Java如何在Spring中使用set元素注入集合？
在此示例中，您将看到如何使用<set>元素连接bean的collection属性。我们将重用在上一个示例中使用的Bean。如何在Spring中使用list元素注入集合？
该Album豆有一个songs是有一个类型的属性java.util.List。该<set>元素不必与一起使用java.util.Set。它可用于连接java.util.List收藏集。这只是意味着它不能包含重复值，因此集合将仅包含唯一值。
这是我们如何配置Spring上下文：
<?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="song1">
<property name="title" value="I Saw Her Standing There" />
<property name="writer" value="Beatles" />
</bean>
<bean id="song2">
<property name="title" value="Misery" />
<property name="writer" value="Beatles" />
</bean>
<bean id="song3">
<property name="title" value="Anna (Go to Him)" />
<property name="writer" value="Beatles" />
</bean>
<bean id="album">
<property name="title" value="Please Please Me"/>
<property name="year" value="1963"/>
<property name="songs">
<set>
<ref bean="song1"/>
<ref bean="song1"/>
<ref bean="song1"/>
</set>
</property>
</bean>
</beans>该<set>配置可以在albumbean配置中看到。我们设置songs属性。在这个property元素中，我们使用<set>元素。然后使用<ref>元素将一些bean添加到集合中。
创建以下代码以运行它：
package org.nhooo.example.spring.collection;
public class Song {
private String title;
private String writer;
public Song() {
}
public void setTitle(String title) {
this.title = title;
}
public void setWriter(String writer) {
this.writer = writer;
}
@Override
public String toString() {
return "Song{" +
"title='" + title + '\'' +
", writer='" + writer + '\'' +
'}';
}
}package org.nhooo.example.spring.collection;
public class Publisher {
private String name;
public Publisher() {
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Publisher{" +
"name=" + name +
'}';
}
}package org.nhooo.example.spring.collection;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;
public class Album {
private String title;
private int year;
private List<Song> songs = new ArrayList<>();
private Map<String, Publisher> publisher = new HashMap<>();
private Properties props = new Properties();
public Album() {
}
public void setTitle(String title) {
this.title = title;
}
public void setYear(int year) {
this.year = year;
}
public void setSongs(List<Song> songs) {
this.songs = songs;
}
public void setPublisher(Map<String, Publisher> publisher) {
this.publisher = publisher;
}
public void setProps(Properties props) {
this.props = props;
}
@Override
public String toString() {
return "Album{" +
"title='" + title + '\'' +
", year=" + year +
", songs=" + songs +
", publisher=" + publisher +
", props=" + props +
'}';
}
}package org.nhooo.example.spring.collection;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class DemoSet {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext(
new String[]{"collection-set.xml"});
Album album = (Album) context.getBean("album");
System.out.println("Album = " + album);
}
}您将在屏幕上看到以下输出。如您所见，尽管我们在songs属性中设置了三个bean，但该Albumbean只包含一首歌曲。这是因为我们使用<set>元素来连接集合。它不允许重复值。
Album = Album{title='Please Please Me', year=1963, songs=[Song{title='I Saw Her Standing There', writer='Beatles'}], publisher={}, props={}}