Changes between Version 25 and Version 26 of waue/2011/spring

Timestamp:

Aug 26, 2011, 5:27:17 PM (13 years ago)

Author:

waue

Comment:

--

waue/2011/spring

@@ -535 +535 @@
 
 
-
-
-
+ == bean 給值的前後設定 ==
+
+在Bean的屬性被Spring容器設定之後，您還有機會自訂一些對Bean的修正，您可以實作org.springframework.beans.factory.config.BeanPostProcessor介面：
+
+{{{
+#!java
+package org.springframework.beans.factory.config;
+public interface BeanPostProcessor {
+    public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException;
+    public Object postProcessAfterInitialization(Object bean, String name) throws BeansException;
+}
+}}}
+
+postProcessBeforeInitialization()方法會在Bean初始化動作之前（例如InitializingBean的 afterPropertiesSet()方法或自定義的init方法）被呼叫，而postProcessAfterInitialization()方法會在Bean初始化之後立即被呼叫。
+
+舉個例子來說，您可以實作一個大寫修正器，對於String型態的Bean屬性，無論在定義檔中是設定為大寫或小寫，在Bean屬性設定之後，您可以在大寫修正器中將所有的String改為大寫，例如：
+
+ * UpperCaseModifier.java
+
+{{{
+#!java
+package onlyfun.caterpillar;
+
+import java.lang.reflect.Field;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+
+public class UpperCaseModifier implements BeanPostProcessor {
+
+    public Object postProcessBeforeInitialization(
+                        Object bean, String name) throws BeansException {
+        Field[] fields = bean.getClass().getDeclaredFields();
+        
+        for(int i = 0; i < fields.length; i++) {
+            if(fields[i].getType().equals(String.class)) {
+                fields[i].setAccessible(true);
+                try {
+                    String original = (String) fields[i].get(bean);
+                    fields[i].set(bean, original.toUpperCase());
+                } catch (IllegalArgumentException e) {
+                    e.printStackTrace();
+                } catch (IllegalAccessException e) {
+                    e.printStackTrace();
+                }
+            }
+        }
+        
+        return bean;
+    }
+
+    public Object postProcessAfterInitialization(
+                          Object bean, String name) throws BeansException {
+        return bean;
+    }
+
+}
+}}}
+
+假設您定義了這麼一個Bean類別：
+
+ * HelloBean.java
+
+{{{
+#!java
+package onlyfun.caterpillar; 
+
+public class HelloBean { 
+    private String helloWord; 
+    
+    public HelloBean() {
+    }
+    
+    public void setHelloWord(String helloWord) { 
+        this.helloWord = helloWord; 
+    } 
+    public String getHelloWord() { 
+        return helloWord; 
+    } 
+}
+}}}
+
+ApplicationContext會自動偵測您是否在定義檔中定義了實作BeanPostProcessor介面的類別，例如：
+
+ * beans-config.xml
+
+{{{
+#!java
+<?xml version="1.0" encoding="UTF-8"?> 
+<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN" 
+  "http://www.springframework.org/dtd/spring-beans.dtd"> 
+
+<beans>  
+    <bean id="upperCaseModifier" 
+          class="onlyfun.caterpillar.UpperCaseModifier"/>
+    
+    <bean id="helloBean" class="onlyfun.caterpillar.HelloBean"> 
+        <property name="helloWord"> 
+            <value>Hello!</value> 
+        </property> 
+    </bean>
+</beans>
+}}}
+
+Spring容器會在每一個Bean被初始化之前之後分別呼叫upperCaseModifier的 postProcessBeforeInitialization()方法與postProcessAfterInitialization()方法，以對Bean進行指定的相關修正，可以實際來看看以下的測試程式：
+
+ * SpringDemo.java
+
+{{{
+#!java
+package onlyfun.caterpillar; 
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.FileSystemXmlApplicationContext; 
+
+public class SpringDemo { 
+    public static void main(String[] args) { 
+        ApplicationContext context = 
+            new FileSystemXmlApplicationContext("beans-config.xml");
+         
+        HelloBean hello = 
+            (HelloBean) context.getBean("helloBean");
+        System.out.println(hello.getHelloWord());
+    } 
+}
+}}}
+
+執行結果如下：
+{{{
+HELLO!
+}}}
+雖然您在定義檔中的helloBean之helloWord屬性是設定小寫字母，但upperCaseModifier將之改為大寫字母了。