Tomcat4 源代码分析 （15） How Tomcat Works 第十五章
Chapter 15 : Digester
概览
在之前的章节中，我们用Bootstrap类来实例化connector, context, wrappers 以及其他的组件。当把组件注入到父级组件中时，我们使用的是set方法，比如说：
connector.setContainer(context);
context.setPath("/myApp");
context.setDocBase("myApp");
再比如说：
context.setLoader(loader);
context.addChild(wrapper1);
context.addChild(wrapper2);
这种注入方式的缺点是不灵活，改动时需要动源代码。Tomcat4使用了更加灵活的方式，即使用xml配置文件的方法。
Digester
Digester是一个开源的项目，解析xml文件，然后把里面的element变为java object。
下面给出三个小例子，很容易了解digester的使用方法\
Example 1 :
employee1.xml
<?xml version="1.0" encoding="ISO-8859-1"?>
<employee firstName="Brian" lastName="May">
</employee>
Employee.java
public class Employee {
private String firstName;
private String lastName;
private ArrayList offices = new ArrayList();
public Employee() {
System.out.println("Creating Employee");
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
System.out.println("Setting firstName : " + firstName);
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
System.out.println("Setting lastName : " + lastName);
this.lastName = lastName;
}
public void addOffice(Office office) {
System.out.println("Adding Office to this employee");
offices.add(office);
}
public ArrayList getOffices() {
return offices;
}
public void printName() {
System.out.println("My name is " + firstName + " " + lastName);
}
}
Test01.java
public class Test01 {
public static void main(String[] args) {
String path = System.getProperty("user.dir") + File.separator + "etc";
File file = new File(path, "employee1.xml");
Digester digester = new Digester();
// add rules
digester.addObjectCreate("employee", "ex15.pyrmont.digestertest.Employee");
digester.addSetProperties("employee");
digester.addCallMethod("employee", "printName");
try {
Employee employee = (Employee) digester.parse(file);
System.out.println("First name : " + employee.getFirstName());
System.out.println("Last name : " + employee.getLastName());
}
catch(Exception e) {
e.printStackTrace();
}
}
}
结果：
Creating Employee
Setting firstName : Brian
Setting lastName : May
My name is Brian May
First name : Brian
Last name : May
Example 2 :
xml file :
<?xml version="1.0" encoding="ISO-8859-1"?>
<employee firstName="Freddie" lastName="Mercury">
<office description="Headquarters">
<address streetName="Wellington Avenue" streetNumber="223"/>
</office>
<office description="Client site">
<address streetName="Downing Street" streetNumber="10"/>
</office>
</employee>
Office.java
public class Office {
private Address address;
private String description;
public Office() {
System.out.println("..Creating Office");
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
System.out.println("..Setting office description : " + description);
this.description = description;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
System.out.println("..Setting office address : " + address);
this.address = address;
}
}
Address.java
public class Address {
private String streetName;
private String streetNumber;
public Address() {
System.out.println("....Creating Address");
}
public String getStreetName() {
return streetName;
}
public void setStreetName(String streetName) {
System.out.println("....Setting streetName : " + streetName);
this.streetName = streetName;
}
public String getStreetNumber() {
return streetNumber;
}
public void setStreetNumber(String streetNumber) {
System.out.println("....Setting streetNumber : " + streetNumber);
this.streetNumber = streetNumber;
}
public String toString() {
return "...." + streetNumber + " " + streetName;
}
}
Test02.java
public class Test02 {
public static void main(String[] args) {
String path = System.getProperty("user.dir") + File.separator + "etc";
File file = new File(path, "employee2.xml");
Digester digester = new Digester();
// add rules
digester.addObjectCreate("employee", "ex15.pyrmont.digestertest.Employee");
digester.addSetProperties("employee");
digester.addObjectCreate("employee/office", "ex15.pyrmont.digestertest.Office");
digester.addSetProperties("employee/office");
digester.addSetNext("employee/office", "addOffice");
digester.addObjectCreate("employee/office/address",
"ex15.pyrmont.digestertest.Address");
digester.addSetProperties("employee/office/address");
digester.addSetNext("employee/office/address", "setAddress");
try {
Employee employee = (Employee) digester.parse(file);
ArrayList offices = employee.getOffices();
Iterator iterator = offices.iterator();
System.out.println("-------------------------------------------------");
while (iterator.hasNext()) {
Office office = (Office) iterator.next();
Address address = office.getAddress();
System.out.println(office.getDescription());
System.out.println("Address : " +
address.getStreetNumber() + " " + address.getStreetName());
System.out.println("--------------------------------");
}
}
catch(Exception e) {
e.printStackTrace();
}
}
}
运行结果为：
Creating Employee
Setting firstName : Freddie
Setting lastName : Mercury
..Creating Office
..Setting office description : Headquarters
....Creating Address
....Setting streetName : Wellington Avenue
....Setting streetNumber : 223
..Setting office address : ....223 Wellington Avenue
Adding Office to this employee
..Creating Office
..Setting office description : Client site
....Creating Address
....Setting streetName : Downing Street
....Setting streetNumber : 10
..Setting office address : ....10 Downing Street
Adding Office to this employee
-------------------------------------------------
Headquarters
Address : 223 Wellington Avenue
--------------------------------
Client site
Address : 10 Downing Street
--------------------------------
Example 3 :
在给digester注入解析规则的时候，上面的两个例子是逐条注入的。还有一种方法是 集体注入。
实体对象沿用上例中的定义。
规则的集合定义在一个类中
EmployeeRoleSet.java
public class EmployeeRuleSet extends RuleSetBase {
public void addRuleInstances(Digester digester) {
// add rules
digester.addObjectCreate("employee", "ex15.pyrmont.digestertest.Employee");
digester.addSetProperties("employee");
digester.addObjectCreate("employee/office", "ex15.pyrmont.digestertest.Office");
digester.addSetProperties("employee/office");
digester.addSetNext("employee/office", "addOffice");
digester.addObjectCreate("employee/office/address",
"ex15.pyrmont.digestertest.Address");
digester.addSetProperties("employee/office/address");
digester.addSetNext("employee/office/address", "setAddress");
}
}
Test03.java
public class Test03 {
public static void main(String[] args) {
String path = System.getProperty("user.dir") + File.separator + "etc";
File file = new File(path, "employee2.xml");
Digester digester = new Digester();
digester.addRuleSet(new EmployeeRuleSet());//注入规则集合
try {
Employee employee = (Employee) digester.parse(file);
ArrayList offices = employee.getOffices();
Iterator iterator = offices.iterator();
System.out.println("-------------------------------------------------");
while (iterator.hasNext()) {
Office office = (Office) iterator.next();
Address address = office.getAddress();
System.out.println(office.getDescription());
System.out.println("Address : " +
address.getStreetNumber() + " " + address.getStreetName());
System.out.println("--------------------------------");
}
}
catch(Exception e) {
e.printStackTrace();
}
}
}
结果为：
Creating Employee
Setting firstName : Freddie
Setting lastName : Mercury
..Creating Office
..Setting office description : Headquarters
....Creating Address
....Setting streetName : Wellington Avenue
....Setting streetNumber : 223
..Setting office address : ....223 Wellington Avenue
Adding Office to this employee
..Creating Office
..Setting office description : Client site
....Creating Address
....Setting streetName : Downing Street
....Setting streetNumber : 10
..Setting office address : ....10 Downing Street
Adding Office to this employee
-------------------------------------------------
Headquarters
Address : 223 Wellington Avenue
--------------------------------
Client site
Address : 10 Downing Street
--------------------------------
ContextConfig
下面 言归正传 ， 通过讲解contextConfig，来看看tomcat的web.xml文件（两个，tomcat default一个，application一个）是怎么注入到context中的。
（待续...）