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1   /*
2    * Copyright 2003-2004 The Apache Software Foundation.
3    * 
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    * 
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    * 
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */ 
16  
17  import org.apache.commons.digester.Digester;
18  
19  /**
20   * A simple program to demonstrate the basic functionality of the
21   * Commons Digester module.
22   * <p>
23   * This code will parse the provided "example.xml" file to build a tree
24   * of java objects, then cause those objects to print out their values
25   * to demonstrate that the input file has been processed correctly.
26   * <p>
27   * As with all code, there are many ways of achieving the same goal;
28   * the solution here is only one possible solution to the problem.
29  * <p> 
30   * Very verbose comments are included here, as this class is intended
31   * as a tutorial; if you look closely at method "addRules", you will
32   * see that the amount of code required to use the Digester is actually
33   * quite low.
34   * <p>
35   * Usage: java Main example.xml
36   */
37  public class Main {
38      
39      /**
40       * Main method : entry point for running this example program.
41       * <p>
42       * Usage: java Example example.xml
43       */
44      public static void main(String  [] args) {
45          if (args.length != 1) {
46              usage();
47              System.exit(-1);
48          }
49          
50          String   filename = args[0];
51          
52          // Create a Digester instance
53          Digester d = new Digester();
54          
55          // Prime the digester stack with an object for rules to
56          // operate on. Note that it is quite common for "this"
57          // to be the object pushed.
58          AddressBook book = new AddressBook();
59          d.push(book);
60          
61          // Add rules to the digester that will be triggered while
62          // parsing occurs.
63          addRules(d);
64          
65          // Process the input file.
66          try {
67              java.io.File   srcfile = new java.io.File  (filename);
68              d.parse(srcfile);
69          }
70          catch(java.io.IOException   ioe) {
71              System.out.println("Error reading input file:" + ioe.getMessage());
72              System.exit(-1);
73          }
74          catch(org.xml.sax.SAXException   se) {
75              System.out.println("Error parsing input file:" + se.getMessage());
76              System.exit(-1);
77          }
78          
79          
80          // Print out all the contents of the address book, as loaded from
81          // the input file.
82          book.print();
83      }
84      
85      private static void addRules(Digester d) {
86  
87          //--------------------------------------------------        
88          // when we encounter a "person" tag, do the following:
89  
90          // create a new instance of class Person, and push that
91          // object onto the digester stack of objects
92          d.addObjectCreate("address-book/person", Person.class);
93          
94          // map *any* attributes on the tag to appropriate
95          // setter-methods on the top object on the stack (the Person
96          // instance created by the preceeding rule). 
97          //
98          // For example:
99          // if attribute "id" exists on the xml tag, and method setId 
100         // with one parameter exists on the object that is on top of
101         // the digester object stack, then a call will be made to that
102         // method. The value will be type-converted from string to
103         // whatever type the target method declares (where possible), 
104         // using the commons ConvertUtils functionality.
105         //
106         // Attributes on the xml tag for which no setter methods exist
107         // on the top object on the stack are just ignored.
108         d.addSetProperties("address-book/person");
109 
110         // call the addPerson method on the second-to-top object on
111         // the stack (the AddressBook object), passing the top object
112         // on the stack (the recently created Person object).
113         d.addSetNext("address-book/person", "addPerson");        
114         
115         //--------------------------------------------------        
116         // when we encounter a "name" tag, call setName on the top
117         // object on the stack, passing the text contained within the
118         // body of that name element [specifying a zero parameter count
119         // implies one actual parameter, being the body text]. 
120         // The top object on the stack will be a person object, because 
121         // the pattern address-book/person always triggers the 
122         // ObjectCreateRule we added previously.
123         d.addCallMethod("address-book/person/name", "setName", 0);
124         
125         //--------------------------------------------------        
126         // when we encounter an "email" tag, call addEmail on the top
127         // object on the stack, passing two parameters: the "type"
128         // attribute, and the text within the tag body.
129         d.addCallMethod("address-book/person/email", "addEmail", 2);
130         d.addCallParam("address-book/person/email", 0, "type");
131         d.addCallParam("address-book/person/email", 1);
132         
133         //--------------------------------------------------        
134         // When we encounter an "address" tag, create an instance of class
135         // Address and push it on the digester stack of objects. After
136         // doing that, call addAddress on the second-to-top object on the
137         // digester stack (a "Person" object), passing the top object on
138         // the digester stack (the "Address" object). And also set things
139         // up so that for each child xml element encountered between the start
140         // of the address tag and the end of the address tag, the text 
141         // contained in that element is passed to a setXXX method on the 
142         // Address object where XXX is the name of the xml element found.
143         d.addObjectCreate("address-book/person/address", Address.class);
144         d.addSetNext("address-book/person/address", "addAddress");
145         d.addSetNestedProperties("address-book/person/address");
146     }
147 
148     private static void usage() {
149         System.out.println("Usage: java Main example.xml");
150     }
151 }
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