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手写orm框架
2022-07-24 05:15:00 【x0757】
目录
大致框架
1.建立框架
首先创建一个Maven项目, 在引用第三方依赖
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.24</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.29</version>
</dependency>
</dependencies>2.新增一个类
@Data
//注解
@TableName(value = "tb_dept")
public class Dept {
//注解
@TableId(value = "id")
public Integer id;
//注解
@TableFiled(value = "deptname")
public String name;
public String address;
}
3.添加一个dao包
//继承BaseDao
public class DeptDao extends BaseDao<Dept> {
}4.添加注解
//作用在属性上
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface TableFiled {
String value();
}
//作用在类上
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface TableName {
String value();
}
//作用在属性上
@Target(value = ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface TableId {
String value() default "id";
}5.连接数据库
5.1创建一个db.properties文件
jdbc.driverName=com.mysql.cj.jdbc.Driver
jdbc.url = jdbc:mysql://localhost:3306/数据库名?serverTimezone=Asia/Shanghai
jdbc.username =root
jdbc.password = 数据库密码5.2创建DBUtils类
public class DBUtils {
private static String driverName;
private static String url;
private static String username;
private static String password;
//建立连接
static {
try {
Properties properties = new Properties();
properties.load(new FileInputStream("db.properties"));
driverName = properties.getProperty("jdbc.driverName");
url = properties.getProperty("jdbc.url");
username = properties.getProperty("jdbc.username");
password = properties.getProperty("jdbc.password");
}catch (Exception e){
e.printStackTrace();
}
}
public static Connection getConn() throws Exception{
Class.forName(driverName);
Connection connection = DriverManager.getConnection(url,username,password);
return connection;
}
//关闭资源
public static void closeAll(ResultSet rs, PreparedStatement ps,Connection connection){
try {
if(rs!=null){
rs.close();
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}
try {
if(ps!=null){
ps.close();
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}
try {
if(connection!=null){
connection.close();
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
6.创建BaseDao类实现增删改查（CRUD）
package com.xzj.util;
import com.xzj.annotation.TableId;
import com.xzj.annotation.TableFiled;
import com.xzj.annotation.TableName;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
public class BaseDao<T>{
private PreparedStatement ps;
private ResultSet rs;
private Connection connection;
private Class<?> clazz;
public BaseDao(){
//this对应子类对象 获取当前类反射类对象
Class<? extends BaseDao> aClass = this.getClass();
//获取当前反射类的父类---包含父类的泛型
ParameterizedType genericSuperclass = (ParameterizedType) aClass.getGenericSuperclass();
//获取泛型的反射类
Type[] actualTypeArguments = genericSuperclass.getActualTypeArguments();
clazz= (Class<?>) actualTypeArguments[0];
}
//根据id查询
public Object findId(Object id){
try{
StringBuffer sb= new StringBuffer();
sb.append("select * from ");
TableName tableNameAnnotation = clazz.getAnnotation(TableName.class);
String tableName="";
if(tableNameAnnotation!=null){
tableName=tableNameAnnotation.value();
}else{
tableName= clazz.getSimpleName();
}
sb.append(tableName+" where ");
Field[] declaredFields = clazz.getDeclaredFields();
boolean flag = false;
for (Field declaredField : declaredFields) {
declaredField.setAccessible(true);
TableId annotation = declaredField.getAnnotation(TableId.class);
if (annotation != null) {
sb.append(annotation.value() + "='" + id + "'");
flag = true;
break;
}
}
if (flag == false) {
throw new RuntimeException("No primary key annotation added");
}
System.out.println(sb);
Connection conn = DBUtils.getConn();
PreparedStatement ps = conn.prepareStatement(sb.toString());
ResultSet rs = ps.executeQuery();
while (rs.next()){
Object o = clazz.newInstance();
Field[] declaredFields1 = clazz.getDeclaredFields();
for (Field field : declaredFields1) {
field.setAccessible(true);
TableFiled annotation = field.getAnnotation(TableFiled.class);
if(annotation!=null){
field.set(o,rs.getObject(annotation.value()));
}else{
field.set(o,rs.getObject(field.getName()));
}
}
return o;
}
}catch (Exception e){
e.printStackTrace();
}finally {
DBUtils.closeAll(rs,ps,connection);
}
return null;
}
//查询所有
public List<T> fandAll(){
List<T> list = new ArrayList<T>();
try {
StringBuffer sb = new StringBuffer();
sb.append("select * from ");
//获取表名
TableName tableNameAnnotation = clazz.getAnnotation(TableName.class);
String tableName = "";
if (tableNameAnnotation != null) {
tableName = tableNameAnnotation.value();
} else {
tableName = clazz.getSimpleName();
}
sb.append(tableName);
Connection conn =DBUtils.getConn();
PreparedStatement ps = conn.prepareStatement(sb.toString());
ResultSet rs = ps.executeQuery();
while (rs.next()){
Object o = clazz.newInstance();
Field[] declaredFields = clazz.getDeclaredFields();
for (Field declaredField : declaredFields) {
declaredField.setAccessible(true);
TableFiled tableFiled = declaredField.getAnnotation(TableFiled.class);
if(tableFiled!=null){
declaredField.set(o,rs.getObject(tableFiled.value()));
}else {
declaredField.set(o,rs.getObject(declaredField.getName()));
}
}
list.add((T) o);
}
}catch (Exception e){
e.printStackTrace();
}
return list;
}
//删除
public int delete(Object id){
try {
StringBuffer sb = new StringBuffer();
sb.append("delete from ");
// 获取表名
TableName tableNameannotation = clazz.getAnnotation(TableName.class);
String tableName = "";
//获取类上的注解
if (tableNameannotation != null) {
tableName = tableNameannotation.value();
} else {
tableName = clazz.getSimpleName();
}
Field[] declaredFields = clazz.getDeclaredFields();
boolean flag = false;
sb.append(tableName+" where ");
for (Field declaredField : declaredFields) {
declaredField.setAccessible(true);
TableId annotation = declaredField.getAnnotation(TableId.class);
if (annotation != null) {
sb.append(annotation.value() + "='" + id + "'");
flag = true;
break;
}
}
if (flag == false) {
throw new RuntimeException("No primary key annotation added");
}
System.out.println(sb);
Connection conn = DBUtils.getConn();
PreparedStatement ps = conn.prepareStatement(sb.toString());
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}finally {
DBUtils.closeAll(rs,ps,connection);
}
return 0;
}
//根据主键修改
public int update(T t){
try {
StringBuffer sb = new StringBuffer();
sb.append("update ");
//得到T的反射类
Class<?> aClass = t.getClass();
//获取类上的注解
TableName tableNameannotation = aClass.getAnnotation(TableName.class);
String tableName ="";
if (tableNameannotation != null) {
tableName = tableNameannotation.value();
} else {
tableName = aClass.getSimpleName();
}
sb.append(tableName+" set ");
boolean flag=false;
Field[] declaredFields = aClass.getDeclaredFields();
String where = "where";
for (Field field : declaredFields) {
TableId annotation = field.getAnnotation(TableId.class);
if (annotation != null) {
flag=true;
where += " "+annotation.value() + "=" + field.get(t);
}else {
TableFiled tableField = field.getAnnotation(TableFiled.class);
if(tableField!=null){
sb.append(tableField.value()+"='"+field.get(t)+"',");
}else{
sb.append(field.getName()+"='"+field.get(t)+"',");
}
}
}
if(flag==false){
throw new Exception("No primary key annotation added");
}
String str = sb.substring(0, sb.lastIndexOf(","));
String sql = str+where;
System.out.println(sql);
Connection conn = DBUtils.getConn();
PreparedStatement ps = conn.prepareStatement(sql.toString());
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}finally {
DBUtils.closeAll(rs,ps,connection);
}
return 0;
}
//添加
public int insert(T t){
try{
StringBuffer sb = new StringBuffer("insert into ");
Class<?> aClass = t.getClass();
TableName annotation = aClass.getAnnotation(TableName.class);
String tableName ="";
if(annotation!=null){
tableName = annotation.value();
}else {
tableName = aClass.getSimpleName();
}
sb.append(tableName);
System.out.println(sb);
Field[] declaredFields = aClass.getDeclaredFields();
List<String> columns = new ArrayList<>();
List<String> values = new ArrayList<>();
for (Field declaredField:declaredFields){
declaredField.setAccessible(true);
TableFiled tableField = declaredField.getAnnotation(TableFiled.class);
if(tableField!=null){
columns.add(tableField.value());
}else {
columns.add(declaredField.getName());
}
values.add("'"+declaredField.get(t)+"'");
}
sb.append(columns.toString().replace("[","(").replace("]",")"));
sb.append(" values ");
sb.append(values.toString().replace("[","(").replace("]",")"));
System.out.println(sb);
Connection conn = DBUtils.getConn();
PreparedStatement ps = conn.prepareStatement(sb.toString());
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}finally {
DBUtils.closeAll(rs,ps,connection);
}
return 0;
}
}
7.测试
public class Test {
public static void main(String[] args) {
DeptDao deptDao = new DeptDao();
//查询所有
System.out.println(deptDao.fandAll());
//根据id查询
System.out.println(deptDao.findId(3));
//删除
deptDao.delete(2);
Dept dept = new Dept();
//修改
dept.setId(12);
dept.setName("王");
dept.setAddress("杭州");
deptDao.update(dept);
//添加
dept.setName("xyang");
dept.setAddress("北京");
deptDao.insert(dept);
}
}
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