/**
* 释放资源
* @param conn
* @param st
* @param rs
*/
public static void release(Connection conn,Statement st,ResultSet rs) {
closeConn(conn);
closeSt(st);
closeRs(rs);
}
public static void release(Connection conn,Statement st) {
closeConn(conn);
closeSt(st);
}
private static void closeConn(Connection conn){
try {
if(null!=conn) {
conn.close();
}
}catch(Exception e) {
e.printStackTrace();
}finally {
conn = null;
}
}
private static void closeSt(Statement st){
try {
if(null!=st) {
st.close();
}
}catch(Exception e) {
e.printStackTrace();
}finally {
st = null;
}
}
private static void closeRs(ResultSet rs){
try {
if(null!=rs) {
rs.close();
}
}catch(Exception e) {
e.printStackTrace();
}finally {
rs = null;
}
}
}//jdbj.properties文件内容
url=jdbc:mysql://localhost/day06?serverTimezone=UTC //day06是数据库名
user=root //root数据库登录名
password=123456 //123456登录密码Three. Product carefully