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Tear the ORM framework by hand (generic + annotation + reflection)
2022-07-29 05:54:00 【Don't want bald Xiao Yang】
ORM:(Object relative Mapping) Object relational mapping framework . Help you automatically compare the records in the database with java Entity classes are mapped together .
annitation package : Custom annotation Used on entity classes
TableName: When the table name is inconsistent with the entity class name, use
TableField: When the column name and attribute name are inconsistent, use
TablePrimaryKey: Use on primary key , Used to distinguish from other attributes
package com.qy151.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* @unthor : YSH
* @date : 20:39 2022/7/14
*/
@Retention(value = RetentionPolicy.RUNTIME)
@Target(value = ElementType.TYPE)
public @interface TabelName {
String value();
}
util package : Public class
DBUtils: Get the connection object and close the connection resource
package com.qy151.util;
import java.sql.*;
/**
* @unthor : YSH
* @date : 20:06 2022/7/14
*/
/* Get the connection object and close the connection resource */
public class DBUtils {
private static String driverName="com.mysql.cj.jdbc.Driver";
private static String url="jdbc:mysql://localhost:3306/myda2?serverTimezone=Asia/Shanghai";
private static String user=" Your username ";
private static String password="";
public static Connection getCon() throws Exception {
Class.forName(driverName);
Connection connection = DriverManager.getConnection(url, user, password);
return connection;
}
public static void closeAll(ResultSet res, PreparedStatement ps,Connection connection){
try {
if(res!=null){
res.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();
}
}
}
BaseDao class : Parent class
How to get generics in class names T:
//this The corresponding subclass object Get the reflection class object of the current class
Class<? extends BaseDao> aClass = this.getClass();
// Get the parent class of the current reflection class ---- Contains generics of the parent class
ParameterizedType genericSuperclass = (ParameterizedType) aClass.getGenericSuperclass();
// Get the generic reflection class
Type[] actualTypeArguments = genericSuperclass.getActualTypeArguments();
clazz = (Class<?>) actualTypeArguments[0];
BaseDao It implements a simple CRUD operation
package com.qy151.util;
import com.qy151.annotation.TabelFiled;
import com.qy151.annotation.TabelName;
import com.qy151.annotation.TableId;
import com.qy151.entity.Student;
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;
/**
* @unthor : YSH
* @date : 20:27 2022/7/14
*/
/*T: Represents an entity class object */
public class BaseDao<T> {
private Class<?> clazz;
public BaseDao(){
//this The corresponding subclass object Get the current reflection class object
Class<? extends BaseDao> aClass = this.getClass();
// Get the parent class of the current reflection class -- Generics containing parent classes
ParameterizedType genericSuperclass = (ParameterizedType) aClass.getGenericSuperclass();
// Get the generic reflection class
Type[] actualTypeArguments = genericSuperclass.getActualTypeArguments();
clazz= (Class<?>) actualTypeArguments[0];
/*System.out.println(clazz);*/
}
/* Query single and query all public methods */
public List<T> find(String sql) throws Exception{
List<T> list = new ArrayList<T>();
Connection connection = DBUtils.getCon();
PreparedStatement ps = connection.prepareStatement(sql.toString());
ResultSet rs = ps.executeQuery();
while (rs.next()){
Object o = clazz.newInstance();
Field[] declaredFields = clazz.getDeclaredFields();
for (Field declaredField:declaredFields
) {
declaredField.setAccessible(true);
TabelFiled tabelFiled = declaredField.getAnnotation(TabelFiled.class);
if (tabelFiled==null){
TableId tableId = declaredField.getAnnotation(TableId.class);
if(tableId!=null){
declaredField.set(o,rs.getObject(tableId.value()));
}else {
declaredField.set(o,rs.getObject(declaredField.getName()));
}
}else {
declaredField.set(o, rs.getObject(tabelFiled.value()));
}
}
list.add((T) o);
}
return list;
}
/* according to id Inquire about */
public Student findOneById(Object id) throws Exception {
Student student = null;
StringBuffer sql = new StringBuffer("select * from ");
// Get table name
TabelName tabelNameAnnotation = clazz.getAnnotation(TabelName.class);
String tabelname = "";
/* Determine whether the annotation exists */
if (tabelNameAnnotation != null) {
tabelname = tabelNameAnnotation.value();
} else {
tabelname = clazz.getSimpleName();
}
// Append table name
sql.append(tabelname+" where ");
System.out.println(sql);
// Get all attribute objects in the reflection class object
Field[] declaredFields = clazz.getDeclaredFields();
boolean flag = false;
for (Field declaredFiled:declaredFields
) {
TableId tableId = declaredFiled.getAnnotation(TableId.class);
if (tableId!=null){
sql.append(tableId.value()+"='"+id+"'");
flag=true;
break;
}
}
if (flag==false){
throw new RuntimeException(" No primary key annotation is added ");
}
System.out.println(sql);
List<T> list = find(sql.toString());
if (list!=null&&list.size()==1){
return (Student) list.get(0);
}
return null;
}
// Query all
public List<T> findAll() throws Exception{
StringBuffer sql = new StringBuffer("select * from ");
// Get table name
TabelName tabelNameAnnotation = clazz.getAnnotation(TabelName.class);
String tabelname = "";
/* Determine whether the annotation exists */
if (tabelNameAnnotation != null) {
tabelname = tabelNameAnnotation.value();
} else {
tabelname = clazz.getSimpleName();
}
// Append table name
sql.append(tabelname);
System.out.println(sql);
return find(sql.toString());
}
// Delete
public int delete(Object id){
try {
StringBuffer sql = new StringBuffer("delete from ");
// Get table name
TabelName tabelNameAnnotation = clazz.getAnnotation(TabelName.class);
String tabelname = "";
/* Determine whether the annotation exists */
if (tabelNameAnnotation != null) {
tabelname = tabelNameAnnotation.value();
} else {
tabelname = clazz.getSimpleName();
}
// Append table name
sql.append(tabelname+" where ");
System.out.println(sql);
// Get all attribute objects in the reflection class object
Field[] declaredFields = clazz.getDeclaredFields();
boolean flag = false;
for (Field declaredFiled:declaredFields
) {
TableId tableId = declaredFiled.getAnnotation(TableId.class);
if (tableId!=null){
sql.append(tableId.value()+"='"+id+"'");
flag=true;
break;
}
}
if (flag==false){
throw new RuntimeException(" No primary key annotation is added ");
}
System.out.println(sql);
// Get the connection object
Connection con = DBUtils.getCon();
// obtain sql Statement object
PreparedStatement ps = con.prepareStatement(sql.toString());
// perform sql sentence
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}
return 0;
}
// increase
public int insert(T t) {
try {
//Sql:insert into Table name values(?,?,?......)
StringBuffer stringBuffer = new StringBuffer("insert into ");
// Get table name
Class<?> aClass = t.getClass();
TabelName tabelNameAnnotation = aClass.getAnnotation(TabelName.class);
String tabelname = "";
/* Determine whether the annotation exists */
if (tabelNameAnnotation != null) {
tabelname = tabelNameAnnotation.value();
} else {
tabelname = aClass.getSimpleName();
}
// Append table name
stringBuffer.append(tabelname);
// Get all attribute objects in the reflection class object
Field[] declaredFields = aClass.getDeclaredFields();
// Create two sets
List<String> columns = new ArrayList<String>();// Store all column names
List<String> values = new ArrayList<String>();// Store all column values
for (Field field : declaredFields
) {
field.setAccessible(true);
// Get all column names
TabelFiled tabelFiled = field.getAnnotation(TabelFiled.class);
if (tabelFiled != null) {
columns.add(tabelFiled.value());
} else {
columns.add(field.getName());
}
// Get all column values
values.add("'" + field.get(t) + "'");
}
stringBuffer.append(columns.toString().replace("[", "(").replace("]", ")"));
stringBuffer.append(" values ");
stringBuffer.append(values.toString().replace("[", "(").replace("]", ")"));
System.out.println(stringBuffer);
// Get the connection object
Connection con = DBUtils.getCon();
// obtain sql Statement object
PreparedStatement ps = con.prepareStatement(stringBuffer.toString());
// perform sql sentence
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}finally {
}
return 0;
}
/* modify 01*/
public int update(T t){
try {
//update Table name set Name = ? where id=?
StringBuffer stringBuffer = new StringBuffer("update ");
/* Get the reflection object */
Class<?> aClass = t.getClass();
TabelName tabelNameAnnotation = aClass.getAnnotation(TabelName.class);
String tablename = "";
if (tabelNameAnnotation != null) {
tablename = tabelNameAnnotation.value();
} else {
tablename = aClass.getSimpleName();
}
stringBuffer.append(tablename + " set ");
Field[] declaredFields = aClass.getDeclaredFields();
List<String> columns = new ArrayList<String>();
List<String> values = new ArrayList<String>();
for (Field field : declaredFields
) {
field.setAccessible(true);
TabelFiled tabelFiled = field.getAnnotation(TabelFiled.class);
if (tabelFiled != null) {
columns.add(tabelFiled.value());
} else {
columns.add(field.getName());
}
values.add("'" + field.get(t) + "'");
}
String remove = columns.remove(0);
String remove01 = values.remove(0);
System.out.println(remove + " " + remove01);
Object[] columnsArray = columns.toArray();
Object[] valuesArray = values.toArray();
for (int i = 0; i < columnsArray.length; i++) {
for (int j = 0; j < valuesArray.length; j++) {
if (i == j) {
stringBuffer.append(columnsArray[i] + "=" + valuesArray[j] + ",");
}
}
}
stringBuffer = new StringBuffer(stringBuffer.substring(0, stringBuffer.length() - 1) + " where " + remove + "=" + remove01);
System.out.println(stringBuffer);
Connection con = DBUtils.getCon();
PreparedStatement ps= con.prepareStatement(stringBuffer.toString());
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}finally {
}
return 0;
}
/* modify 02*/
public int updateById(T t){
try {
// modify --update Table name set Name = value , Name = value ... where Primary key = value ;
StringBuffer sql = new StringBuffer("update ");
/* Get table name */
Class<?> aClass = t.getClass();
TabelName tabelNameAnnotation = aClass.getAnnotation(TabelName.class);
String tableName = "";
if (tabelNameAnnotation != null) {
tableName = tabelNameAnnotation.value();
} else {
tableName = aClass.getSimpleName();
}
sql.append(tableName + " set ");
System.out.println(sql);
/* Get column values */
String columnValue = "";
String where = " where ";
Field[] declaredFields = aClass.getDeclaredFields();
boolean flag = false;
for (Field field : declaredFields
) {
field.setAccessible(true);
TabelFiled tabelFiledAnnotation = field.getAnnotation(TabelFiled.class);
if (tabelFiledAnnotation != null) {
columnValue += tabelFiledAnnotation.value() + "='" + field.get(t) + "', ";
} else {
TableId tableIdAnnotation = field.getAnnotation(TableId.class);
if (tableIdAnnotation!=null){
flag = true;
where +=tableIdAnnotation.value()+"='"+field.get(t)+"'";
}else {
columnValue+= field.getName()+ "='" + field.get(t) + "',";
}
}
}
if (flag==false){
throw new RuntimeException(" No primary key annotation is added ");
}
// Remove the last question mark
columnValue=columnValue.substring(0,columnValue.lastIndexOf(","));
sql.append(columnValue).append(where);
System.out.println(sql );
Connection con = DBUtils.getCon();
PreparedStatement ps= con.prepareStatement(sql.toString());
int i = ps.executeUpdate();
return i;
}catch (Exception e){
e.printStackTrace();
}
return 0;
}
}
entity package : Entity class Student
package com.qy151.entity;
import com.qy151.annotation.TabelFiled;
import com.qy151.annotation.TabelName;
import com.qy151.annotation.TableId;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
/**
* @unthor : YSH
* @date : 20:34 2022/7/14
*/
@Data
/*@NoArgsConstructor
@AllArgsConstructor*/
@TabelName(value = "t_student")
public class Student {
/*private Integer id;*/
@TabelFiled(value = "name")
private String studentname;
private String address;
// Indicates that the column is a primary key column
@TableId(value = "id")
private Integer sid;
}
dao package : Operation class
package com.qy151.dao;
import com.qy151.entity.Student;
import com.qy151.util.BaseDao;
/**
* @unthor : YSH
* @date : 20:49 2022/7/14
*/
public class StudentDao extends BaseDao<Student> {
}
Test: Test class
import com.qy151.dao.StudentDao;
import com.qy151.dao.UserDao;
import com.qy151.entity.Student;
import com.qy151.entity.User;
import org.junit.Test;
/**
* @unthor : YSH
* @date : 20:49 2022/7/14
*/
public class StudentTest {
StudentDao studentDao = new StudentDao();
@Test
public void insert(){
Student student = new Student();
student.setSid(20);
student.setStudentname(" Saturday ");
student.setAddress(" Beijing ");
studentDao.insert(student);
}
@Test
public void update() {
Student student = new Student();
student.setSid(20);
student.setStudentname(" Zhang San ");
student.setAddress(" Venus ");
studentDao.update(student);
}
@Test
public void updateById() {
Student student = new Student();
student.setSid(20);
student.setStudentname(" Zhang San ");
student.setAddress(" mercury ");
studentDao.updateById(student);
}
@Test
public void delete(){
Student student = new Student();
studentDao.delete(20);
}
@Test
public void findAll() throws Exception {
Student student = new Student();
System.out.println(studentDao.findAll());
}
@Test
public void findOneById() throws Exception {
Student student = new Student();
System.out.println(studentDao.findOneById(10));
}
}
IDEA Package the project as jar package
https://blog.csdn.net/weixin_61634823/article/details/124827963Include dependencies used in the project
packaged jar In bag Lombok The package cannot be used , Report errors
resolvent :
Turn on idea Annotation Processing
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