工作中常用到的Java反射

学习java的同学注意了！！！ 学习过程中遇到什么问题或者想获取学习资源的话，欢迎加入Java学习交流群，群号码：183993990  我们一起学Java！

这次提到的Java反射涉及的代码比较多。因为工作中经常用到反射，对代码做了很多抽象以及过滤器。虽然代码量很多，但是简单易用，过滤插件也易修改。

下面介绍下工作中哪些地方比较容易用到反射。比如插件或者过滤器，如果抽象的子类比较少，配置成xml等结构也是可以达到同样的效果。如果希望灵活一些，添加了插件或者过滤器代码子类后希望可以直接使用。可能反射会比较好点，通过扫描所有class或者jar文件，得到所有继承的子类。如果每次调用都扫描所有的文件会比较影响性能。所以在实现里面加入反射缓存，对所要获取反射子类时涉及的所有参数作为一个key缓存所有的反射结果。下次如果是同样的key，就不在重新扫描。

代码示例如下：

public static void main(String[] args) {		//设置扫描范围，可以是class文件所在位置例如bin下或者是MySQL开头或者mysql结尾的jar,		//设置为""为全部都扫描,这种比较耗时		ReflectUtils.createSharedReflections("classes", "bin", "mysql");		try {			//调试阶段可以设置每次都全扫描			//Beans.setDesignTime(true);			final Collection<String> subTypes = ReflectUtils.listSubClass(IA.class);//			for (final String subType : subTypes) {				//这里获取的是所有继承IA的子类				System.out.PRintln(subType);				final IA impl = ReflectUtils.initClass(subType, IA.class);				if (null == impl)					continue;				//通过该方式，可以统一做操作，				impl.print();			}		} catch (Exception e) {			e.printStackTrace();		}	}
代码执行结果：
//缓存文件，避免每次调用反射都重新扫描//如果删除该文件，再次调用反射时，会重新扫描，一般会在代码里面有添加子类的时候会删除该文件XmlUtils.readXml failure:./configuration.REF (系统找不到指定的文件。)net.simple.reflect.test.Bnet.simple.reflect.test.Bnet.simple.reflect.test.Dnet.simple.reflect.test.V
具体的类里面如何实现的大家就看下源码吧，这里贴出两个核心类的代码。源码地址：https://git.oschina.net/eliyanfei/api_tools
package net.simple.reflect;import java.io.File;import java.io.IOException;import java.net.JarURLConnection;import java.net.URL;import java.net.URLDecoder;import java.util.ArrayList;import java.util.Collection;import java.util.Enumeration;import java.util.LinkedHashMap;import java.util.List;import java.util.Map;import java.util.concurrent.TimeUnit;import java.util.jar.JarEntry;import java.util.jar.JarFile;import java.util.zip.ZipEntry;import net.simple.reflect.filter.IPathURLFilter;import net.simple.reflect.filter.ISubTypeFilter;import net.simple.reflect.filter.ITypeFilter;import org.w3c.dom.Document;import org.w3c.dom.Element;/** *  * @author 李岩飞 * @email eliyanfei@126.com	 * 2016年11月2日 下午3:23:49 * */public final class Reflections {	private final Collection<URL> pathUrls;	private final Collection<IPathURLFilter> pathURLfilters;	private final Collection<ITypeFilter> typeFilters;	private ISubTypeFilter subTypeFilter;	public Reflections() {		typeFilters = new ArrayList<ITypeFilter>();		pathURLfilters = new ArrayList<IPathURLFilter>();		this.pathUrls = ClasspathHelper.getUrlsForCurrentClasspath();	}	public Reflections(final Collection<URL> pathUrls) {		this.pathUrls = pathUrls;		typeFilters = new ArrayList<ITypeFilter>();		pathURLfilters = new ArrayList<IPathURLFilter>();	}	/**	 * @param subTypeFilter	 *            the subTypeFilter to set	 */	public void setSubTypeFilter(final ISubTypeFilter subTypeFilter) {		this.subTypeFilter = subTypeFilter;	}	/**	 * @return the subTypeFilter	 */	public ISubTypeFilter getSubTypeFilter() {		return subTypeFilter;	}	public Reflections addPathURLFilter(final IPathURLFilter pathURLFilter) {		if (null == pathURLFilter)			return this;		if (!this.pathURLfilters.contains(pathURLFilter))			this.pathURLfilters.add(pathURLFilter);		return this;	}	public Reflections addTypeFilter(final ITypeFilter typeFilter) {		if (null == typeFilter)			return this;		if (!this.typeFilters.contains(typeFilter))			this.typeFilters.add(typeFilter);		return this;	}	private static final String histFile = "./configuration.REF";	private Document histDom;	public Collection<String> getSubTypesFast(final Class<?> baseType) {//, final String... typeNames		//首先过滤出当前允许扫描的路径		final StringBuilder bufPathsId = new StringBuilder(32);		final Map<File, URL> fileUrls = new LinkedHashMap<File, URL>(8);		for (final URL pathUrl : pathUrls) {			if (!acceptPathUrl(pathUrl))				continue;			File file = null;			try {				file = new File(URLDecoder.decode(pathUrl.getFile(), "UTF-8"));			} catch (final Exception e) {				file = new File(pathUrl.getFile());			}			fileUrls.put(file, pathUrl);			if (!file.exists())//is url file?ignore				continue;			bufPathsId.append(file.getName()).append(file.lastModified());		}		final String domId = md5.getHashString(bufPathsId.toString());		if (null == histDom)			histDom = W3cUtils.readXml(histFile);		if (null == histDom)			histDom = W3cUtils.newDom("R");		Element rootEle = histDom.getDocumentElement();		if (null == rootEle)			histDom.appendChild(rootEle = histDom.createElement("R"));		if (!domId.equals(rootEle.getAttribute("id"))) {			rootEle.getParentNode().removeChild(rootEle);			histDom.appendChild(rootEle = histDom.createElement("R"));			rootEle.setAttribute("id", domId);		}		final String baseTypeId = MD5.getHashString(baseType.getName());		Element refEle = W3cUtils.firstChildElement(rootEle, "E", "id", baseTypeId);		if (null != refEle) {			final List<Element> valueEles = W3cUtils.childElementList(refEle, "F");			final Collection<String> result = new ArrayList<String>(valueEles.size());			for (final Element valueEle : valueEles) {				result.add(new String(Base64.decodeFast(valueEle.getAttribute("id"))));			}			return result;		}		final ThreadPool<ListSubTypes> pool = new ThreadPool<ListSubTypes>();		for (final File fileKey : fileUrls.keySet()) {			pool.execute(new ListSubTypes(baseType, fileKey, fileUrls.get(fileKey)));		}		try {			pool.shutdown(3, TimeUnit.MINUTES);		} catch (final InterruptedException e) {			e.printStackTrace();//for debug		}		final Collection<String> result = new ArrayList<String>();		for (final ListSubTypes task : pool.getThreadRunables()) {			result.addAll(task.result);		}		refEle = W3cUtils.addEle(rootEle, "E");		refEle.setAttribute("id", baseTypeId);		for (final String itm : result) {			W3cUtils.addEle(refEle, "F").setAttribute("id", Base64.encodeToString(itm.getBytes(), false));		}		try {			W3cUtils.writeXmlDocument(histFile, histDom);		} catch (final Exception e) {		}		return result;	}	/**	 * @see {@link ReflectUtils#createSharedReflections(String...)}	 * @see {@link ReflectUtils#setSharedReflections(Reflections)}	 * @see {@link ReflectUtils#listSubClass(Class)}	 * @param baseType	 * @return	 */	public Collection<String> getSubTypes(final Class<?> baseType, final String... typeNames) {//		final ThreadPool<ListSubTypes> pool = new ThreadPool<ListSubTypes>();		for (final URL pathUrl : pathUrls) {			if (!acceptPathUrl(pathUrl))				continue;			File file = null;			try {				file = new File(URLDecoder.decode(pathUrl.getFile(), "UTF-8"));			} catch (final Exception e) {				file = new File(pathUrl.getFile());			}			pool.execute(new ListSubTypes(baseType, file, pathUrl, typeNames));		}		try {			pool.shutdown(3, TimeUnit.MINUTES);		} catch (final InterruptedException e) {			e.printStackTrace();//for debug		}		final Collection<String> result = new ArrayList<String>();		for (final ListSubTypes task : pool.getThreadRunables()) {			result.addAll(task.result);		}		return result;	}	class ListSubTypes implements Runnable {		final File file;		final Class<?> baseType;		final URL pathUrl;		final String[] typeNames;		public ListSubTypes(final Class<?> baseType, final File file, final URL pathUrl, final String... typeNames) {			this.baseType = baseType;			this.file = file;			this.pathUrl = pathUrl;			this.typeNames = typeNames;		}		Collection<String> result = new ArrayList<String>(4);		@Override		public void run() {			if (file.isDirectory()) {				listSubTypesFromDirectory(file, baseType, pathUrl, file, result, typeNames);			} else				listSubTypesFromJar(baseType, pathUrl, result, typeNames);		}	}	/**	 * @param baseType	 * @param pathUrl	 * @param result	 */	public void listSubTypesFromDirectory(final File baseDirectory, final Class<?> baseType, final URL pathUrl, final File directory,			final Collection<String> result, final String... typeNames) {		File[] files = directory.listFiles();		if (null == files)			files = new File[] {};		String clazzPath;		final int baseDirLen = baseDirectory.getAbsolutePath().length() + 1;		for (final File file : files) {			if (file.isDirectory()) {				listSubTypesFromDirectory(baseDirectory, baseType, pathUrl, file, result, typeNames);			} else {				clazzPath = file.getAbsolutePath().substring(baseDirLen);				clazzPath = clazzPath.replace('//', '/');				doTypesFilter(baseType, pathUrl, result, clazzPath, typeNames);			}		}	}	/**	 * @param baseType	 * @param pathUrl	 * @param result	 */	public void listSubTypesFromJar(final Class<?> baseType, URL pathUrl, final Collection<String> result, final String... typeNames) {		try {			// It does not work with the filesystem: we must			// be in the case of a package contained in a jar file.			JarFile jarFile = null;			try {				if ("file".equals(pathUrl.getProtocol()))					pathUrl = new URL("jar:" + pathUrl.toExternalForm() + "!/");				jarFile = ((JarURLConnection) pathUrl.openConnection()).getJarFile();			} catch (final Exception e) {				final String filePath = pathUrl.getFile();				// if on win platform				if (filePath.indexOf(':') != -1) {					if (pathUrl.getFile().charAt(0) == '/')						jarFile = new JarFile(filePath.substring(1));				}				if (null == jarFile)					jarFile = new JarFile(filePath);			}			final Enumeration<JarEntry> e = jarFile.entries();			ZipEntry entry;			while (e.hasMoreElements()) {				entry = e.nextElement();				doTypesFilter(baseType, pathUrl, result, entry.getName(), typeNames);			}		} catch (final IOException ioex) {		}	}	private void doTypesFilter(final Class<?> baseType, final URL pathUrl, final Collection<String> result, final String clazzPath,			final String... typeNames) {		if (!clazzPath.endsWith(".class"))			return;		final int lastDotIdx = clazzPath.lastIndexOf('.');		if (-1 == lastDotIdx)			return;		final String typeDef = clazzPath.substring(0, lastDotIdx).replace('/', '.');		if (null != typeNames && typeNames.length > 0) {			final int lastDot = typeDef.lastIndexOf('.');			if (lastDot == -1)				return;			final String typeName = typeDef.substring(lastDot + 1);			boolean withLiked = false;			for (final String tmpTypeName : typeNames) {				if (!typeName.contains(tmpTypeName))					continue;				withLiked = true;				break;			}			if (withLiked == false)				return;		}		if (this.typeFilters.isEmpty()) {			if (null == this.subTypeFilter || this.subTypeFilter.accept(baseType, pathUrl, clazzPath))				result.add(typeDef);		} else {			for (final ITypeFilter typeFilter : this.typeFilters) {				if (!typeFilter.accept(clazzPath))					continue;				if (null == this.subTypeFilter || this.subTypeFilter.accept(baseType, pathUrl, clazzPath))					result.add(typeDef);			}		}	}	/**	 * @param pathUrl	 * @return	 */	private boolean acceptPathUrl(final URL pathUrl) {		if (this.pathURLfilters.isEmpty())			return true;		for (final IPathURLFilter pathURLFilter : this.pathURLfilters) {			if (pathURLFilter.accept(pathUrl))				return true;		}		return false;	}}
package net.simple.reflect;import java.beans.Beans;import java.io.File;import java.io.IOException;import java.io.UnsupportedEncodingException;import java.net.JarURLConnection;import java.net.URL;import java.net.URLDecoder;import java.util.ArrayList;import java.util.Collection;import java.util.Collections;import java.util.Enumeration;import java.util.List;import java.util.jar.JarEntry;import java.util.jar.JarFile;import java.util.zip.ZipEntry;import net.simple.reflect.filter.PathURLFilter;import net.simple.reflect.filter.SampleSubInstanceFilter;import net.simple.reflect.filter.TypeFilter;/** *  * @author 李岩飞 * @email eliyanfei@126.com	 * 2016年11月2日 下午3:24:02 * */public final class ReflectUtils {	public static final String VAR_START_FLAG = "${";	public static final String VAR_END_FLAG = "}";	private static Reflections sharedReflections;	static final Collection<String> EMP_COLL = Collections.emptyList();	public static final void createSharedReflections(final String... filterExts) {		final Reflections refs = new Reflections();		refs.addPathURLFilter(new PathURLFilter(filterExts));//		refs.addTypeFilter(TypeFilter.DEFAULT);		refs.setSubTypeFilter(SampleSubInstanceFilter.DEFAULT);		ReflectUtils.setSharedReflections(refs);	}	/**	 * 此方法用于绑定一个通用的共享类型遍列工具.	 * @param sharedReflections	 */	public static final void setSharedReflections(final Reflections sharedReflections) {		ReflectUtils.sharedReflections = sharedReflections;	}	/**	 * 调用此方法之前必须先设置共享的类型遍列工具,参考:{@link #setSharedReflections(Reflections)},	 * 此方法主要使更方便的遍列给定类的实现,	 */	public static final Collection<String> listSubClass(final Class<?> baseType, final String... typeNames) {//		if (null == sharedReflections)			return EMP_COLL;		//调用阶段由于可能增加新的子类实现,需要每次都重新扫描,只有在发布的产品时使用保存记录的方法以提高启动速度.		return Beans.isDesignTime() ? sharedReflections.getSubTypes(baseType, typeNames) : sharedReflections.getSubTypesFast(baseType);	}	public static List<Class<?>> listClassOfPackage(final Class<?> cType, final String extenion) {		final List<Class<?>> result = new ArrayList<Class<?>>();		final List<String> cPath = ReflectUtils.listClassCanonicalNameOfPackage(cType, extenion);		for (final String path : cPath) {			try {				result.add(Class.forName(path, false, Thread.currentThread().getContextClassLoader()));			} catch (final Exception e) {				// ignore			}		}		return result;	}	public static List<String> listClassCanonicalNameOfPackage(final Class<?> clazz, final String extenion) {		return ReflectUtils.listNameOfPackage(clazz, extenion, true);	}	public static List<String> listClassNameOfPackage(final Class<?> clazz, final String extenion) {		return ReflectUtils.listNameOfPackage(clazz, extenion, false);	}	public static List<String> listNameOfPackage(final Class<?> clazz, final String extenion, final boolean fullPkgName) {		return ReflectUtils.listNameOfPackage(clazz.getName().replace('.', '/') + ".class", extenion, fullPkgName);	}	public static List<String> listNameOfPackage(final String clazzPkg, final String extenion, final boolean fullPkgName) {		final List<String> result = new ArrayList<String>();		final StringBuffer pkgBuf = new StringBuffer(clazzPkg);		if (pkgBuf.charAt(0) != '/')			pkgBuf.insert(0, '/');		final URL urlPath = ReflectUtils.class.getResource(pkgBuf.toString());		if (null == urlPath)			return result;		String checkedExtenion = extenion;		if (!extenion.endsWith(".class"))			checkedExtenion = extenion + ".class";		if (pkgBuf.toString().endsWith(".class"))			pkgBuf.delete(pkgBuf.lastIndexOf("/"), pkgBuf.length());		pkgBuf.deleteCharAt(0);		final StringBuffer fileUrl = new StringBuffer();		try {			fileUrl.append(URLDecoder.decode(urlPath.toExternalForm(), "UTF-8"));		} catch (final UnsupportedEncodingException e1) {			fileUrl.append(urlPath.toExternalForm());		}		if (fileUrl.toString().startsWith("file:")) {			fileUrl.delete(0, 5);// delete file: flag			if (fileUrl.indexOf(":") != -1)				fileUrl.deleteCharAt(0);// delete flag			final String baseDir = fileUrl.substring(0, fileUrl.lastIndexOf("classes") + 8);			ReflectUtils.doListNameOfPackageInDirectory(new File(baseDir), new File(baseDir), result, pkgBuf.toString(), checkedExtenion, fullPkgName);		} else {			ReflectUtils.doListNameOfPackageInJar(urlPath, urlPath, result, pkgBuf.toString(), checkedExtenion, fullPkgName);		}		return result;	}	/**	 */	private static void doListNameOfPackageInJar(final URL baseUrl, final URL urlPath, final List<String> result, final String clazzPkg, final String extenion, final boolean fullPkgName) {		try {			// It does not work with the filesystem: we must			// be in the case of a package contained in a jar file.			final JarURLConnection conn = (JarURLConnection) urlPath.openConnection();			final JarFile jfile = conn.getJarFile();			final Enumeration<JarEntry> e = jfile.entries();			ZipEntry entry;			String entryname;			while (e.hasMoreElements()) {				entry = e.nextElement();				entryname = entry.getName();				if (entryname.startsWith(clazzPkg) && entryname.endsWith(extenion)) {					if (fullPkgName)						result.add(entryname.substring(0, entryname.lastIndexOf('.')).replace('/', '.'));					else						result.add(entryname.substring(entryname.lastIndexOf('/') + 1, entryname.lastIndexOf('.')));				}			}		} catch (final IOException ioex) {		}	}	private static void doListNameOfPackageInDirectory(final File baseDirectory, final File directory, final List<String> result, final String clazzPkg, final String extenion,			final boolean fullPkgName) {		File[] files = directory.listFiles();		if (null == files)			files = new File[] {};		String clazzPath;		final int baseDirLen = baseDirectory.getAbsolutePath().length() + 1;		for (final File file : files) {			if (file.isDirectory()) {				ReflectUtils.doListNameOfPackageInDirectory(baseDirectory, file, result, clazzPkg, extenion, fullPkgName);			} else {				if (!file.getName().endsWith(extenion))					continue;				if (fullPkgName) {					clazzPath = file.getAbsolutePath().substring(baseDirLen);					clazzPath = clazzPath.substring(0, clazzPath.length() - 6);					result.add(clazzPath.replace(File.separatorChar, '.'));				} else {					result.add(file.getName().substring(0, file.getName().length() - 6));				}			}		}	}	public static final <T> T initClass(final String implClass, final Class<T> tType) {		return ReflectUtils.initClass(implClass, tType, true);	}	public static final <T> T initClass(final String implClass, final Class<T> tType, final boolean doInit) {		try {			final Object object = Class.forName(implClass, doInit, Thread.currentThread().getContextClassLoader()).newInstance();			return tType.cast(object);		} catch (final Throwable e) {			return null;		}	}}
学习Java的同学注意了！！！ 学习过程中遇到什么问题或者想获取学习资源的话，欢迎加入Java学习交流群，群号码：183993990  我们一起学Java！