1. 通过构造函数实现DI
简单类型实例
package examples;
public class ExampleBean {
// Number of years to calculate the Ultimate Answer
private int years;
// The Answer to Life, the Universe, and Everything
private String ultimateAnswer;
//如果不能在debug模式下进行编译，必须要加下面一行。针对下面的方式3，通过参数名字。
@ConstructorProperties({"years", "ultimateAnswer"})
public ExampleBean(int years, String ultimateAnswer) {
this.years = years;
this.ultimateAnswer = ultimateAnswer;
}
}相应的xml配置为
<bean id="exampleBean" class="examples.ExampleBean"> //方式1，通过类型，如果存在两个参数同类型的话，不行。
<constructor-arg type="int" value="7500000"/>
<constructor-arg type="java.lang.String" value="42"/> //方式2，通过参数位置。
<constructor-arg index="0" value="7500000"/>
<constructor-arg index="1" value="42"/>
//方式3，通过参数名字。
<constructor-arg name="years" value="7500000"/>
<constructor-arg name="ultimateAnswer" value="42"/>
</bean>
对象类型实例
package x.y;
public class Foo {
public Foo(Bar bar, Baz baz) {
// ...
}
}xml配置
<beans>
<bean id="foo" class="x.y.Foo">
<constructor-arg ref="bar"/>
<constructor-arg ref="baz"/>
</bean> <bean id="bar" class="x.y.Bar"/> <bean id="baz" class="x.y.Baz"/>
</beans>
参数也可以像下面这样指定
<constructor-arg>
<ref bean="bar"/>
</constructor-arg>
如果是通过工厂模式，可以采用下面的方式
<bean id="exampleBean" class="examples.ExampleBean" factory-method="createInstance">
<constructor-arg ref="anotherExampleBean"/>
<constructor-arg ref="yetAnotherBean"/>
<constructor-arg value="1"/>
</bean> <bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
public class ExampleBean {
// a private constructor
private ExampleBean(...) {
...
}
// a static factory method; the arguments to this method can be
// considered the dependencies of the bean that is returned,
// regardless of how those arguments are actually used.
public static ExampleBean createInstance (
AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) {
ExampleBean eb = new ExampleBean (...);
// some other operations...
return eb;
}
}2. 通过set方法来实现DI
<bean id="exampleBean" class="examples.ExampleBean">
<!-- setter injection using the nested ref element -->
<property name="beanOne">
<ref bean="anotherExampleBean"/>
</property> <!-- setter injection using the neater ref attribute -->
<property name="beanTwo" ref="yetAnotherBean"/>
<property name="integerProperty" value="1"/>
</bean> <bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
注：property的name是和set方法中的名字一致的。
public class ExampleBean {
private AnotherBean beanOne;
private YetAnotherBean beanTwo;
private int i;
public void setBeanOne(AnotherBean beanOne) {
this.beanOne = beanOne;
}
public void setBeanTwo(YetAnotherBean beanTwo) {
this.beanTwo = beanTwo;
}
public void setIntegerProperty(int i) {
this.i = i;
}
}总结：在我们日常的工程中，上面两种方式如何使用呢？
可以从需要来看，如果这个属性是必须的，那就放在构造函数中；如果是可选的，那就用set的方式好了。