/**
* loader :类加载器
* interfaces:目标对象实现的接口
* h:InvocationHandler的实现类
*/
public static Object newProxyInstance(ClassLoader loader,
Class[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
final Class[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.从缓存中查找或生成目标对象的代理类
*/
Class cl = getProxyClass0(loader, intfs);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
//调用代理对象的构造函数(代理对象的构造函数$Proxy0(InvocationHandler h),通过字节码反编译可以查看生成的代理类)
final Constructor cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
}
//生成代理类的实例,并把MyInvocationHander的实例作为构造函数参数传入
return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) {
throw new InternalError(e.toString(), e);
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString(), t);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString(), e);
}
}
进到getProxyClass0方法
private static Class getProxyClass0(ClassLoader loader,
Class... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
// If the proxy class defined by the given loader implementing
// the given interfaces exists, this will simply return the cached copy;
// otherwise, it will create the proxy class via the ProxyClassFactory
return proxyClassCache.get(loader, interfaces);
}
public interface BiFunction {
R apply(T t, U u);
}
private static final class ProxyClassFactory
implements BiFunction[], Class>
{
// prefix for all proxy class names 代理类的前缀
private static final String proxyClassNamePrefix = "$Proxy";
// next number to use for generation of unique proxy class names
//生成唯一的代理类名称
private static final AtomicLong nextUniqueNumber = new AtomicLong();
@Override
public Class apply(ClassLoader loader, Class[] interfaces) {
Map, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class intf : interfaces) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
//确保接口的类对象与类加载器加载的类对象相同,且由同一个加载器加载。《深入理解java虚拟机》提到,类加载器虽然只用于实现类的加载动作,但在java程序起的作用远不止于类的加载。对于任何一个类,都需要由加载它的的类加载器和这个类本身一同确立其在java虚拟机中的唯一性,每一个类加载器,都拥有一个独立的类名称空间,通俗点,比较两个类是否相等,只有在这两个类是由同一个类加载器加载的前提下才有意义,否则,即使这两个类来源于同一个class文件,被同一个虚拟机加载,只要加载它们的类加载器不同,那这两个类就必定不相等。interfaceClass = Class.forName(intf.getName(), false, loader);验证类是否相等,实现原理如上所述。
Class interfaceClass = null;
try {
interfaceClass = Class.forName(intf.getName(), false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != intf) {
throw new IllegalArgumentException(
intf + " is not visible from class loader");
}
/*
* Verify that the Class object actually represents an
* interface. 验证类对象表示的是接口
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate. 验证接口未重复
*/
if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
}
String proxyPkg = null; // package to define proxy class in定义待生成的代理类所在包名
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* Record the package of a non-public proxy interface so that the
* proxy class will be defined in the same package. Verify that
* all non-public proxy interfaces are in the same package.非public修饰的代理接口,需要定义在相同的包中,如果非public修饰的接口不在相同包,会因访问权限的限制而无法访问。intf.getModifiers()返回的是一个整数,用不同的位开关表示接口中public/final修饰符的使用情况。
*/
for (Class intf : interfaces) {
int flags = intf.getModifiers();
if (!Modifier.isPublic(flags)) {
accessFlags = Modifier.FINAL;
String name = intf.getName();
int n = name.lastIndexOf('.');
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null) {
proxyPkg = pkg; //代理对象的包名,如com.aop
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}
if (proxyPkg == null) {
// if no non-public proxy interfaces, use com.sun.proxy package
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
}
/*
* Choose a name for the proxy class to generate.
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* Generate the specified proxy class.
*生成目标对象的代理类的字节码,并保存到硬盘中。
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try {
//返回代理类对象,将字节码加载到内存中
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
}
/**
*映射接口数组到最后键的函数
* 接口数组映射到最优键对象上(如实例化Key1时,接口作为Key1的构造函数参数,保存到Key1中), 同时,Key1/Key2/KeyX继承了WeakReference弱引用类类,因此接口所在的类对象被弱引用
*/
private static final class KeyFactory
implements BiFunction[], Object>
{
@Override
public Object apply(ClassLoader classLoader, Class[] interfaces) {
switch (interfaces.length) {
case 1: return new Key1(interfaces[0]); // the most frequent
case 2: return new Key2(interfaces[0], interfaces[1]);
case 0: return key0;
default: return new KeyX(interfaces);
}
}
}
public V get(K key, P parameter) {
Objects.requireNonNull(parameter);
expungeStaleEntries();
//refQueue的类型为ReferenceQueue,存放对象的弱引用,CacheKey继承了WeakReference,因此key(ClassLoader)所在对象被弱引用,对象的应用存放在队列refQueue中。
Object cacheKey = CacheKey.valueOf(key, refQueue);
// lazily install the 2nd level valuesMap for the particular cacheKey
//生成第一层key,从缓存中获取valuesMap,如果为空,则新建ConcurrentHashMap实例,把当前加载器和ConcurrentHashMap实例放到缓存中。
ConcurrentMap
V value = supplier.get(); value为缓存中的代理类对象,Supplier是个接口,实现代码是在接口的实现类Factory中, 进入WeakCache类的内部类Factory,查看get方法。如下:
Supplier是接口
public interface Supplier {
/**
* Gets a result.
*
* @return a result
*/
T get();
}
}
Factory是WeakCache的内部类, Factory实现了接口Supplier
private final class Factory implements Supplier {
private final K key;
private final P parameter;
private final Object subKey;
private final ConcurrentMap> valuesMap;
Factory(K key, P parameter, Object subKey,
ConcurrentMap> valuesMap) {
this.key = key;
this.parameter = parameter;
this.subKey = subKey;
this.valuesMap = valuesMap;
}
@Override
public synchronized V get() { // serialize access
// re-check
Supplier supplier = valuesMap.get(subKey);
if (supplier != this) {
// something changed while we were waiting:
// might be that we were replaced by a CacheValue
// or were removed because of failure ->
// return null to signal WeakCache.get() to retry
// the loop
return null;
}
// else still us (supplier == this)
// create new value
V value = null;
try {
//valueFactory.apply(key, parameter) 返回代理类对象,即Class对象。
//如果value不为空,说明缓存中已经存在代理类,可以直接返回。
//通过前面的判断,已经能确定缓存中存在代理类,否则,程序是走不到这里来的。
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
} finally {
if (value == null) { // remove us on failure
valuesMap.remove(subKey, this);
}
}
// the only path to reach here is with non-null value
assert value != null;
// wrap value with CacheValue (WeakReference)
CacheValue cacheValue = new CacheValue<>(value);
// try replacing us with CacheValue (this should always succeed)
if (valuesMap.replace(subKey, this, cacheValue)) {
// put also in reverseMap
reverseMap.put(cacheValue, Boolean.TRUE);
} else {
throw new AssertionError("Should not reach here");
}
// successfully replaced us with new CacheValue -> return the value
// wrapped by it
return value;
}
}
动态代理代理模式的解释:为其他对象提供一种代理以控制对这个对象的访问,增强一个类中的某个方法,对程序进行扩展。比如,现在存在一个UserService类:public class UserService { public void test() { System.out.println("test..."); }}此时,我们new一个UserService对象,然后执行test()方法,结果是
spring JMS对于异步消息处理基本上只需配置下就能进行高效的处理。其核心就是消息侦听器容器,常用的类就是DefaultMessageListenerContainer。该容器可配置侦听器的并发数量,以及配合MessageListenerAdapter使用消息驱动POJO进行消息处理。且消息驱动POJO是放入TaskExecutor中进行处理,进一步提高性能,减少侦听器的阻塞。具体配置如下:
ZIP文件的解压缩实质上就是从输入流中读取数据。Java.util.zip包提供了类ZipInputStream来读取ZIP文件,下面的代码段创建了一个输入流来读取ZIP格式的文件;
ZipInputStream in = new ZipInputStream(new FileInputStream(zipFileName));
&n
Spring可以通过注解@Transactional来为业务逻辑层的方法(调用DAO完成持久化动作)添加事务能力,如下是@Transactional注解的定义:
/*
* Copyright 2002-2010 the original author or authors.
*
* Licensed under the Apache License, Version
使用nginx lua已经两三个月了,项目接开发完毕了,这几天准备上线并且跟高德地图对接。回顾下来lua在项目中占得必中还是比较大的,跟PHP的占比差不多持平了,因此在开发中遇到一些问题备忘一下 1:content_by_lua中代码容量有限制,一般不要写太多代码,正常编写代码一般在100行左右(具体容量没有细心测哈哈,在4kb左右),如果超出了则重启nginx的时候会报 too long pa
import java.util.Stack;
public class ReverseStackRecursive {
/**
* Q 66.颠倒栈。
* 题目:用递归颠倒一个栈。例如输入栈{1,2,3,4,5},1在栈顶。
* 颠倒之后的栈为{5,4,3,2,1},5处在栈顶。
*1. Pop the top element
*2. Revers
仅作笔记使用
public class VectorQueue {
private final Vector<VectorItem> queue;
private class VectorItem {
private final Object item;
private final int quantity;
public VectorI