Tomcat parsing XML and reflection to create objects principle
1 import java.lang.reflect.InvocationTargetException;
2 import java.lang.reflect.Method;
3 import java.util.List;
4
5 import org.dom4j.Document;
6 import org.dom4j.DocumentException;
7 import org.dom4j.Element;
8 import org.dom4j.io.SAXReader;
9
10 public class ServerReadXML1 {
11
12 public static void main(String[] args)
13 throws DocumentException, ClassNotFoundException, InstantiationException, IllegalAccessException,
14 A NoSuchMethodException, a SecurityException, an IllegalArgumentException, a InvocationTargetException {
15
16 // now Servlet If the input in a browser-pattern URL
. 17 String urlPattern = " / First " ;
18 is
. 19 // The class name acquired urlPattern
20 is String className = getClassByUrl (urlPattern );
21 is
22 is // Get class object based on the full class name
23 is class = clazz the Class.forName (className);
24
25 // create the specified object reflected by the object clazz
26 is Object obj = clazz.newInstance ();
27
28 // Get service method
29 Method, Method clazz.getDeclaredMethod = ( " service " );
30
31 is // Get Permissions
32 method.setAccessible ( to true );
33 is
34 is // perform service method
35 Method.invoke (obj);
36
37 [ }
38 is
39 Private static String getClassByUrl (String urlPattern) throws DocumentException {
40
41 is // 1. Create an object SAXReader
42 is SAXReader Reader = new newSAXReader ();
43 is
44 is // 2. read the file
45 the Document Document reader.Read = (ServerReadXML1. Class .getClassLoader () the getResourceAsStream (. " The web.xml " ));
46 is
47 // 3. Get root
48 the Element = the rootElement document.getRootElement ();
49 // System.out.println (rootElement.getName ());
50
51 is // 4. acquisition sub-nodes below the root node
52 is List <the Element> servletList = rootElement.elements ();
53 is
54 is // content recorded in the same servlet-name tag urlPattern
55 ServletName = String "" ;
56 is
57 is // recorded content servlet-class of tag servlet
58 // content of servletClassName Servlet is full class name
59 String servletClassName = "" ;
60
61 is // 5. The traverse the child nodes
62 for (the Element servletElement: servletList) {
63 is // System.out.println (servletElement.getName ());
64
65 // determines if the label is a servlet-mapping, the execution code
66 IF ( " servlet-mapping " .equals ( servletElement.getName ())) {
67
68 // Get the object tag url-pattern
69 the Element URL = servletElement.element ( " url-pattern " );
70
71 is // determine the content of the tag and the values are the same urlPattern
72 IF (urlPattern.equals (url.getText () )) {
73 is
74 // record the same content urlPattern servlet-name tag
75 // if the same, then the recording servletName
76 // content acquisition servlet-mapping of the servelt-name
77 servletName = servletElement.element ( " the servlet -name " ) .getText ();
78
79 }
80
81 }
82
83 }
84
85 // iterate again to
86 for (the Element servletElement: servletList) {
87 // determines if the servlet label, this code is executed
88 IF ( " servlet " .equals (servletElement.getName ())) {
89
90 // value judgment on a traversal acquired servletName and the content traversing the servlet-name is the same as
91 iF (servletName.equals (servletElement.element ( " servlet-name " ) .getText ())) {
92
93 // if the same recording servletClassName
94 servletClassName = servletElement.element("servlet-class").getText();
95
96 }
97
98 }
99
100 }
101
102 // 返回Servlet的全类名 servletClassName
103 return servletClassName;
104 }
105
106 }
1. Get Class 4 ways reflected
@Test
public void test1() throws ClassNotFoundException {
//1.类名.class
Class clazz = String.class;
System.out.println(clazz);
//2.对象.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("全类名")
Class clazz3 = ReflectTest1.class.getClassLoader().loadClass("java.lang.String");
System.out.println(clazz3);
}
2.反射使用属性的常用方法
@Test
public void test2() throws ClassNotFoundException, NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
//获取Class对象 可以获取其内部的属性
Class clazz = Class.forName("com.atguigu.bean.User");
User user = new User();
//Field对象 代表中类的属性 getField只能获取公共属性
Field field = clazz.getField("email");
System.out.println(field);
//此种方式破坏代码的封装性 不推荐使用
Field field2 = clazz.getDeclaredField("id");
System.out.println(field2);
field2.setAccessible(true);
field2.setInt(user, 1001);
System.out.println(user);
}
3.反射使用方法的常用方法
@Test
public void test3() throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {
Class clazz = Class.forName("com.atguigu.bean.User");
//通过反射创建对象
Object obj = clazz.newInstance();
//现在想要设置name值
String fileName = "name";
//创建一个方法名
String methodName = "set" + fileName.substring(0, 1).toUpperCase() //N
+ fileName.substring(1).toLowerCase(); //ame
//根据方法名 获取公共方法
Method method = clazz.getMethod(methodName, String.class);
//执行指定的方法
method.invoke(obj, "yangjian");
System.out.println(obj);
}