java annotation简单模拟hibernate

昨天看了看注解,于是简单模拟一下hibernate

整个包:

先来看注解Table.java,主要是把实体类和表名联系起来

package annotation;

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

//自定义的Annotation
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
    String name() default "";
}

然后是实体类Model.java,用刚写好的注解@Table配置一下

package annotation;

//实体类
@Table(name = "_model")    //用annotation配置
public class Model {
    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

SessionFactory主要是读取注解配置(通过反射很easy),然后把实体类放入容器中

package annotation;

import java.io.File;
import java.util.HashMap;
import java.util.Map;

//annotation配置文件的解读
public class SessionFactory {
    private Map<Class, String> tableMap = new HashMap<Class, String>();

    private static SessionFactory sf = new SessionFactory();

    private SessionFactory() {
    }

    public static SessionFactory config() throws Exception {
        // 读取包名为annotation下所有class
        File f = new File(System.getProperty("user.dir") + "/bin/annotation");
        File[] files = f.listFiles();
        for (int i = 0; i < files.length; i++) {
            String fileName = files[i].getName();
            // 载入class
            Class clazz = Class.forName("annotation."
                    + fileName.substring(0, fileName.indexOf(".")));
            // 检查该类是否加有Table注解
            Table t = (Table) clazz.getAnnotation(Table.class);
            // 加入Table注解的放入容器中
            if (t != null) {
                sf.getTableMap().put(clazz, t.name());
            }
        }
        return sf;
    }

    public Session openSession() {
        return new Session(tableMap);
    }

    public Map<Class, String> getTableMap() {
        return tableMap;
    }

    public void setTableMap(Map<Class, String> tableMap) {
        this.tableMap = tableMap;
    }

}

session类主要负责数据库连接和sql语句处理

package annotation;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.HashMap;
import java.util.Map;

//负责数据库连接,包括生成及执行sql语句
public class Session {

    private Map<Class, String> tableMap = new HashMap<Class, String>();

    public Session(Map<Class, String> tableMap) {
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        this.tableMap = tableMap;
    }

    // 储存
    public void save(Object o) throws Exception {
        Class clazz = o.getClass();
        String tableName = tableMap.get(clazz);
        // 表列名
        String keys = "";
        // 值
        String vals = "";
        Field[] fields = clazz.getDeclaredFields();
        for (Field f : fields) {
            // 构造列名
            keys += f.getName() + ",";
            // 得到get**方法,得到列的对应值
            String ms = "get" + Character.toUpperCase(f.getName().charAt(0))
                    + f.getName().substring(1);
            Method m = clazz.getDeclaredMethod(ms);
            Object obj = m.invoke(o, null);
            if (obj instanceof Integer) {
                vals += obj + ",";
            }
            if (obj instanceof String) {
                vals += "'" + obj + "'" + ",";
            }
        }
        keys = keys.substring(0, keys.length() - 1);
        vals = vals.substring(0, vals.length() - 1);
        String sql = createSaveSQL(tableName, keys, vals);
        executeSQL(sql);
    }

    private void executeSQL(String sql) throws Exception {
        Connection conn = DriverManager.getConnection(
                "jdbc:mysql://localhost/test", "root", "lj123456");
        conn.createStatement().execute(sql);
        conn.close();
    }

    // 建sql语句
    private String createSaveSQL(String tableName, String keys, String vals) {
        String sql = "insert into " + tableName + " (" + keys + ") values ("
                + vals + ")";
        return sql;
    }
}

Main.java 来测试一下代码

package annotation;


public class Main {
    public static void main(String[] args) throws Exception {
        SessionFactory sf = SessionFactory.config();
        Session session = sf.openSession();
        Model m = new Model();
        m.setId(1);
        m.setName("first");
        session.save(m);
    }
}

结果:

O啦,暂时没有模拟hibernate其他注解,但原理一样,就偷偷懒呗.