纯手写ORM框架

必须掌握Java的反射机制和自定义注解

package com.wyh.test;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;

//注解是对应表的关联
@Retention(RetentionPolicy.RUNTIME)
@interface Table {
String value();
}

//属性对应注解
@Retention(RetentionPolicy.RUNTIME)
@interface Propety {
String name();

int leng() default 0;

}
@Table("student")
class Student 
{
@Propety(name = "student_id", leng = 10)
private String studentId;
@Propety(name = "student_name")
private String studentName;
@Propety(name = "student_age")
private String studentAge;
public String getStudentId() {

return studentId;
}
public void setStudentId(String studentId) {

this.studentId = studentId;
}
public String getStudentName() {

return studentName;
}
public void setStudentName(String studentName) {

this.studentName = studentName;
}
public String getStudentAge() {

return studentAge;
}
public void setStudentAge(String studentAge) {

this.studentAge = studentAge;
}


}
public class Test003 {
public static void main(String[] args) throws ClassNotFoundException {
Class<?> forName = Class.forName("com.wyh.test.Student");//反射机制

// 获取所有当前的方法
Field[] declaredFields = forName.getDeclaredFields();
StringBuffer sf = new StringBuffer();
sf.append(" select ");
for (int i = 0; i < declaredFields.length; i++) {
Field field = declaredFields[i];
//获取属性上的注解
Propety propety = field.getDeclaredAnnotation(Propety.class);
sf.append(propety.name());
if (i < declaredFields.length - 1) {
sf.append(" , ");
}
}
// 获取类上注解参数
Table declaredAnnotation = forName.getDeclaredAnnotation(Table.class);
sf.append(" from " + declaredAnnotation.value());
System.out.println(sf.toString());
}
}