Spring series 8: Reading files in Spring -ResourceLoaderAware

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An overview of the

This article looks at different implementations of resources or files (such as text files, XML files, properties files, or image files) loaded into the context of a Spring application. Spring ResourceLoader provides a unified getResource() method to retrieve external resources through the resource path.

Resources (Resource) interface

Resource is a generic interface in Spring for representing external resources.

Spring provides the following six implementations for the Resource interface.

1. UrlResource
2. ClassPathResource
3. FileSystemResource
4. ServletContextResource
5. InputStreamResource
6. ByteArrayResource

We can specify different prefixes to create paths to load resources from different locations

ResourceLoader

It is used to load resources (such as classpath or file system resources). It works in two ways:

//Expose the ClassLoader used by this ResourceLoader.
ClassLoader getClassLoader(a)
 
//Return a Resource handle for the specified resource location.
Resource getResource(String location)
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The getResource () method determines the Resource implementation to be instantiated based on the Resource path. To get a reference to ResourceLoader, implement the ResourceLoaderAware interface.

Resource banner = resourceLoader.getResource("file:c:/temp/filesystemdata.txt");
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useApplicationContextLoad resources

In Spring, all application contexts implement the ResourceLoader interface. Therefore, all application contexts are available to obtain resource instances.

To get a reference to ApplicationContext, implement the ApplicationContextAware interface.

Resource banner = ctx.getResource("file:c:/temp/filesystemdata.txt");
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useResourceLoaderAwareLoad resources

To illustrate the various examples below, I’ve placed a file with the same name in a different location, and I’ll show you how to load each file.

CustomResourceLoader. Java write as follows, it will print the contents of the loaded resource file to the console.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
 
import org.springframework.context.ResourceLoaderAware;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
 
public class CustomResourceLoader implements ResourceLoaderAware
{
    private ResourceLoader resourceLoader;
 
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }
 
    public void showResourceData(a) throws IOException
    {
        //This line will be changed for all versions of other examples
        Resource banner = resourceLoader.getResource("file:c:/temp/filesystemdata.txt");
 
        InputStream in = banner.getInputStream();
 
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
 
        while (true) {
            String line = reader.readLine();
            if (line == null)
                break; System.out.println(line); } reader.close(); }}Copy the code

The applicationContext.xml file entry for this file is as follows:

<bean id="customResourceLoader" class="cn.howtodoinjava.demo.CustomResourceLoader"></bean>
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To test the CustomResourceLoader bean and call the showResourceData () method, the following code is used:

@SuppressWarnings("resource")
public static void main(String[] args) throws Exception
{
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
 
    CustomResourceLoader customResourceLoader = (CustomResourceLoader) context.getBean("customResourceLoader");
 
    customResourceLoader.showResourceData();
}
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Resource banner = resourceLoader.getResource("file:data.txt");
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Resource banner = resourceLoader.getResource("classpath:classpathdata.txt");
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Resource banner = resourceLoader.getResource("file:c:/temp/filesystemdata.txt");
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Resource banner = resourceLoader.getResource("//howtodoinjava.com/readme.txt");
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<bean id="customResourceLoader" class="com.howtodoinjava.demo.CustomResourceLoader">
 
    <property name="resource">
        <value>classpath:classpathdata.txt</value>
        <! -- or -->
        <value>file:data.txt</value>
    </property>
 
</bean>
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public class CustomResourceLoader {
 
    private Resource resource;
 
    public Resource getResource(a) {
        return resource;
    }
 
    public void setResource(Resource resource) {
        this.resource = resource; }}Copy the code