快速反射调用

电玩女神 2022-06-16 11:45 146阅读 0赞

java的反射调用比起直接调用要慢很多倍。而反射调用又是被广泛使用的。如何才能提高反射调用的速度呢？

一种想法就是对于每一个bean动态生成一个类，由这个类根据不同的方法名进行直接的方法调用。这样就把反射调用转换成了直接调用，速度应该有很大提高。而动态生成类虽然比较慢，但是在服务器运行期间只运行一次，这个代价还是值得的。

首先需要定义一个IBeanWrapper。这个wrapper负责进行反射调用到直接调用的转换。每个bean类会有一个自己的wrapper类实现。

public interface IBeanWrapper {
    	public void setValue(Object obj, String field, Object value);
    	
    	public Object getValue(Object obj, String field);
    }

然后是BeanWrapperFactory，负责获取wrapper的类实例。

public class BeanWrapperFactory {
    	private static Map<Class, IBeanWrapper> wrappers = new HashedMap();
    	
    	public static IBeanWrapper getBeanWrapper(Class clz) {
    		IBeanWrapper inst = wrappers.get(clz);
    		if (inst == null) {
    			File outFile = new File(System.getProperties("java.io.temp"), "wrappers");
    			if (!outFile.exists()) {
    				outFile.mkdirs();
    			}
    			String s = new BeanWrapperFactory().getCode(UserEx.class);
    			CompilerUtil.compile(outFile.getAbsolutePath(), clz.getSimpleName()+"Wrapper", s);
    		
    			DynamicClassLoader cl = new DynamicClassLoader(outFile);
    			try {
    				inst = (IBeanWrapper)cl.loadClass("com.temp.wrapper."+clz.getSimpleName()+"Wrapper").newInstance();
    			} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
    				e.printStackTrace();
    			}
    			wrappers.put(clz, inst);
    		}
    		return inst;
    	}
    
    	public String getCode(Class clz) {
    		StringBuffer sb = new StringBuffer();
    		
    		sb.append("package com.temp.wrapper;\n");
    		sb.append("public class "+clz.getSimpleName()+"Wrapper implements IBeanWrapper {\n");
    		
    		sb.append("public void setValue(Object obj, String field, Object value) {\n");
    		sb.append("  "+clz.getName()+" o = ("+clz.getName()+")obj;\n");
    		sb.append("  switch(field.hashCode()) {\n");
    		List<Field> fields = ReflectionUtils.getDeclaredFields(clz);
    		for (int i = 0 ; i < fields.size() ; i++) {
    			Field field = fields.get(i); 
    			String name = field.getName();
    			String methodName = StringUtils.capitalise(name);
    			String type = getType(field.getType());
    			if ("id".equals(name)) {
    				try {
    					type = getType(clz.getMethod("getId").getReturnType());
    				} catch (NoSuchMethodException | SecurityException e) {
    					e.printStackTrace();
    				}
    			}
    			
    			sb.append("    case ").append(Integer.toString(name.hashCode())).append(":\n");
    			if (field.getType() == int.class) {
    				sb.append("    o.set").append(methodName).append("(((Number)value).intValue());\n");
    			} else if (field.getType() == long.class) {
    				sb.append("    o.set").append(methodName).append("(((Number)value).longValue());\n");
    			} else if (field.getType() == double.class) {
    				sb.append("    o.set").append(methodName).append("(((Number)value).doubleValue());\n");
    			} else if (field.getType() == byte.class) {
    				sb.append("    o.set").append(methodName).append("(((Number)value).byteValue());\n");
    			} else if (field.getType() == float.class) {
    				sb.append("    o.set").append(methodName).append("(((Number)value).floatValue());\n");
    			} else if (field.getType() == boolean.class) {
    				sb.append("    o.set").append(methodName).append("(((Boolean)value).booleanValue());\n");
    			} else if (field.getType() == char.class) {
    				sb.append("    o.set").append(methodName).append("(((Character)value).charValue());\n");
    			} else if (field.getType() == byte[].class) {
    				sb.append("    o.set").append(methodName).append("((byte[])value);\n");
    			} else {
    				sb.append("    o.set").append(methodName).append("((").append(type).append(")value);\n");
    			}
    			sb.append("    break;\n");
    		}
    		sb.append("  }\n");
    		sb.append("}\n\n");
    		
    		sb.append("public Object getValue(Object obj, String field) {\n");
    		sb.append("  "+clz.getName()+" o = ("+clz.getName()+")obj;\n");
    		sb.append("  switch(field.hashCode()) {\n");
    		for (int i = 0 ; i < fields.size() ; i++) {
    			Field field = fields.get(i); 
    			String name = field.getName();
    			String methodName = StringUtils.capitalise(name);
    			sb.append("    case ").append(Integer.toString(name.hashCode())).append(":\n");
    			if (field.getType() == boolean.class) {
    				sb.append("    return o.is").append(methodName).append("();\n");
    			} else {
    				sb.append("    return o.get").append(methodName).append("();\n");
    			}
    		}
    		sb.append("  }\n");
    		sb.append("  throw new RuntimeException(\"field not found:\"+field);\n");
    		sb.append("}");
    		sb.append("}");
    		return sb.toString();
    	}
    	
    	private String getType(Class clz) {
    		if (clz == boolean.class) {
    			return "boolean";
    		} else if (clz == int.class) {
    			return "int";
    		} else if (clz == long.class) {
    			return "long";
    		} else if (clz == double.class) {
    			return "double";
    		} else if (clz == byte.class) {
    			return "byte";
    		} else if (clz == float.class) {
    			return "float";
    		} else {
    			return clz.getName();
    		}
    	}
    }

其中静态方法

public static IBeanWrapper getBeanWrapper(Class clz)

负责获取一个给定类的wrapper实例。getCode()方法负责生成wrapper类的源代码。然后CompilerUtil进行编译，然后动态装载。静态变量wrappers用于缓存类对应的wrapper实例。为了提高速度，生成代码中没使用属性名字符串比较，而是直接用属性名的hash值比较。

DynamicClassLoader用于动态装载类。

public class DynamicClassLoader extends URLClassLoader {
    	public DynamicClassLoader(File... files)//, ClassLoader parent) 
    	{
    		super(getUrls(files));//, parent);
    	}
    
    	public DynamicClassLoader(ClassLoader parent, File... files) 
    	{
    		super(getUrls(files), parent);
    	}
    	
    	private static final URL[] getUrls(File... files) {
    		URL[] urls = new URL[files.length];
    		try{
    			int i = 0;
    			for(File file : files) {
    				urls[i] = file.toURI().toURL();
    			}
    		}catch(Exception ex){
    		}
    		return urls;
    	}
    }
    
     
     
     
     动态编译类CompilerUtil可以参考点击打开链接
     
     下面写段程序测试一下性能：
     
     		IBeanWrapper inst = new BeanWrapperFactory().getBeanWrapper(UserEx.class);
    		User u = new User();
    		Method method = User.class.getMethod("setUserCode", String.class);
    		
    		long t0 = System.currentTimeMillis();
    		for (int i = 0 ; i < 100000000 ; i++) {
    			u.setUserCode("123");
    		}
    		long t1 = System.currentTimeMillis();
    		for (int i = 0 ; i < 100000000 ; i++) {
    			inst.setValue(u, "userCode", "123");
    		}		
    		long t2 = System.currentTimeMillis();
    		for (int i = 0 ; i < 100000000 ; i++) {
    			try {
    				method.invoke(u, "123");
    			} catch (IllegalArgumentException e) {
    				e.printStackTrace();
    			} catch (InvocationTargetException e) {
    				e.printStackTrace();
    			}
    		}
    		long t3 = System.currentTimeMillis();
    		
    		System.out.println("time:"+(t1 - t0)+", "+(t2 - t1)+", "+(t3 - t2));
    输出为：
     
     time:396, 3480, 15499
     即快速反射调用大约是直接调用的9倍，是反射调用的1/5。提高还是很大的。这还是Method对象被缓存的情况下。如果不缓存Method对象，
     
                     IBeanWrapper inst = new BeanWrapperFactory().getBeanWrapper(UserEx.class);
    		UserEx u = new UserEx();
    		Double d = new Double(123D);
    		
    		long t0 = System.currentTimeMillis();
    		for (int i = 0 ; i < 100000000 ; i++) {
    			u.setD5(d);
    		}
    		long t1 = System.currentTimeMillis();
    		for (int i = 0 ; i < 100000000 ; i++) {
    			inst.setValue(u, "userCode", "123");
    		}		
    		long t2 = System.currentTimeMillis();
    		for (int i = 0 ; i < 100000000 ; i++) {
    			try {
    				Method method = UserEx.class.getMethod("setUserCode", String.class);
    				method.invoke(u, "123");
    			} catch (IllegalArgumentException e) {
    				e.printStackTrace();
    			} catch (InvocationTargetException e) {
    				e.printStackTrace();
    			}
    		}
    		long t3 = System.currentTimeMillis();
    		
    		System.out.println("time:"+(t1 - t0)+", "+(t2 - t1)+", "+(t3 - t2));
    
     
     输出为
     time:314, 3777, 246019
     快速反射调用大约是反射调用的1/62。