Resource(3)

ResourceLoader

ResourceLoader接口返回的是一个Resource 对象

Spring提供了两个ResourceLoader接口的实现
- DefaultResourceLoader
适用于所有环境，可以返回UrlResource，ClassPathResource
- ServletContextResourceLoader
适用于web环境，拥有DefaultResourceLoader的功能，另外还额外提供了获取ServletContextResource的支持

ResourceLoader在进行资源加载时需要使用前缀来指定，需要加载“classpath：path”则返回ClassPathResouce，“http://path”和”file:path”则返回UrlResource，如果没有加载则需要根据上下文判断，DefaultResourceLoader默认是加载classpath

ResourceLoader.class

package org.springframework.core.io;public abstract interface ResourceLoader{  public static final String CLASSPATH_URL_PREFIX = "classpath:";  public abstract Resource getResource(String paramString);  public abstract ClassLoader getClassLoader();}

DefaultResourceLoader.class

  public Resource getResource(String location)  {    Assert.notNull(location, "Location must not be null");    if (location.startsWith("classpath:")) {      return new ClassPathResource(location.substring("classpath:".length()), getClassLoader());    }    try    {      URL url = new URL(location);      return new UrlResource(url);    }    catch (MalformedURLException ex) {    }    return getResourceByPath(location);  }

ResourceLoaderTest.java

package com.test;import java.net.MalformedURLException;import org.junit.Test;import org.springframework.core.io.DefaultResourceLoader;import org.springframework.core.io.Resource;import org.springframework.core.io.ResourceLoader;import org.springframework.core.io.UrlResource;public class ResourceLoaderTest {@Testpublic void ResourceLoaderTest(){    ResourceLoader loader=new DefaultResourceLoader();    Resource resource;    //加载UrlResource    resource = loader.getResource("file:d:\\a.txt");//startwith file:    if(resource.exists()){        ResourceUtil.stream(resource);          }    resource=loader.getResource("http://www.baidu.com");//startwith http://    if(resource.exists()){        ResourceUtil.stream(resource);          }     //加载ClassPathResource    resource = loader.getResource("classpath:test.properties");//startwith classpath:    if(resource.exists()){        ResourceUtil.stream(resource);          }    //默认加载ClassPathResource    resource = loader.getResource("test.properties");    if(resource.exists()){        ResourceUtil.stream(resource);          } }}

ApplicationContext都实现了ResourceLoader接口

• ClassPathXmlApplicationContext:不指定前缀则返回ClassPathResource,否则根据前缀来返回Resource
• FileSystemXmlApplicationContext：不指定前缀则返回FileSystemResource,否则根据前缀来返回Resource
• WebApplicationContext：不指定前缀则返回ServletContextResource,否则根据前缀来返回Resource
• 其他：根据当前上下文来返回Resource，,否则根据前缀来返回Resource

ApplicationContextResourceTest .java

package com.test;import org.junit.Test;import org.springframework.context.support.ClassPathXmlApplicationContext;import org.springframework.core.io.Resource;public class ApplicationContextResourceTest {@Testpublic void ApplicationContextResourceTest(){    ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext();    //默认返回ClassPathResouce    Resource resource=context.getResource("applicationContextParent.xml");    if(resource.exists()){        ResourceUtil.stream(resource);          }     //根据前缀返回UrlResource    Resource resource=c2.getResource("http://www.baidu.com");    if(resource.exists()){        ResourceUtil.stream(resource);          } }}

ResourceLoaderAware(回调ResourceLoader)

ResourceLoaderAware是一个标记接口，通过ApplicationContext上下文注入ResourceLoader

定义一个Bean实现ResourceLoaderAware接口

ResourceBean .java

package com.resource;import org.springframework.context.ResourceLoaderAware;import org.springframework.core.io.ResourceLoader;public class ResourceBean implements ResourceLoaderAware{    private ResourceLoader loader;    @Override    public void setResourceLoader(ResourceLoader loader) {     this.loader= loader;           }    public ResourceLoader getLoader() {        return loader;    }}

简单配置Bean

       <bean id="resourceBean" class="com.resource.ResourceBean">               </bean>

测试类
ResourceLoaderAwareTest .java

package com.test;import org.junit.Assert;import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import org.springframework.core.io.ResourceLoader;import com.resource.ResourceBean;public class ResourceLoaderAwareTest {    @Testpublic void ResourceLoaderAwareTest(){        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContextResource.xml");        ResourceBean resourceBean=context.getBean("resourceBean",ResourceBean.class);        ResourceLoader loader=resourceBean.getLoader();        //ApplicationContext是一个ResourceLoader        Assert.assertTrue(loader instanceof ApplicationContext);    }}

注入Resource

回调或者注入ResourceLoader，然后在通过ResourceLoader来加载需要的资源，是否对只需要加载固定资源的时候，显得麻烦。
Spring提供了一个PropertyEditor“ResourceEditor”用于在注入的字符串和Resource之间进行转换。因此可以使用注入方式注入Resource。
ResourceEditor使用ApplicationContext注入的路径字符串获取相应的Resource。

定义一个Bean

ResourceBean .java

package com.resource;import org.springframework.core.io.Resource;public class ResourceBean {    private Resource resource;    public Resource getResource() {        return resource;    }    public void setResource(Resource resource) {        this.resource = resource;    }}

配置文件

       <bean id="resourceBean1" class="com.resource.ResourceBean">       <property name="resource" value="applicationContextResource.xml"/>               </bean>       <bean id="resourceBean2" class="com.resource.ResourceBean">       <property name="resource" value="classpath:applicationContextResource.xml"/>               </bean>

注意此处“resourceBean1”没有指定前缀所以根据使用的ApplicationContext的实现（ClassPathXmlApplicationContext、FileSystemXmlApplicationContext、WebApplicationContext等）来选着Resource的实现

测试类
ResourceTest .java

package com.test;import org.junit.Assert;import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import org.springframework.core.io.ClassPathResource;import com.resource.ResourceBean;public class ResourceTest {    @Testpublic void ResourceTest(){        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContextResource.xml");        ResourceBean resourceBean1=context.getBean("resourceBean1",ResourceBean.class);        ResourceBean resourceBean2=context.getBean("resourceBean2",ResourceBean.class);        if(resourceBean1.getResource().exists()){            ResourceUtil.stream(resourceBean1.getResource());               }        Assert.assertTrue(resourceBean1.getResource() instanceof ClassPathResource);        Assert.assertTrue(resourceBean2.getResource() instanceof ClassPathResource);    }}