满目山河空念远，落花风雨更伤春。
概述
本章学习使用<util：constant>标签将某些Spring bean final静态常量字段注入另外bean。
Spring util：constant示例
从逻辑上讲，你将按照下面给出的方式执行bean。它有两个静态的final字段。MANAGER 和 DIRECTOR。
public class EmployeeDTO
{
public static final EmployeeDTO MANAGER = new EmployeeDTO("manager");
public static final EmployeeDTO DIRECTOR = new EmployeeDTO("director");
private Integer id;
private String firstName;
private String lastName;
private String designation;
public EmployeeDTO(String designation)
{
this.id = -1;
this.firstName = "dummy";
this.lastName = "dummy";
this.designation = designation;
}
//Setters and Getters
@Override
public String toString() {
return "Employee [id=" + id + ", firstName=" + firstName
+ ", lastName=" + lastName + ", type=" + designation + "]";
}
}
您想在EmployeeTypeWrapper类中使用上述字段，如下所示：
<util:constant id="MANAGER"
static-field="cn.howtodoinjava.demo.model.EmployeeDTO.MANAGER" />
<util:constant id="DIRECTOR"
static-field="cn.howtodoinjava.demo.model.EmployeeDTO.DIRECTOR" />
<!-- Use the static final bean constants here -->
<bean name="employeeTypeWrapper" class="cn.howtodoinjava.demo.factory.EmployeeTypeWrapper">
<property name="manager" ref="MANAGER" />
<property name="director" ref="DIRECTOR" />
</bean>
EmployeeTypeWrapper代码如下：
public class EmployeeTypeWrapper {
private EmployeeDTO manager = null;
private EmployeeDTO director = null;
public EmployeeDTO getManager() {
return manager;
}
public void setManager(EmployeeDTO manager) {
this.manager = manager;
}
public EmployeeDTO getDirector() {
return director;
}
public void setDirector(EmployeeDTO director) {
this.director = director;
}
}
测试
测试上面的配置
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
EmployeeTypeWrapper employeeTypeWrapper = (EmployeeTypeWrapper) context.getBean("employeeTypeWrapper");
System.out.println(employeeTypeWrapper.getManager());
System.out.println(employeeTypeWrapper.getDirector());
输出：
Employee [id=-1, firstName=dummy, lastName=dummy, type=manager]
Employee [id=-1, firstName=dummy, lastName=dummy, type=director]
当然，你可以直接在代码中使用字段引用，因为它们是静态字段。但是通过配置文件中定义它们使你可以在任何时候将实现从
MANAGER更改为DIRECTOR，而无需编译源代码。
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原文链接：Spring util:constant to refer final static field references