聊一聊Java反射

這次提到的Java反射涉及的代碼比較多。因為工作中經常用到反射，對代碼做了很多抽像以及過濾器。雖然代碼量很多，但是簡單易用，過濾插件也易修改。

下面介紹下工作中哪些地方比較容易用到反射。比如插件或者過濾器，如果抽象的子類比較少，配置成XML等結構也是可以達到同樣的效果。如果希望靈活一些，添加了插件或者過濾器代碼子類後希望可以直接使用。可能反射會比較好點，通過掃描所有class或者jar文件，得到所有繼承的子類。如果每次調用都掃描所有的文件會比較影響性能。所以在實現裡面加入反射緩存，對所要獲取反射子類時涉及的所有參數作為一個key緩存所有的反射結果。下次如果是同樣的key，就不在重新掃描。

代碼示例如下：

 public static void main(String[] args) { //設置掃描範圍，可以是class文件所在位置例如bin下或者是mysql開頭或者mysql結尾的jar, //設置為""為全部都掃描,這種比較耗時ReflectUtils.createSharedReflections("classes", "bin", "mysql"); try { //調試階段可以設置每次都全掃描//Beans.setDesignTime(true); final Collection<String> subTypes = ReflectUtils.listSubClass(IA.class);// for (final String subType : subTypes) { //這裡獲取的是所有繼承IA的子類System.out.println(subType); final IA impl = ReflectUtils.initClass(subType, IA.class); if (null == impl) continue; //通過該方式，可以統一做操作， impl.print(); } } catch (Exception e) { e.printStackTrace(); } }

代碼執行結果：

 //緩存文件，避免每次調用反射都重新掃描//如果刪除該文件，再次調用反射時，會重新掃描，一般會在代碼裡面有添加子類的時候會刪除該文件XmlUtils.readXml failure:./configuration.REF (系統找不到指定的文件。)net.simple.reflect.test.Bnet.simple.reflect.test.Bnet.simple.reflect.test.Dnet.simple.reflect.test.V

具體的類裡面如何實現的大家就看下源碼吧，這裡貼出兩個核心類的代碼。源碼地址：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 李岩飛* @email [email protected] * 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 //首先過濾出當前允許掃描的路徑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 李岩飛* @email [email protected] * 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); } /** * 此方法用於綁定一個通用的共享類型遍列工具. * @param sharedReflections */ public static final void setSharedReflections(final Reflections sharedReflections) { ReflectUtils.sharedReflections = sharedReflections; } /** * 調用此方法之前必須先設置共享的類型遍列工具,參考:{@link #setSharedReflections(Reflections)}, * 此方法主要使更方便的遍列給定類的實現, */ public static final Collection<String> listSubClass(final Class<?> baseType, final String... typeNames) {// if (null == sharedReflections) return EMP_COLL; //調用階段由於可能增加新的子類實現,需要每次都重新掃描,只有在發布的產品時使用保存記錄的方法以提高啟動速度. 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; } }}

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。