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Here's how Tomcat parses XML and how to create objects by reflection through the example code. The specific code is as follows:

Import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.List;import org.dom4j.Document;import org.dom4j.DocumentException;import org.dom4j.Element;import org.dom4j.io.SAXReader;public class ServerReadXML1 {public static void main (String [] args) throws DocumentException, ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {/ / now if you enter a url-pattern String urlPattern of Servlet in the browser = "/ first" / / get the class name String className = getClassByUrl (urlPattern) according to the urlPattern; / / get the Class object Class clazz = Class.forName (className) based on the full class name; / / create the specified object Object obj = clazz.newInstance () by reflecting the clazz object; / / get the service method Method method = clazz.getDeclaredMethod ("service"); / / get the permission method.setAccessible (true) / / execute service method method.invoke (obj);} private static String getClassByUrl (String urlPattern) throws DocumentException {/ / 1. Create a SAXReader object SAXReader reader = new SAXReader (); / / 2. Read the file Document document = reader.read (ServerReadXML1.class.getClassLoader (). GetResourceAsStream ("web.xml")); / / 3. Get root node Element rootElement = document.getRootElement (); / / System.out.println (rootElement.getName ()); / / 4. Get the child node List servletList = rootElement.elements () under the root node; / / record the content of the same servlet-name tag as urlPattern String servletName = ""; / / record the content of servlet-class in the servlet tag / / servletClassName, that is, the full class name of Servlet String servletClassName = "; / / 5. Traverse the child node for (Element servletElement: servletList) {/ / System.out.println (servletElement.getName ()); / / determine if it is a servlet-mapping tag, execute the code if ("servlet-mapping" .equals (servletElement.getName () {/ / get the url-pattern tag object Element url = servletElement.element ("url-pattern") / / determine whether the content of the tag and the entered urlPattern value are the same if (urlPattern.equals (url.getText () {/ / record the content of the servlet-name tag that is the same as urlPattern / / if it is the same, record ServletName / / get the content of servelt-name in servlet-mapping servletName = servletElement.element ("servlet-name"). GetText () } / / iterate through for (Element servletElement: servletList) {/ / determine if it is a servlet tag Execute this code if ("servlet" .equals (servletElement.getName () {/ / determine whether the value of the servletName obtained in the last traversal is the same as the content of the servlet-name in this traversal (servletName.equals (servletElement.element ("servlet-name"). GetText ()) {/ / if the same record servletClassName servletClassName = servletElement.element ("servlet-class"). GetText () } / / return the full class name of Servlet servletClassName return servletClassName;}}

1. Four ways to obtain Class of reflection

Test public void test1 () throws ClassNotFoundException {/ / 1. Class name. Class Class clazz = String.class; System.out.println (clazz); / / 2. Object .getClass () Class clazz1 = "abc" .getClass (); System.out.println (clazz1); / / 3.Class.forName (); Class clazz2 = Class.forName ("java.lang.String"); System.out.println (clazz2); / / 4.ClassLoader .loadClass ("full class name") Class clazz3 = ReflectTest1.class.getClassLoader (). LoadClass ("java.lang.String"); System.out.println (clazz3);}

two。 Common ways for reflection to use attributes

@ Test public void test2 () throws ClassNotFoundException, NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {/ / get the Class object can get its internal properties Class clazz = Class.forName ("com.atguigu.bean.User"); User user = new User (); / / the getField of the class represented by the Field object can only get the public property Field field = clazz.getField ("email"); System.out.println (field) / / it is not recommended to use Field field2 = clazz.getDeclaredField ("id"); System.out.println (field2); field2.setAccessible (true); field2.setInt (user, 1001); System.out.println (user);}

3. Common methods of using reflection

@ Test public void test3 () throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {Class clazz = Class.forName ("com.atguigu.bean.User"); / / create the object Object obj = clazz.newInstance () by reflection; / / now you want to set the name value String fileName = "name" / / create a method name String methodName = "set" + fileName.substring (0,1). ToUpperCase () / N + fileName.substring (1). ToLowerCase (); / / ame / / get the public method Method method = clazz.getMethod (methodName, String.class) based on the method name; / / execute the specified method method.invoke (obj, "yangjian"); System.out.println (obj);}

Summary

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