在MongoDB中，可以使用GridFS保存二进制文件。本文介绍如何使用GridFsTemplate保存和读取图片文件。

1. GridFS – 保存（使用Spring注解方式）

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.config.AbstractMongoConfiguration;
import org.springframework.data.mongodb.gridfs.GridFsTemplate;

import com.mongodb.Mongo;
import com.mongodb.MongoClient;

/**
 * Spring MongoDB configuration file
 *
 */
@Configuration
public class SpringMongoConfig extends AbstractMongoConfiguration{

    @Bean
    public GridFsTemplate gridFsTemplate() throws Exception {
        return new GridFsTemplate(mongoDbFactory(), mappingMongoConverter());
    }

    @Override
    protected String getDatabaseName() {
        return "yourdb";
    }

    @Override
    @Bean
    public Mongo mongo() throws Exception {
        return new MongoClient("127.0.0.1");
    }

}

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.data.mongodb.gridfs.GridFsOperations;

import com.mkyong.config.SpringMongoConfig;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;

/**
 * GridFs example
 *
 * @author zong
 *
 */

public class GridFsAppStore {

    public static void main(String[] args) {

    ApplicationContext ctx =
                     new AnnotationConfigApplicationContext(SpringMongoConfig.class);
    GridFsOperations gridOperations =
                      (GridFsOperations) ctx.getBean("gridFsTemplate");

    DBObject metaData = new BasicDBObject();
    metaData.put("extra1", "anything 1");
    metaData.put("extra2", "anything 2");

    InputStream inputStream = null;
    try {
        inputStream = new FileInputStream("/Users/mkyong/Downloads/testing.png");
        gridOperations.store(inputStream, "testing.png", "image/png", metaData);

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

        System.out.println("Done");
    }

}

使用MongoDB控制台查看保存的文件：

> show dbs
yourdb  0.203125GB

> use yourdb
switched to db yourdb

> show collections
fs.chunks
fs.files
system.indexes

> db.fs.files.find()
{ "_id" : ObjectId("51641c5630045c9b3db35afc"), "chunkSize" : NumberLong(262144),
"length" : NumberLong(4238), "md5" : "9969527cd95a5a573f15e953f0036800", "filename" : "testing.png",
"contentType" : "image/png", "uploadDate" : ISODate("2013-04-09T13:49:10.104Z"),
"aliases" : null, "metadata" : { "extra1" : "anything 1", "extra2" : "anything 2" } }
>

> db.fs.chunks.find()
{ "_id" : ObjectId("51641c5630045c9b3db35afd"),
"files_id" : ObjectId("51641c5630045c9b3db35afc"), "n" : 0,
"data" : BinData(0,"/9j/4AAQSkZJRgABAgAAZ......EQH/9k=") }

图片信息保存在fs.files，图片的二进制流保存在fs.chunks，通过_id和files_id关联。

2. GridFS – 读取（使用xml方式）

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:mongo="http://www.springframework.org/schema/data/mongo"
    xsi:schemaLocation="http://www.springframework.org/schema/data/mongo
       http://www.springframework.org/schema/data/mongo/spring-mongo.xsd
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <mongo:db-factory id="mongoDbFactory" dbname="yourdb" />
    <mongo:mapping-converter id="converter" />

    <bean name="gridFsTemplate"
        class="org.springframework.data.mongodb.gridfs.GridFsTemplate">
        <constructor-arg ref="mongoDbFactory" />
        <constructor-arg ref="converter" />
    </bean>

</beans>

import java.io.IOException;
import java.util.List;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.GenericXmlApplicationContext;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.gridfs.GridFsOperations;

import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
import com.mongodb.gridfs.GridFSDBFile;

/**
 * GridFs example
 *
 * @author zong
 *
 */

public class GridFsAppRead {

    public static void main(String[] args) {

    ApplicationContext ctx =
              new GenericXmlApplicationContext("SpringConfig.xml");
    GridFsOperations gridOperations =
              (GridFsOperations) ctx.getBean("gridFsTemplate");

    List<GridFSDBFile> result = gridOperations.find(
               new Query().addCriteria(Criteria.where("filename").is("testing.png")));

    for (GridFSDBFile file : result) {
        try {
            System.out.println(file.getFilename());
            System.out.println(file.getContentType());

            //save as another image
            file.writeTo("/Users/mkyong/Downloads/new-testing.png");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    System.out.println("Done");

    }
}