一 点睛
Spring EL-Spring表达式语言,支持在xml和注解上使用表达式,类似JSP的EL表达式语言。
Spring开发中经常涉及调用各种资源的情况,包含普通文件、网址、配置文件、系统环境变量等,我们可以使用Spring表达式语言实现资源的注入。
Spring主要在注解@Value的参数中使用表达式。
二 实战
演示Spring EL在以下几种情况下使用:
- 注入普通字符
- 注入操作系统属性
- 注入表达式运算结果
- 注入其他Bean的属性
- 注入文件内容
- 注入网址内容
- 注入属性文件
1 准备,增加commons-io依赖,该依赖可简化文件相关操作,使用commons-io将file转换成字符串
<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.3</version>
</dependency>
2 准备test.txt文件,内容如下
test file
3 准备test.properties,内容如下
book.author=wangyunfei
book.name=spring boot
4 编写需要注入的Bean
package com.wisely.highlight_spring4.ch2.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;
@Service
public class DemoService {
@Value("other class property") //注入普通字符串
private String another;
public String getAnother() {
return another;
}
public void setAnother(String another) {
this.another = another;
}
}
5 编写配置类
package com.wisely.highlight_spring4.ch2.el;
import org.apache.commons.io.IOUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.core.env.Environment;
import org.springframework.core.io.Resource;
@Configuration
@ComponentScan("com.wisely.highlight_spring4.ch2.el")
//注入配置文件需要使用@PropertySource指定文件地址
@PropertySource("classpath:com/wisely/highlight_spring4/ch2/el/test.properties")
public class ElConfig {
@Value("I Love You!") //注入普通字符串
private String normal;
@Value("#{systemProperties['os.name']}") //注入操作系统属性
private String osName;
@Value("#{ T(java.lang.Math).random() * 100.0 }") //注入表达式结果
private double randomNumber;
@Value("#{demoService.another}") //注入其他Bean的属性
private String fromAnother;
@Value("classpath:com/wisely/highlight_spring4/ch2/el/test.txt") //注入文件资源
private Resource testFile;
@Value("http://www.baidu.com") //注入网址资源
private Resource testUrl;
@Value("${book.name}") //注入配置文件属性
private String bookName;
@Autowired
private Environment environment; //注入配置文件还可从environment中获得
//若使用@Value注入,则要配置一个PropertySourcesPlaceholderConfigurer的Bean
@Bean
public static PropertySourcesPlaceholderConfigurer propertyConfigure() {
return new PropertySourcesPlaceholderConfigurer();
}
public void outputResource() {
try {
System.out.println(normal);
System.out.println(osName);
System.out.println(randomNumber);
System.out.println(fromAnother);
System.out.println(IOUtils.toString(testFile.getInputStream()));
System.out.println(IOUtils.toString(testUrl.getInputStream()));
System.out.println(bookName);
System.out.println(environment.getProperty("book.author"));
} catch (Exception e) {
e.printStackTrace();
}
}
}
6 编写主类
package com.wisely.highlight_spring4.ch2.el;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(ElConfig.class);
ElConfig resourceService = context.getBean(ElConfig.class);
resourceService.outputResource();
context.close();
}
}
三 测试
I Love You!
Windows 10
42.94296812896331
other class property
test file
<!DOCTYPE html>
<!--STATUS OK--><html> <head><meta http-equiv=content-type content=text/html;charset=utf-8><meta http-equiv=X-UA-Compatible content=IE=Edge><meta content=always name=referrer><link rel=stylesheet type=text/css href=http://s1.bdstatic.com/r/www/cache/bdorz/baidu.min.css><title>鐧惧害涓?涓嬶紝浣犲氨鐭ラ亾</title></head> <body link=#0000cc> <div id=wrapper> <div id=head> <div class=head_wrapper> <div class=s_form> <div class=s_form_wrapper> <div id=lg> <img hidefocus=true src=//www.baidu.com/img/bd_logo1.png width=270 height=129> </div> <form id=form name=f action=//www.baidu.com/s class=fm> <input type=hidden name=bdorz_come value=1> <input type=hidden name=ie value=utf-8> <input type=hidden name=f value=8> <input type=hidden name=rsv_bp value=1> <input type=hidden name=rsv_idx value=1> <input type=hidden name=tn value=baidu><span class="bg s_ipt_wr"><input id=kw name=wd class=s_ipt value maxlength=255 autocomplete=off autofocus></span><span class="bg s_btn_wr"><input type=submit id=su value=鐧惧害涓?涓? class="bg s_btn"></span> </form> </div> </div> <div id=u1> <a href=http://news.baidu.com name=tj_trnews class=mnav>鏂伴椈</a> <a href=http://www.hao123.com name=tj_trhao123 class=mnav>hao123</a> <a href=http://map.baidu.com name=tj_trmap class=mnav>鍦板浘</a> <a href=http://v.baidu.com name=tj_trvideo class=mnav>瑙嗛</a> <a href=http://tieba.baidu.com name=tj_trtieba class=mnav>璐村惂</a> <noscript> <a href=http://www.baidu.com/bdorz/login.gif?login&;tpl=mn&u=http%3A%2F%2Fwww.baidu.com%2f%3fbdorz_come%3d1 name=tj_login class=lb>鐧诲綍</a> </noscript> <script>document.write('<a href="http://www.baidu.com/bdorz/login.gif?login&tpl=mn&u='+ encodeURIComponent(window.location.href+ (window.location.search === "" ? "?" : "&")+ "bdorz_come=1")+ '" name="tj_login" class="lb">鐧诲綍</a>');</script> <a href=//www.baidu.com/more/ name=tj_briicon class=bri style="display: block;">鏇村浜у搧</a> </div> </div> </div> <div id=ftCon> <div id=ftConw> <p id=lh> <a href=http://home.baidu.com>鍏充簬鐧惧害</a> <a href=http://ir.baidu.com>About Baidu</a> </p> <p id=cp>©2017 Baidu <a href=http://www.baidu.com/duty/>浣跨敤鐧惧害鍓嶅繀璇?</a> <a href=http://jianyi.baidu.com/ class=cp-feedback>鎰忚鍙嶉</a> 浜琁CP璇?030173鍙? <img src=//www.baidu.com/img/gs.gif> </p> </div> </div> </div> </body> </html>
spring boot
wangyunfei