Spring IOC 建立bean例項的方式
阿新 • • 發佈：2018-12-31
據我所知，建立bean例項的方式有4種方式~
下面我會一一寫出來這4種方式~
第一種：xml檔案中有bean的配置,而且這個bean所對應的java類中存在一個無參構造器，那麼這個時候spring容器就可以使用反射呼叫無參構造器來建立例項了~
程式碼如下：
這就是一個bean例項~，我前幾篇就是這樣建立bean例項的，我這裡就不多說了~接下來看第二種方式<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd"> <bean name="stu" class="com.x.spring.test1.Student"> <property name="name"> <value>張三</value> </property> </bean> </beans>
第二種：通過工廠類獲得例項(工廠類實現了介面FactoryBean<?>)
注意：spring中的PropertyPlaceholderConfigurer類的使用,在htmlsingle中直接搜尋類名即可
例如:
工廠類ConnectionFactory實現指定介面並且實現介面中的三個抽象方法:
注意：一定要加上這個jar包-mysql-connector-java-5.1.18-bin.jar，這個jar包我在Hibernate裡面就用過，這是連線資料庫的~如圖：public class ConnectionFactory implements FactoryBean<Connection>{ private String driver; private String url; private String username; private String password; public String getDriver() { return driver; } public void setDriver(String driver) { this.driver = driver; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } //連線 @Override public Connection getObject() throws Exception { Class.forName(driver); Connection conn = DriverManager.getConnection(url,username,password); return conn; } @Override public boolean isSingleton() { // TODO Auto-generated method stub return false; } @Override public Class<Connection> getObjectType() { // TODO Auto-generated method stub return Connection.class; } }
配置檔案factory.xml:
還需要properties檔案~我放在src目錄下面~<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <!-- 通過conn拿到的是對應的這個工廠類所生產的產品物件 --> <!-- 造成這種現象的原因:因為這個類ConnectionFactory是一個工廠類,所以我們用名字conn在容器中拿物件的時候, 拿到並不是這個工廠類物件,而是這個工廠類物件呼叫完工廠方法後所返回的物件. --> <bean name="conn" class="com.x.spring.test3.factory.ConnectionFactory"> <!-- 從一個配置檔案中以key—value的形式拿value --> <property name="url" value="${url}"></property> <property name="driver" value="${driver}"></property> <property name="username" value="${username}"></property> <property name="password" value="${password}"></property> </bean> <!-- 下面配置的這個類,可以自動的幫我們去讀取指定的properties檔案的 內容,檔案中用key-value的形式存放資料,讀完之後我們就可以用 ${key}這種形式去拿檔案中的value值了。 classpath指的是從src下面找. --> <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations" value="classpath:mysql.properties"/> </bean> </beans>
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/ssh
username=root
password=rootpublic class FactoryTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
//在xml中配置工廠類，然後通過這個工廠類獲得工廠生產的例項
try {
String path = "com/x/spring/test3/factory/factory.xml";
ApplicationContext container =
new ClassPathXmlApplicationContext(path);
Connection conn = (Connection)container.getBean("conn");
System.out.println(conn);
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
注意： 通過conn拿到的並不是要拿到工廠類的物件，而是對應的這個工廠類所生產的產品物件~這一點要記住
好了，第二種方式寫完了，開始第三種方式~
第三種：通過例項工廠獲得例項(不需要實現或者繼承任何介面或者父類)
注意spring中的PropertyPlaceholderConfigurer類的使用,在htmlsingle中直接搜尋類名即可
例如：
一個普通的工程類ConnectionFactory：
public class ConnectionFactory {
private String driver;
private String url;
private String username;
private String password;
public Object getConnection() throws Exception {
Class.forName(driver);
Connection conn =
DriverManager.getConnection(url,username,password);
return conn;
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
配置檔案instanceFactory.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd">
<span style="color:#ff0000;"><!-- 讀取properties檔案 --></span>
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations" value="classpath:mysql.properties"/>
</bean>
<bean name="factory" class="com.x.spring.test3.instanceFactory.ConnectionFactory">
<property name="url" value="${url}"></property>
<property name="driver" value="${driver}"></property>
<property name="username" value="${username}"></property>
<property name="password" value="${password}"></property>
</bean>
<span style="color:#ff0000;"> <!--
將來通過這個conn來拿物件,拿到的是名字為factory的工廠類呼叫完
名字為getConnection方法之後所返回的物件。
--></span>
<bean name="conn" factory-bean="factory" factory-method="getConnection"></bean>
</beans>測試類InstanceTest:
public class InstanceTest {
public static void main(String[] args) {
//通過例項工廠獲得例項(不需要實現或者繼承任何介面或者父類)
try {
String path = "com/x/spring/test3/instanceFactory/instanceFactory.xml";
ApplicationContext container =
new ClassPathXmlApplicationContext(path);
Connection conn = (Connection)container.getBean("conn");
System.out.println(conn);
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
效果圖：
好了，第三種方式也說完了~接下來第四種~
第四種：通過靜態工廠獲得例項
例如:含義靜態方法的工廠類ConnectionFactory
public class ConnectionFactory {
private static String driver = "com.mysql.jdbc.Driver";
private static String url = "jdbc:mysql://localhost:3306/ssh";
private static String username = "root";
private static String password = "root";
public static Object getConnection() throws Exception {
Class.forName(driver);
Connection conn =
DriverManager.getConnection(url,username,password);
return conn;
}
}這就可以不用寫properties檔案了~
配置檔案staticFactory.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd">
<!-- 這樣配置一定要求getConnection方法是靜態方法 -->
<bean name="conn" class="com.x.spring.test3.staticFactory.ConnectionFactory" factory-method="getConnection"></bean>
</beans>public class StaticTest {
public static void main(String[] args) {
//通過靜態工廠獲得例項
try {
String path = "com/x/spring/test3/staticFactory/staticFactory.xml";
ApplicationContext container =
new ClassPathXmlApplicationContext(path);
Connection conn = (Connection)container.getBean("conn");
System.out.println(conn);
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
執行效果：
有沒有覺得這三種方式的效果圖都差不多~
就後面的一些數字不一樣~
看來這三種方式通過conn拿到的並不是要拿到工廠類的物件，而是對應的這個工廠類所生產的產品物件~這一點要記住