显示目录

Setter 注入

CommonUtils

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package com.xtuer.util;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.util.DefaultIndenter;
import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
import com.fasterxml.jackson.databind.ObjectMapper;
public class CommonUtils {
private static DefaultPrettyPrinter printer;
static {
// Setup a pretty printer with an indenter (indenter has 4 spaces in this case)
DefaultPrettyPrinter.Indenter indenter = new DefaultIndenter(" ", DefaultIndenter.SYS_LF);
printer = new DefaultPrettyPrinter();
printer.indentObjectsWith(indenter);
printer.indentArraysWith(indenter);
}
/**
* 以 Json 的格式输出对象
* @param obj
*/
public static void output(Object obj) {
ObjectMapper mapper = new ObjectMapper();
try {
// 默认用 2 个空格缩进
// System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj));
// 自定义缩进,用 4 个空格
System.out.println(mapper.writer(printer).writeValueAsString(obj));
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}

User

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package com.xtuer.beans;
public class User {
private int id;
private String username;
private String password;
private Address address;
// 省略 setter and getter
}

Address

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package com.xtuer.beans;
public class Address {
private int id;
private String country;
private String province;
private String street;
// 省略 setter and getter
}

spring-beans.xml

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<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="address" class="com.xtuer.beans.Address">
<property name="country" value="China"/>
<property name="province" value="BeiJing"/>
<property name="street" value="ChaoYang"/>
</bean>
<bean id="user" class="com.xtuer.beans.User">
<property name="username" value="Alice"/>
<property name="password" value="Passw0rd"/>
<property name="address" ref="address"/>
</bean>
</beans>

InjectionTest

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import com.xtuer.beans.User;
import com.xtuer.util.CommonUtils;
import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class InjectionTest {
private static ApplicationContext context;
@BeforeClass
public static void setup() {
context = new ClassPathXmlApplicationContext("spring-beans.xml");
}
@Test
public void test() {
User user = context.getBean("user", User.class);
CommonUtils.output(user);
}
}

输出

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{
"id" : 0,
"username" : "Alice",
"password" : "Passw0rd",
"address" : {
"id" : 0,
"country" : "China",
"province" : "BeiJing",
"street" : "ChaoYang"
}
}

说明

  1. <property name="username" value="Alice"/> 调用 user.setUsername(“Alice”) 设置属性 username。
  2. <property name="address" ref="address"/>,找到标志为 address(可以是 id, name, alias) 的 Bean,然后调用 user.setAddress(address) 设置属性 address。

注入方式: attribute 和 element

  • value 和 ref 都可以使用 attribute 和 element 的方式注入,推荐尽量用 attribute 的方式,这样会简洁一些
  • value 用于简单类型: primitive type(int, boolean, float 等), String, Date, 还有注册了 PropertyEditor 的类型(把字符串转换成对象)。
  • ref 用于引用 Bean Configuration File 里定义的另一个 Bean

value 用 element 的方式如下注入:

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<bean id="user" class="com.xtuer.beans.User">
<property name="username">
<value>Alice</value>
</property>
<property name="password" value="Passw0rd"/>
<property name="address" ref="address"/>
</bean>

ref 用 element 的方式如下注入:

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<bean id="user" class="com.xtuer.beans.User">
<property name="username" value="Alice"/>
<property name="password" value="Passw0rd"/>
<property name="address">
<ref bean="address"/>
</property>
</bean>

注入匿名对象

每创建一次 User,都会新创建一个 Address 的匿名对象。
使用 <bean>,不能设置 id, name 等。

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<bean id="user" class="com.xtuer.beans.User">
<property name="username" value="Alice"/>
<property name="password" value="Passw0rd"/>
<property name="address">
<bean class="com.xtuer.beans.Address">
<property name="country" value="Germany"/>
<property name="province" value="Braunschweig"/>
<property name="street" value="Wiesenstrasse"/>
</bean>
</property>
</bean>