Java对MongoDB中的数据查询处理

Java语言标准的数据库时MySQL，但是有些时候也会用到MongoDB，这次Boss交代处理MongoDB，所以讲代码以及思路记录下了

摸索的过程，才发现软件的适用还是很重要的啊！！！

我连接的MongoDB的数据是远程数据库，连接本地数据库的方法网上有很多：

//连接到MongoDB服务 如果是远程连接可以替换“localhost”为服务器所在IP地址
        //ServerAddress()两个参数分别为 服务器地址 和 端口
        ServerAddress serverAddress = new ServerAddress("106.12.34.175",27017);
        List<ServerAddress> addrs = new ArrayList<ServerAddress>();
        addrs.add(serverAddress);

        //MongoCredential.createScramSha1Credential()三个参数分别为 用户名 数据库名称 密码
        MongoCredential credential = MongoCredential.createScramSha1Credential("***", "***", "***".toCharArray());
        List<MongoCredential> credentials = new ArrayList<MongoCredential>();
        credentials.add(credential);

        //通过连接认证获取MongoDB连接
        MongoClient mongoClient = new MongoClient(addrs,credentials);

        //连接到数据库
        MongoDatabase mongoDatabase = mongoClient.getDatabase("***");
        MongoCollection<Document> collection  = mongoDatabase.getCollection("dianping_city");

        //查询过程
        BasicDBObject query = new BasicDBObject();
        query.put("city_num","xxx");

        //查询结果
        //MongoCursor<Document> cursor = collection.find(query).skip(0).limit(10).iterator();
        MongoCursor<Document> cursor = collection.find(query).skip(0).iterator();

这样查询结果就有了，下面要将查询结果存储为CSV文件，我这里实现的是对查询的结果进行存储（对于多条的查询数据，也一并放入CSV文件中）；存储的过程需要注意：从MongoDB返回的数据类型，多条数据类型在CSV文件中的对齐。

List<String> resultList = new LinkedList<>();
        List<String> tableList = new ArrayList<>();
        while (cursor.hasNext()) {
            String  jsonString = new String();
            jsonString = cursor.next().toJson();
            int length = jsonString.length();
            jsonString = "[{" + jsonString.substring(jsonString.indexOf(",") + 1, length) + "]";
            System.out.println(jsonString);

            JSONArray jsonArray = new JSONArray(jsonString);
            JSONObject jsonObject = jsonArray.getJSONObject(0);
            try {
                if(tableList.size() == 0) {
                    StringBuilder stringKey = new StringBuilder();
                    Iterator iterator = jsonObject.keys();
                    while (iterator.hasNext()) {
                        String key = (String) iterator.next();
                        if(key.compareTo("shophours") == 0){continue;}
                        tableList.add(key);
                    stringKey.append(key).append(',');
                    }
                    resultList.add(stringKey.deleteCharAt(stringKey.length()-1).toString());
                }
                StringBuilder stringValue = new StringBuilder();
                for(String entry: tableList){
                    String value = new String();
                    if(!jsonObject.has(entry)){
                        value = "null";
                    }
                    else {
                        value = jsonObject.get(entry).toString();
                    }
                    stringValue.append(value).append(',');
                }
                resultList.add(stringValue.deleteCharAt(stringValue.length()-1).toString());
            }
            catch (JSONException e){
                e.printStackTrace();
            }
        }

总结一下：之前没有处理过MongoDB，所以在这个small task上花了点时间，不过最后也有收获，至少MongoDB与Java相关的坑踩了一部分，为以后积累经验嘛。

整体代码：

 package MongoDB;

 import com.mongodb.*;
 import com.mongodb.client.MongoCollection;
 import com.mongodb.client.MongoCursor;
 import com.mongodb.client.MongoDatabase;
 import org.bson.Document;
 import org.json.*;
 import java.io.*;
 import java.util.*;

 public class outputData {
     public static void main(String[] args){
         //连接到MongoDB服务 如果是远程连接可以替换“localhost”为服务器所在IP地址
         //ServerAddress()两个参数分别为 服务器地址 和 端口
         ServerAddress serverAddress = new ServerAddress("IP",port);
         List<ServerAddress> addrs = new ArrayList<ServerAddress>();
         addrs.add(serverAddress);

         //MongoCredential.createScramSha1Credential()三个参数分别为 用户名 数据库名称 密码
         MongoCredential credential = MongoCredential.createScramSha1Credential("***", "***", "***".toCharArray());
         List<MongoCredential> credentials = new ArrayList<MongoCredential>();
         credentials.add(credential);

         //通过连接认证获取MongoDB连接
         MongoClient mongoClient = new MongoClient(addrs,credentials);

         //连接到数据库
         MongoDatabase mongoDatabase = mongoClient.getDatabase("****");
         MongoCollection<Document> collection  = mongoDatabase.getCollection("dianping_city");

         //查询过程
         BasicDBObject query = new BasicDBObject();
         query.put("city_num","xxx");

         //查询结果
         //MongoCursor<Document> cursor = collection.find(query).skip(0).limit(10).iterator();
         MongoCursor<Document> cursor = collection.find(query).skip(0).iterator();

         List<String> resultList = new LinkedList<>();
         List<String> tableList = new ArrayList<>();
         while (cursor.hasNext()) {
             String  jsonString = new String();
             jsonString = cursor.next().toJson();
             int length = jsonString.length();
             jsonString = "[{" + jsonString.substring(jsonString.indexOf(",") + 1, length) + "]";
             System.out.println(jsonString);

             JSONArray jsonArray = new JSONArray(jsonString);
             JSONObject jsonObject = jsonArray.getJSONObject(0);
             try {
                 if(tableList.size() == 0) {
                     StringBuilder stringKey = new StringBuilder();
                     Iterator iterator = jsonObject.keys();
                     while (iterator.hasNext()) {
                         String key = (String) iterator.next();
                         if(key.compareTo("shophours") == 0){continue;}
                         tableList.add(key);
                     stringKey.append(key).append(',');
                     }
                     resultList.add(stringKey.deleteCharAt(stringKey.length()-1).toString());
                 }
                 StringBuilder stringValue = new StringBuilder();
                 for(String entry: tableList){
                     String value = new String();
                     if(!jsonObject.has(entry)){
                         value = "null";
                     }
                     else {
                         value = jsonObject.get(entry).toString();
                     }
                     stringValue.append(value).append(',');
                 }
                 resultList.add(stringValue.deleteCharAt(stringValue.length()-1).toString());
             }
             catch (JSONException e){
                 e.printStackTrace();
             }
         }
         cursor.close();

         try {
             File csv = new File("C:\\Users\\Administrator\\Desktop\\tmp2.csv");
             OutputStreamWriter outStream = null;
             outStream = new OutputStreamWriter(new FileOutputStream(csv), "GBK");
             BufferedWriter bw = new BufferedWriter(outStream);
            for(String entry : resultList){
             // 添加新的数据行
                 bw.write(entry.toCharArray());
                 bw.newLine();
            }
             bw.close();
         }
         catch (FileNotFoundException e) {
             // File对象的创建过程中的异常捕获
             e.printStackTrace();
         } catch (IOException e) {
             // BufferedWriter在关闭对象捕捉异常
             e.printStackTrace();
         }
         System.out.println("MongoDB connect successfully: "+"mongoDatabase = " + mongoDatabase.getName());
     }
 }

最后贴上几个为以后做准备的链接：

MongoDB安装：http://www.cnblogs.com/lzrabbit/p/3682510.html

Java下MongoDB查询：https://www.cnblogs.com/luoaz/p/4691639.html