依賴注入的兩種形式

1.1構造方法注入

LowerAction.class

public class LowerAction implements Action {
    private String prefix;
    private String message;

    public  LowerAction(){}

    public  LowerAction(String prefix, String message){
        this.prefix = prefix;
        this.message = message;
    }
    public String getPrefix() {
        return prefix;
    }
    public String getMessage() {
        return message;
    }
    public void setPrefix(String string) {
        prefix = string;
    }
    public void setMessage(String string) {
        message = string;
    }
    public void execute(String str) {
        System.out.println((getPrefix() + ", " + getMessage() + ", " + str).toLowerCase());
    }
}

ApplicationContext.xml中的TheAction2的Bean

    <bean id="TheAction2" class="com.example.service.LowerAction">
        <constructor-arg index="0">
            <value>Hi</value>
        </constructor-arg>
        <constructor-arg index="1">
            <value>Good Afternoon</value>
        </constructor-arg>
    </bean>

測試函數

    @Test
    public void test5() {
        String XML = "file:src/applicationContext.xml";
        ApplicationContext ctx = new ClassPathXmlApplicationContext(XML);

        LowerAction lowerAction=(LowerAction) ctx.getBean("TheAction2");
        System.out.println(lowerAction.getPrefix());
        System.out.println(lowerAction.getMessage());

    }

測試結果

測試結果

實驗中想到的問題：構造注入只能通過index索引匹配嗎？
還有類型匹配

<bean id="TheAction4" class="com.example.service.LowerAction">
        <constructor-arg type="java.lang.String">
            <value>Hi</value>
        </constructor-arg>
        <constructor-arg type="java.lang.String">
            <value>Wushuohan</value>
        </constructor-arg>
    </bean>

以及參數名傳值

<bean id="TheAction6" class="com.example.service.LowerAction">
        <constructor-arg name="prefix" value="Hi">
        </constructor-arg>
        <constructor-arg type="message" value="Wushuohan">
        </constructor-arg>
    </bean>

測試結果如下

測試結果

Setter()方法注入

ApplicationContext.xml中的TheAction1的Bean

<bean id="TheAction1" class="com.example.service.LowerAction">
        <property name="prefix">
            <value>Hi</value>
        </property>
        <property name="message">
            <value>Good Morning</value>
        </property>
    </bean>

測試函數

    @Test
    public void test4() {
        String XML = "file:src/applicationContext.xml";
        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext(XML);
        LowerAction lowerAction=(LowerAction) ctx.getBean("TheAction1");
        System.out.println(lowerAction.getPrefix());
        System.out.println(lowerAction.getMessage());
    }

測試結果如下

測試結果

實驗中想到的問題：Setter()注入能不能沒有構造函數？
注釋掉LowerAction的構造函數

public class LowerAction implements Action {
    private String prefix;
    private String message;

    public void execute(String str) {
        System.out.println((getPrefix() + ", " + getMessage() + ", " + str).toLowerCase());
    }
}

運行后報錯

報錯

TheAction2沒有了構造函數

運行成功

本章總結

對于依賴關系無需變化的注入，盡量采用構造注入。而其他的依賴關系的注入，則考慮采用設值注入。