学习hibernate的源代码-------对象属性延迟加载
自己参考hibernate的源代码，写了个大概能演示hibernate对对象熟悉延迟加载的几个类，用到了javassist 包。
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??调用的接口是这样的：
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public class Test {public static void main(String[] args) {HibernateSeesion session = new HibernateSeesion();Custerinform c1 = (Custerinform)session.load(Custerinform.class, "2");//延迟加载对象上除了id以外的熟悉,无需连接数据库System.out.println(c1.getId());//正在需要用到其他熟悉时，再去数据库加载数据System.out.println(c1.getFirstName());//复用已经完全加载出来的对象，无需再连接数据库System.out.println(c1.getLastName());}}??
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import java.io.Serializable;import java.util.HashMap;import java.util.Map;public class HibernateSeesion {private static Map<String,Object> memDataBase = new HashMap<String,Object>();//mock database//一个标识接口，为每个被代理的对象都加上这个接口private static Class<?>[] proxyInterfaces = {HibernateProxy.class};//proxy工厂private static Class<?> proxyFactory;static{Custerinform cust1 = new Custerinform();cust1.setId("1");cust1.setFirstName("张");cust1.setLastName("阳");Custerinform cust2 = new Custerinform();cust2.setId("2");cust2.setFirstName("张");cust2.setLastName("梓琳");memDataBase.put(Custerinform.class.getName() + cust1.getId(), cust1);memDataBase.put(Custerinform.class.getName() + cust2.getId(), cust2);//这里的写法，只是为了简单模拟一下hibernate的机制而已proxyFactory = LazyInitializer.getProxyFactory(Custerinform.class,proxyInterfaces);}/** * 返回proxy对象 * @param theClass * @param id * @return */public Object load(Class<?> theClass, Serializable id){return LazyInitializer.getProxy(proxyFactory, this, Custerinform.class.getName(),id);}/** * 模拟从数据库中即使加载 * @param entityName * @param id * @return */public Object immediateLoad(String entityName, Serializable id){return memDataBase.get(entityName+id);}}??
?? 下面这个类是整个延迟加载的核心类容，
?? ?proxyfatory 和 proxy 都是在这里生成的，借助了 ?javassist 包提供的api。
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import java.io.Serializable;import java.lang.reflect.Method;import javassist.util.proxy.MethodHandler;import javassist.util.proxy.ProxyFactory;import javassist.util.proxy.ProxyObject;public class LazyInitializer implements MethodHandler {private static final String INVOKE = "INVOKE";private boolean constructed = false;private boolean initialized = false;private Serializable id;private Object target;private HibernateSeesion session;private String entityName;public LazyInitializer(final HibernateSeesion session, final String entityName, final Serializable id) {this.id = id;this.session = session;this.entityName = entityName;}public static Class<?> getProxyFactory(final Class<?> persistentClass, Class<?>[] interfaces) {try {ProxyFactory factory = new ProxyFactory();factory.setSuperclass(persistentClass);factory.setInterfaces(interfaces);return factory.createClass();} catch (Throwable t) {throw new RuntimeException("Javassist Enhancement failed: " + persistentClass.getName(), t);}}public static HibernateProxy getProxy(final Class<?> factory, final HibernateSeesion session,final String entityName, final Serializable id) {final LazyInitializer instance = new LazyInitializer(session, entityName, id);HibernateProxy proxy;try {proxy = (HibernateProxy) factory.newInstance();} catch (Exception e) {throw new RuntimeException("Javassist Enhancement failed: " + entityName, e);}((ProxyObject) proxy).setHandler(instance);instance.constructed = true;return proxy;}@Overridepublic Object invoke(Object proxy, Method thisMethod, Method proceed, Object[] args) throws Throwable {if (this.constructed) {Object result;final Object returnValue;result = this.invoke(thisMethod, args, proxy); //判断被调用的方法是不是getIdif (result == INVOKE) {Object target = getInvoke(); //获取目标对象returnValue = thisMethod.invoke(target, args); //在目标对象上调用方法return returnValue == target ? proxy : returnValue;} else {return result;}} else {return proceed.invoke(proxy, args);}}public final Serializable getIdentifier() {return id;}public final void setIdentifier(Serializable id) {this.id = id;}public final Object getInvoke() {initialize();return target;}/** * 拦截 getId 方法，如果只是请求这个方法的话，无需从数据库中加载数据 */private final Object invoke(Method method, Object[] args, Object proxy) {String methodName = method.getName();int params = args.length;if (params == 0) {if (methodName.equals("getId")) {return getIdentifier();}}return INVOKE;}/** * 初始化代理对象的目标对象 */private final void initialize() {if (!initialized) {System.out.println("load data from database");target = session.immediateLoad(entityName, id);initialized = true;} else {checkTargetState();}}private void checkTargetState() {if (target == null) {System.out.println("找不到数据");}}}??
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public interface HibernateProxy {}??
public class Custerinform {private String id;private String firstName;private String lastName;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getFirstName() {return firstName;}public String getLastName() {return lastName;}public void setFirstName(String firstName) {this.firstName = firstName;}public void setLastName(String lastName) {this.lastName = lastName;}}