概述

Spring對各種底層資源,比如檔案系統中的一個檔案，classpath上的一個檔案，或者一個網路URL，統一抽象為介面Resource來表示 。

org.springframework.core.io // 介面Resource所在包

因為每個底層檔案都可以以一個只讀InputStream的方式開啟，所以Resource介面繼承自介面InputStreamSource。InputStreamSource介面中定義了方法getInputStream()用於返回開啟該資源所對應的輸入流。

實現類

Spring針對不同的底層資源型別提供了相應的實現。如下表所示 :

使用例項

package test.resources;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import org.springframework.core.io.*;

import java.io.FileInputStream;
import java.io.InputStream;

@Slf4j
public class SpringResourceDemo {
    /**
     * 描述一個Resource例項
     *
     * @param resource
     * @throws Exception
     */
    void describe(Resource resource) throws Exception {
        log.info("====================================");
        log.info("toString : {}", resource.toString());
        log.info("contentLength : {}", resource.contentLength());
        log.info("exists : {}", resource.exists());
        log.info("getDescription : {}", resource.getDescription());
        log.info("isReadable : {}", resource.isReadable());
        log.info("isOpen : {}", resource.isOpen());
        log.info("getFilename : {}", resource.getFilename());
        log.info("isFile : {}", resource.isFile());
        if (resource.isFile()) {
            // getFile()僅針對檔案型別Resource有效,可以是檔案系統檔案或者classpath上的檔案
            log.info("getFile : {}", resource.getFile());
        }

        if (!((resource instanceof ByteArrayResource) || (resource instanceof InputStreamResource))) {
            // 以下三個屬性針對 ByteArrayResource/InputStreamResource 型別資源無效，呼叫的話會丟擲異常
            log.info("lastModified : {}", resource.lastModified());
            log.info("getURI : {}", resource.getURI());
            log.info("getURL : {}", resource.getURL());
        }
    }

    @Test
    public void test() throws Exception {
        {
            Resource resource = new ClassPathResource("test/resources/SpringResourceDemo.class");
            describe(resource);
        }

        {// test.txt 是當前磁碟卷根目錄下一個存在的檔案，內容是:Test Spring Resource
            Resource resource = new FileSystemResource("/test.txt");
            describe(resource);
        }

        {//
            Resource resource = new UrlResource("https://docs.spring.io");
            describe(resource);
        }

        {//
            Resource resource = new ByteArrayResource("Hello".getBytes());
            describe(resource);
        }


        {// test.txt 是當前磁碟卷根目錄下一個存在的檔案，內容是:Test Spring Resource
            InputStream is = new FileInputStream("/test.txt");
            Resource resource = new InputStreamResource(is);
            describe(resource);
        }
    }
}

上面的測試程式碼執行輸出如下:

====================================
toString : class path resource [test/resources/SpringResourceDemo.class]
contentLength : 2838
exists : true
getDescription : class path resource [test/resources/SpringResourceDemo.class]
isReadable : true
isOpen : false
getFilename : SpringResourceDemo.class
isFile : true
getFile : D:\springboot-tut-zero\target\test-classes\test\resources\SpringResourceDemo.class
lastModified : 1542634668385
getURI : file:/D:/springboot-tut-zero/target/test-classes/test/resources/SpringResourceDemo.class
getURL : file:/D:/springboot-tut-zero/target/test-classes/test/resources/SpringResourceDemo.class
====================================
toString : file [D:\test.txt]
contentLength : 20
exists : true
getDescription : file [D:\test.txt]
isReadable : true
isOpen : false
getFilename : test.txt
isFile : true
getFile : \test.txt
lastModified : 1542633020067
getURI : file:/D:/test.txt
getURL : file:/D:/test.txt
====================================
toString : URL [https://docs.spring.io]
contentLength : -1
exists : true
getDescription : URL [https://docs.spring.io]
isReadable : true
isOpen : false
getFilename :
isFile : false
lastModified : 0
getURI : https://docs.spring.io
getURL : https://docs.spring.io
====================================
toString : Byte array resource [resource loaded from byte array]
contentLength : 5
exists : true
getDescription : Byte array resource [resource loaded from byte array]
isReadable : true
isOpen : false
getFilename : null
isFile : false
====================================
toString : InputStream resource [resource loaded through InputStream]
contentLength : 20
exists : true
getDescription : InputStream resource [resource loaded through InputStream]
isReadable : true
isOpen : true
getFilename : null
isFile : false