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.