java lib应该放哪个文件夹 java的lib

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技术领航博主 2023-09-28 00:50:50

文章标签 java lib应该放哪个文件夹 java 开发语言代理类字节码 文章分类 Java 后端开发

CGLib (Code Generation Library) 是一个强大的、高性能、高质量的 Code 生成类库。它可以在运行期扩展 Java 类与实现 Java 接口。Hibernate 用它来实现 PO 字节码的动态生成。CGLib 比 Java 的 java.lang.reflect.Proxy 类更强的在于它不仅可以接管接口类的方法，还可以接管普通类的方法。
CGLib 的底层是 Java 字节码操作框架 —— ASM。

Cglib动态代理的简单示例

1、引入Cglib的maven依赖：

<dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>3.3.0</version>
        </dependency>

2、定义一个目标类，也就是被代理类，此时是一个图书管理员类，管理一些Book类对象（Book类为简单实体类，此处不贴代码）。

package org.example.proxy.cglib;

import org.example.domain.Book;

import java.util.HashMap;
import java.util.Map;

public class Librarian {

    private Map<String, Book> books = new HashMap<>();

    public void addBook(Book book) {
        String name = book.getBookName();
        if (!books.containsKey(name)) {
            books.put(name, book);
        }
    }

    public Book getBook(String name) {
        System.out.println("这里是 " + this.getClass().getName() + " 的getBook方法");
        return books.getOrDefault(name, null);
    }
}

3、定义一个代理工厂类，用来创建代理对象：

package org.example.proxy.cglib;

import net.sf.cglib.core.DebuggingClassWriter;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import org.example.domain.Book;

import java.lang.reflect.Method;

public class CglibProxyFactory {

    public Object getProxy(Object targetObject) {

        Enhancer enhancer = new Enhancer();
        
		//Cglib代理基于创建子类重写父类方法实现，所以这里要确定父类，也就是被代理类。
        Class<?> superClass = targetObject.getClass();
        enhancer.setSuperclass(superClass);

        /*
        创建了一个MethodInterceptor拦截器接口的实现类对象，重写intercept回调方法，
        参数依次为：代理对象、代理方法、方法参数、方法代理
        */
        MethodInterceptor interceptor = new MethodInterceptor() {
            @Override
            public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
                System.out.println("这是前置增强");
                Object res = methodProxy.invokeSuper(o, objects);
                System.out.println("这是后置增强");
                return res;
            }
        };

        enhancer.setCallback(interceptor);

        return enhancer.create();
    }

    public static void main(String[] args) {
	
		//这里设置一个系统属性，保存Cglib动态代理类的字节码文件
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "target/classes");

		//创建原始对象
        Librarian librarian = new Librarian("LiLei", 18);
        Book book = new Book();
        book.setBookName("钢铁是怎样炼成的");
        librarian.addBook(book);
        librarian.getBook("111");

		//创建代理对象
        CglibProxyFactory cglibProxyFactory = new CglibProxyFactory();
        Librarian librarianProxy = (Librarian) cglibProxyFactory.getProxy(librarian);
        librarianProxy.getBook("111");
    }
}

运行结果如下：

java lib应该放哪个文件夹 java的lib_java

原理

沿着enhancer.create()方法一直往下debug，会走到Enhancer类的generate(ClassLoaderData data)方法中，该方法返回的是代理类的Class
对象。

protected Object create(Object key) {
        try {
            ClassLoader loader = getClassLoader();
            Map<ClassLoader, ClassLoaderData> cache = CACHE;
            ClassLoaderData data = cache.get(loader);
            if (data == null) {
                synchronized (AbstractClassGenerator.class) {
                    cache = CACHE;
                    data = cache.get(loader);
                    if (data == null) {
                        Map<ClassLoader, ClassLoaderData> newCache = new WeakHashMap<ClassLoader, ClassLoaderData>(cache);
                        data = new ClassLoaderData(loader);
                        newCache.put(loader, data);
                        CACHE = newCache;
                    }
                }
            }
            this.key = key;
            //这里拿到一个Enhancer$EnhancerFactoryData对象，包括代理类Class对象、构造器等信息。
            Object obj = data.get(this, getUseCache());
            if (obj instanceof Class) {
                return firstInstance((Class) obj);
            }
            //使用拿到的Enhancer$EnhancerFactoryData对象，实例化代理类对象。
            return nextInstance(obj);
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        }
    }

1）沿着data.get(this, getUseCache())方法往下走，一直到Enhancer父类的generate(ClassLoaderData data)方法中，就是该方法生成了代理类的Class
对象。

protected Class generate(ClassLoaderData data) {
        Class gen;
        Object save = CURRENT.get();
        CURRENT.set(this);
        try {
            ClassLoader classLoader = data.getClassLoader();
            if (classLoader == null) {
                throw new IllegalStateException("ClassLoader is null while trying to define class " +
                        getClassName() + ". It seems that the loader has been expired from a weak reference somehow. " +
                        "Please file an issue at cglib's issue tracker.");
            }
            synchronized (classLoader) {
              String name = generateClassName(data.getUniqueNamePredicate());              
              data.reserveName(name);
              this.setClassName(name);
            }
            if (attemptLoad) {
                try {
                    gen = classLoader.loadClass(getClassName());
                    return gen;
                } catch (ClassNotFoundException e) {
                    // ignore
                }
            }
            //结合当前Enhancer及父类信息生成代理类字节码
            byte[] b = strategy.generate(this);
            String className = ClassNameReader.getClassName(new ClassReader(b));
            ProtectionDomain protectionDomain = getProtectionDomain();
            synchronized (classLoader) { // just in case
                if (protectionDomain == null) {
                    gen = ReflectUtils.defineClass(className, b, classLoader);
                } else {
                	/*
                	内部调用了ClassLoader类的defineClass方法，将字节码转化成类的Class实例，然后调用Class.forName（初始化参数设置为
                	true）强制初始化。
                	*/
                    gen = ReflectUtils.defineClass(className, b, classLoader, protectionDomain);
                }
            }
            //返回代理类Class对象
            return gen;
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        } finally {
            CURRENT.set(save);
        }
    }

包装后得到的Enhancer$EnhancerFactoryData对象结构：

java lib应该放哪个文件夹 java的lib_开发语言_02

2）再看nextInstance(obj)方法，这里最终使用构造器的newInstance方法实例化了代理对象。

public Object newInstance(Class[] argumentTypes, Object[] arguments, Callback[] callbacks) {
            setThreadCallbacks(callbacks);
            try {
                // Explicit reference equality is added here just in case Arrays.equals does not have one
                if (primaryConstructorArgTypes == argumentTypes ||
                        Arrays.equals(primaryConstructorArgTypes, argumentTypes)) {
                    // If we have relevant Constructor instance at hand, just call it
                    // This skips "get constructors" machinery
                    //使用构造器的newInstance方法实例化代理对象。
                    return ReflectUtils.newInstance(primaryConstructor, arguments);
                }
                // Take a slow path if observing unexpected argument types
                return ReflectUtils.newInstance(generatedClass, argumentTypes, arguments);
            } finally {
                // clear thread callbacks to allow them to be gc'd
                setThreadCallbacks(null);
            }

        }

最后看看代理类的字节码文件：

java lib应该放哪个文件夹 java的lib_java_03

Librarian $java lib应该放哪个文件夹 java的lib_java_04$ e9192983字节码反编译后的代码如下：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package org.example.proxy.cglib;

import java.lang.reflect.Method;
import net.sf.cglib.core.ReflectUtils;
import net.sf.cglib.core.Signature;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import org.example.domain.Book;

public class Librarian$$EnhancerByCGLIB$$e9192983 extends Librarian implements Factory {
    private boolean CGLIB$BOUND;
    public static Object CGLIB$FACTORY_DATA;
    private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
    private static final Callback[] CGLIB$STATIC_CALLBACKS;
    private MethodInterceptor CGLIB$CALLBACK_0;
    private static Object CGLIB$CALLBACK_FILTER;
    private static final Method CGLIB$addBook$0$Method;
    private static final MethodProxy CGLIB$addBook$0$Proxy;
    private static final Object[] CGLIB$emptyArgs;
    private static final Method CGLIB$getBook$1$Method;
    private static final MethodProxy CGLIB$getBook$1$Proxy;
    private static final Method CGLIB$equals$2$Method;
    private static final MethodProxy CGLIB$equals$2$Proxy;
    private static final Method CGLIB$toString$3$Method;
    private static final MethodProxy CGLIB$toString$3$Proxy;
    private static final Method CGLIB$hashCode$4$Method;
    private static final MethodProxy CGLIB$hashCode$4$Proxy;
    private static final Method CGLIB$clone$5$Method;
    private static final MethodProxy CGLIB$clone$5$Proxy;

    static void CGLIB$STATICHOOK1() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("org.example.proxy.cglib.Librarian$$EnhancerByCGLIB$$e9192983");
        Class var1;
        Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
        CGLIB$equals$2$Method = var10000[0];
        CGLIB$equals$2$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2");
        CGLIB$toString$3$Method = var10000[1];
        CGLIB$toString$3$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$3");
        CGLIB$hashCode$4$Method = var10000[2];
        CGLIB$hashCode$4$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$4");
        CGLIB$clone$5$Method = var10000[3];
        CGLIB$clone$5$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5");
        var10000 = ReflectUtils.findMethods(new String[]{"addBook", "(Lorg/example/domain/Book;)V", "getBook", "(Ljava/lang/String;)Lorg/example/domain/Book;"}, (var1 = Class.forName("org.example.proxy.cglib.Librarian")).getDeclaredMethods());
        CGLIB$addBook$0$Method = var10000[0];
        CGLIB$addBook$0$Proxy = MethodProxy.create(var1, var0, "(Lorg/example/domain/Book;)V", "addBook", "CGLIB$addBook$0");
        CGLIB$getBook$1$Method = var10000[1];
        CGLIB$getBook$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Lorg/example/domain/Book;", "getBook", "CGLIB$getBook$1");
    }

    final void CGLIB$addBook$0(Book var1) {
        super.addBook(var1);
    }

    public final void addBook(Book var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$addBook$0$Method, new Object[]{var1}, CGLIB$addBook$0$Proxy);
        } else {
            super.addBook(var1);
        }
    }

    final Book CGLIB$getBook$1(String var1) {
        return super.getBook(var1);
    }

    public final Book getBook(String var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (Book)var10000.intercept(this, CGLIB$getBook$1$Method, new Object[]{var1}, CGLIB$getBook$1$Proxy) : super.getBook(var1);
    }

    final boolean CGLIB$equals$2(Object var1) {
        return super.equals(var1);
    }

    public final boolean equals(Object var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            Object var2 = var10000.intercept(this, CGLIB$equals$2$Method, new Object[]{var1}, CGLIB$equals$2$Proxy);
            return var2 == null ? false : (Boolean)var2;
        } else {
            return super.equals(var1);
        }
    }

    final String CGLIB$toString$3() {
        return super.toString();
    }

    public final String toString() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$3$Method, CGLIB$emptyArgs, CGLIB$toString$3$Proxy) : super.toString();
    }

    final int CGLIB$hashCode$4() {
        return super.hashCode();
    }

    public final int hashCode() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            Object var1 = var10000.intercept(this, CGLIB$hashCode$4$Method, CGLIB$emptyArgs, CGLIB$hashCode$4$Proxy);
            return var1 == null ? 0 : ((Number)var1).intValue();
        } else {
            return super.hashCode();
        }
    }

    final Object CGLIB$clone$5() throws CloneNotSupportedException {
        return super.clone();
    }

    protected final Object clone() throws CloneNotSupportedException {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? var10000.intercept(this, CGLIB$clone$5$Method, CGLIB$emptyArgs, CGLIB$clone$5$Proxy) : super.clone();
    }

    public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch (var10000.hashCode()) {
            case -1644681230:
                if (var10000.equals("addBook(Lorg/example/domain/Book;)V")) {
                    return CGLIB$addBook$0$Proxy;
                }
                break;
            case -508378822:
                if (var10000.equals("clone()Ljava/lang/Object;")) {
                    return CGLIB$clone$5$Proxy;
                }
                break;
            case 1332997645:
                if (var10000.equals("getBook(Ljava/lang/String;)Lorg/example/domain/Book;")) {
                    return CGLIB$getBook$1$Proxy;
                }
                break;
            case 1826985398:
                if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
                    return CGLIB$equals$2$Proxy;
                }
                break;
            case 1913648695:
                if (var10000.equals("toString()Ljava/lang/String;")) {
                    return CGLIB$toString$3$Proxy;
                }
                break;
            case 1984935277:
                if (var10000.equals("hashCode()I")) {
                    return CGLIB$hashCode$4$Proxy;
                }
        }

        return null;
    }

    public Librarian$$EnhancerByCGLIB$$e9192983() {
        CGLIB$BIND_CALLBACKS(this);
    }

    public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
        CGLIB$THREAD_CALLBACKS.set(var0);
    }

    public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
        CGLIB$STATIC_CALLBACKS = var0;
    }

    private static final void CGLIB$BIND_CALLBACKS(Object var0) {
        Librarian$$EnhancerByCGLIB$$e9192983 var1 = (Librarian$$EnhancerByCGLIB$$e9192983)var0;
        if (!var1.CGLIB$BOUND) {
            var1.CGLIB$BOUND = true;
            Object var10000 = CGLIB$THREAD_CALLBACKS.get();
            if (var10000 == null) {
                var10000 = CGLIB$STATIC_CALLBACKS;
                if (var10000 == null) {
                    return;
                }
            }

            var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
        }

    }

    public Object newInstance(Callback[] var1) {
        CGLIB$SET_THREAD_CALLBACKS(var1);
        Librarian$$EnhancerByCGLIB$$e9192983 var10000 = new Librarian$$EnhancerByCGLIB$$e9192983();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        Librarian$$EnhancerByCGLIB$$e9192983 var10000 = new Librarian$$EnhancerByCGLIB$$e9192983();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        Librarian$$EnhancerByCGLIB$$e9192983 var10000 = new Librarian$$EnhancerByCGLIB$$e9192983;
        switch (var1.length) {
            case 0:
                var10000.<init>();
                CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
                return var10000;
            default:
                throw new IllegalArgumentException("Constructor not found");
        }
    }

    public Callback getCallback(int var1) {
        CGLIB$BIND_CALLBACKS(this);
        MethodInterceptor var10000;
        switch (var1) {
            case 0:
                var10000 = this.CGLIB$CALLBACK_0;
                break;
            default:
                var10000 = null;
        }

        return var10000;
    }

    public void setCallback(int var1, Callback var2) {
        switch (var1) {
            case 0:
                this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
            default:
        }
    }

    public Callback[] getCallbacks() {
        CGLIB$BIND_CALLBACKS(this);
        return new Callback[]{this.CGLIB$CALLBACK_0};
    }

    public void setCallbacks(Callback[] var1) {
        this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
    }

    static {
        CGLIB$STATICHOOK1();
    }
}

可以看到在代理类的重写方法中，使用了MethodInterceptor拦截器的intercept方法。

java lib应该放哪个文件夹 java的lib_代理类_05