【转】java 利用注解、反射模拟ORM实现

/**
 * org.crazystone.annotation
 *
 * Function： TODO
 *
 *   ver     date           author
 * ──────────────────────────────────
 *           2012-9-11      zhangzenglun
 *
 * Copyright (c) 2012, TNT All Rights Reserved.
 */

package org.crazystone.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 *
 * @author zhangzenglun
 * @version 1.0
 * @since v1.0
 * @Date 2012-9-11 下午2:06:08
 */

/**
 * @Retention用来声明注解的保留策略，有CLASS、RUNTIME和SOURCE这三种，分别表示注解保存在类文件、JVM运行时刻和源代码中。
 * 只有当声明为RUNTIME的时候，才能够在运行时刻通过反射API来获取到注解的信息。
 *
 * @Target用来声明注解可以被添加在哪些类型的元素上，如类型、方法和域等
 */

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Table {
    String tableName();
}

/**
 * TableField.java
 * org.crazystone.annotation
 *
 * Function： TODO
 *
 *   ver     date           author
 * ──────────────────────────────────
 *           2012-9-11      zhangzenglun
 *
 * Copyright (c) 2012, TNT All Rights Reserved.
 */

package org.crazystone.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * ClassName:TableField
 *
 * @author zhangzenglun
 * @version 1.0
 * @since v1.0
 * @Date 2012-9-11 下午2:14:41
 */

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD,ElementType.METHOD})
public @interface TableField {
    public String name();

    public boolean isPrimaryKey() default false;
}

/**
 * User.java
 * org.crazystone.annotation
 *
 * Function： TODO
 *
 *   ver     date           author
 * ──────────────────────────────────
 *           2012-9-11      zhangzenglun
 *
 * Copyright (c) 2012, TNT All Rights Reserved.
 */

package org.crazystone.annotation;

/**
 * ClassName:User
 *
 * @author zhangzenglun
 * @version 1.0
 * @since v1.0
 * @Date 2012-9-11 下午2:01:06
 */

@Table(tableName = "user")
public class User {
    @TableField(name = "user_id", isPrimaryKey = true)
    private int userId;
    @TableField(name = "user_name")
    private String userName;
    @TableField(name = "user_age")
    private int age;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

}

/**
 * BaseOrmSupport.java
 * org.crazystone.annotation
 *
 * Function： TODO
 *
 *   ver     date           author
 * ──────────────────────────────────
 *           2012-9-11      zhangzenglun
 *
 * Copyright (c) 2012, TNT All Rights Reserved.
*/

package org.crazystone.annotation;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * ClassName:BaseOrmSupport
 *
 * @author   zhangzenglun
 * @version  1.0
 * @since    v1.0
 * @Date     2012-9-11 下午3:27:00
 */
public abstract  class BaseOrmSupport<T> {
    public  void save(T o){
        Class<? extends Object> entityClass = o.getClass();
        StringBuffer sql = new StringBuffer();

        sql.append("insert into ");

        Table a = (Table)entityClass.getAnnotation(Table.class);
        if (a!=null) {
            sql.append(a.tableName());
        } else {
            sql.append(entityClass.getName().substring(entityClass.getName().lastIndexOf(".")+1));
        }

        sql.append(" (");

        Field[] fields = entityClass.getDeclaredFields();
        String temp = "";
        StringBuffer valueSql = new StringBuffer();
        for (Field f:fields) {
            TableField tf = f.getAnnotation(TableField.class);

            //获得字段第一个字母大写
            String firstLetter = f.getName().substring(0,1).toUpperCase();
            //转换成字段的get方法
            String getMethodName = "get"+firstLetter+f.getName().substring(1);
            try {

                Method getMethod = entityClass.getMethod(getMethodName, new Class[] {});
                //这个对象字段get方法的值
                Object value = getMethod.invoke(o, new Object[] {});

                if (f.getType().getName().equals(java.lang.String.class.getName())) {
                    valueSql.append(temp+"'"+value+"'");
                } else {
                    valueSql.append(temp+value);
                }

            } catch (Exception e) {
            }

            if (tf != null) {
                sql.append(temp+tf.name());
            } else {
                sql.append(temp+f.getName());
            }
            temp = ",";
        }

        sql.append(")values(");
        sql.append(valueSql);
        sql.append(")");

        System.out.println(sql.toString());
    }
}

/**
 * User.java
 * org.crazystone.annotation
 *
 * Function： TODO
 *
 *   ver     date           author
 * ──────────────────────────────────
 *           2012-9-11      zhangzenglun
 *
 * Copyright (c) 2012, TNT All Rights Reserved.
 */

package org.crazystone.annotation;

/**
 * ClassName:User
 *
 * @author zhangzenglun
 * @version 1.0
 * @since v1.0
 * @Date 2012-9-11 下午2:01:06
 */

public class UserDAO extends BaseOrmSupport<User>{

}

测试类 

package org.crazystone.annotation;

import junit.framework.TestCase;

public class AppTest
    extends TestCase
{

    public void testApp()
    {
        User user = new User();
        user.setAge(100);
        user.setUserName("skylun");
        user.setUserId(1);

        UserDAO userDao = new UserDAO();
        userDao.save(user);
    }

}

测试输出结果： 
insert into user (user_id,user_name,user_age)values(1,'skylun',100)

 

原文有附件。

转自：http://lunzi.iteye.com/blog/1675871