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...）