GridFS文件操作

1. GridFS介绍

GridFS是MongoDB提供的用于持久化存储文件的模块，CMS使用MongoDB存储数据，使用GridFS可以快速集成
开发。
它的工作原理是：
在GridFS存储文件是将文件分块存储，文件会按照256KB的大小分割成多个块进行存储，GridFS使用两个集合
（collection）存储文件，一个集合是chunks, 用于存储文件的二进制数据；一个集合是files，用于存储文件的元数据信息（文件名称、块大小、上传时间等信息）。
从GridFS中读取文件要对文件的各各块进行组装、合并。
详细参考：https://docs.mongodb.com/manual/core/gridfs/

2. GridFS 存取文件测试

2.1 新建项目配置pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo-monogo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo-monogo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-mongodb</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2.2 在application.yml配置MongoDB

spring:
  data:
    mongodb:
      uri: mongodb://root::27017
      database: xc_cms

2.3 GridFS存取文件测试

1、存文件
使用GridFsTemplate存储文件测试代码：
向测试程序注入GridFsTemplate。

package com.example.demomonogo;

import org.bson.types.ObjectId;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.mongodb.gridfs.GridFsTemplate;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;

@SpringBootTest
class DemoMonogoApplicationTests {
    @Autowired
    GridFsTemplate gridFsTemplate;

    @Test
    public void testGridFs() throws FileNotFoundException {
        //要存储的文件
        File file = new File("D:\\test\\user_selected.png");
        //定义输入流
        FileInputStream inputStram = new FileInputStream(file);
        //向GridFS存储文件
        ObjectId objectId = gridFsTemplate.store(inputStram, "user_selected.png", "image/png");
        //得到文件ID
        String fileId = objectId.toString();
        System.out.println(fileId);
    }

}

文件以及成功被存入到GridFS

2.4 读取文件

1）在config包中定义MongoDB的配置类，如下：
GridFSBucket用于打开下载流对象

package com.example.demomonogo.config;

/**
 * @author john
 * @date 2019/12/21 - 10:39
 */


import com.mongodb.MongoClient;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.GridFSBuckets;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MongoConfig {
    @Value("${spring.data.mongodb.database}")
    String db;

    @Bean
    public GridFSBucket getGridFSBucket(MongoClient mongoClient) {
        MongoDatabase database = mongoClient.getDatabase(db);
        GridFSBucket bucket = GridFSBuckets.create(database);
        return bucket;
    }
}

2）测试代码如下

package com.example.demomonogo;

import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.GridFSDownloadStream;
import com.mongodb.client.gridfs.model.GridFSFile;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.gridfs.GridFsResource;
import org.springframework.data.mongodb.gridfs.GridFsTemplate;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

@SpringBootTest
class DemoMonogoApplicationTests {
    @Autowired
    GridFsTemplate gridFsTemplate;

    @Autowired
    GridFSBucket gridFSBucket;

    @Test
    public void queryFile() throws IOException {
        String fileId = "5dfd851306322e6b12057a40";
        //根据id查询文件
        GridFSFile gridFSFile =
                gridFsTemplate.findOne(Query.query(Criteria.where("_id").is(fileId)));
        //打开下载流对象
        GridFSDownloadStream gridFSDownloadStream =
                gridFSBucket.openDownloadStream(gridFSFile.getObjectId());
        //创建gridFsResource，用于获取流对象
        GridFsResource gridFsResource = new GridFsResource(gridFSFile, gridFSDownloadStream);
        //获取流中的数据
        InputStream inputStream = gridFsResource.getInputStream();
        File f1 = new File("D:\\test\\get.png");
        if (!f1.exists()) {
            f1.getParentFile().mkdirs();
        }
        byte[] bytes = new byte[1024];
        // 创建基于文件的输出流
        FileOutputStream fos = new FileOutputStream(f1);
        int len = 0;
        while ((len = inputStream.read(bytes)) != -1) {
            fos.write(bytes, 0, len);
        }
        inputStream.close();
        fos.close();

    }

}

2.5 删除文件

package com.example.demomonogo;


import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.gridfs.GridFsTemplate;

import java.io.IOException;

@SpringBootTest
class DemoMonogoApplicationTests {
    @Autowired
    GridFsTemplate gridFsTemplate;

    //删除文件
    @Test
    public void testDelFile() throws IOException {
        //根据文件id删除fs.files和fs.chunks中的记录
        gridFsTemplate.delete(Query.query(Criteria.where("_id").is("5dfd851306322e6b12057a40")));
    }

}