Spring-IOC MethodInvokingFactoryBean 类源码解析
MethodInvokingFactoryBean
MethodInvokingFactoryBean的作用是，通过定义类和它的方法，然后生成的bean是这个方法的返回值，即可以注入方法返回值。
MethodInvokingFactoryBean用来获得某个方法的返回值，该方法既可以是静态方法，也可以是实例方法。
该方法的返回值可以注入bean实例属性，也可以直接定义成bean实例。
静态方法返回值注入
配置：
方式1:直接注入staticMethod属性，写明类的全限定名加方法名：
<bean id="myObject" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="staticMethod" value="com.whatever.MyClassFactory.getInstance"/>
</bean>
Spring会将此属性切分为class和method，就和方式2的配置结果一样。具体源码如下：
public void prepare() throws ClassNotFoundException, NoSuchMethodException {
// 此属性不为空，进行拆分
if (this.staticMethod != null) {
int lastDotIndex = this.staticMethod.lastIndexOf('.');
if (lastDotIndex == -1 || lastDotIndex == this.staticMethod.length()) {
throw new IllegalArgumentException(
"staticMethod must be a fully qualified class plus method name: " +
"e.g. 'example.MyExampleClass.myExampleMethod'");
}
String className = this.staticMethod.substring(0, lastDotIndex);
String methodName = this.staticMethod.substring(lastDotIndex + 1);
this.targetClass = resolveClassName(className);
this.targetMethod = methodName;
}
Class<?> targetClass = getTargetClass();
String targetMethod = getTargetMethod();
Assert.notNull(targetClass, "Either 'targetClass' or 'targetObject' is required");
Assert.notNull(targetMethod, "Property 'targetMethod' is required");
Object[] arguments = getArguments();
Class<?>[] argTypes = new Class<?>[arguments.length];
for (int i = 0; i < arguments.length; ++i) {
argTypes[i] = (arguments[i] != null ? arguments[i].getClass() : Object.class);
}
// Try to get the exact method first.
try {
this.methodObject = targetClass.getMethod(targetMethod, argTypes);
}
catch (NoSuchMethodException ex) {
// Just rethrow exception if we can't get any match.
this.methodObject = findMatchingMethod();
if (this.methodObject == null) {
throw ex;
}
}
}
方式二
<bean id="sysProps" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetClass" value="java.lang.System"/>
<property name="targetMethod" value="getProperties"/>
</bean>
增加参数
<bean id="javaVersion" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetObject" ref="sysProps"/>
<property name="targetMethod" value="getProperty"/>
<property name="arguments" value="java.version"/>
</bean>
应用 -- 初始化Spring容器时，将某些配置注入到环境变量中
<bean id="sysProps" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetClass" value="java.lang.System"/>
<property name="targetMethod" value="getProperties"/>
</bean>
<bean id="javaVersion" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetObject" ref="sysProps"/>
<property name="targetMethod" value="putAll"/>
<property name="arguments">
<props>
<prop key="kafka.consumer.host">10.10.10.48:9092</prop>
</props>
</property>
</bean>
