Java运行时动态加载类之ClassLoader

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需求场景：动态加载类ClassLoaderd，在xml文件中配置加载类名称和方法，：

一、准备

1）在D:\\tmp\\目录下配置a.xml文件：

<?xml version="1.0" encoding="ISO-8859-1"?><classes> <class name="User">  <method>say</method>  </class>  <class name="map">  <method>add</method>  </class> </classes>

2）要动态加载的类：

package dx;public class map {public void add(){System.out.println("1+1=2");}}

package cn.fjs;public class User {public void say(){System.out.println(" hello ...");} }

对这两个类进行编译后，将class文件复制到D:\\tmp\\路径下。

二、参考代码如下

1、重载ClassLoader类：

package cn.fjs;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;public class DynamicClassLoader extends ClassLoader{private static final String SUFFIX = ".class";public String[] paths;public DynamicClassLoader(String[] paths) {this.paths = paths;}public DynamicClassLoader(ClassLoader parent,String[] paths){super(parent);this.paths = paths;}@SuppressWarnings("deprecation")@Overrideprotected Class<?> findClass(String className) throws ClassNotFoundException { String classPath = getClassPath(className);if(classPath != null){byte[] clazz = loadClazz(classPath);return defineClass(clazz, 0, clazz.length); }else{System.out.println("class is not found !");return null;}} public byte[] loadClazz(String classPath) { try { FileInputStream in = new FileInputStream(new File(classPath));ByteArrayOutputStream baos = new ByteArrayOutputStream();int b;while((b = in.read()) != -1){baos.write(b);}in.close();return baos.toByteArray();} catch (Exception e) {System.out.println(e);}return null;}public String getClassPath(String className){for(String path : paths){if(className.contains(".")){className = className.replaceAll(".", File.separator);}String classPath = path + className + SUFFIX; File classFile = new File(classPath);if(classFile.exists()){return classPath;}}return null;}}

2、解析xml文件

package cn.fjs;import java.io.IOException;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import javax.xml.parsers.ParserConfigurationException;import org.w3c.dom.Document;import org.w3c.dom.Element; import org.w3c.dom.Node;import org.w3c.dom.NodeList;import org.xml.sax.SAXException; //解析xml文件，获取类和方法public class DynamicDom {private static DocumentBuilderFactory dbFactory = null;      private static DocumentBuilder db = null;      private static Document document = null;          static{          try {              dbFactory = DocumentBuilderFactory.newInstance();              db = dbFactory.newDocumentBuilder();          } catch (ParserConfigurationException e) {              e.printStackTrace();          }      }             public Map<String,List<String>> getMethods(String fileName) throws SAXException, IOException{      Map<String,List<String>> classes = new HashMap<String, List<String>>();    document = db.parse(fileName);      NodeList nList = document.getElementsByTagName("class");    for(int i = 0 ; i<nList.getLength();i++){     Node node = nList.item(i);     Element ele = (Element)node;     if(node.getNodeType() == Element.ELEMENT_NODE){      String clazz = ele.getAttribute("name");       List<String> methods = new ArrayList<String>();      String method = ele.getElementsByTagName("method").item(0).getTextContent();      methods.add(method);      classes.put(clazz, methods);       }    }    return classes;    } }

3、测试类：

package cn.fjs;import java.util.List;import java.util.Map;import cn.fjs.DynamicClassLoader;import cn.fjs.DynamicDom;public class DynamicClassLoaderTest {public static void main(String[] args) {DynamicDom dmo = new DynamicDom();//xml文件解析类Map<String, List<String>> classes;    //重载ClassLoader类DynamicClassLoader loader = new DynamicClassLoader(new String[]{"D:\\tmp\\"}); try {classes = dmo.getMethods("D:\\tmp\\a.xml");for(String key:classes.keySet()){ for(String clazz : classes.get(key)){ Class<?> c =loader.findClass(key);//类名字c.getMethod(clazz).invoke(c.newInstance());//方法名字}} }catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

执行结果：

 hello ...1+1=2

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