首先列出所需部分数据

集合user：

/* 1 */{    "_id" : 1.0,    "hire" : ISODate("2016-12-15T02:52:04.630Z")}/* 2 */{    "_id" : 2.0,    "chinese" : 80.0,    "math" : 90.0,    "name" : "lisi"}/* 3 */{    "_id" : 3.0,    "chinese" : 70.0,    "math" : 90.0,    "name" : "wangwu"}/* 4 */{    "_id" : 4.0,    "name" : "zs",    "chinese" : 50,    "math" : 60}

集合date：

/* 1 */{    "_id" : 1,    "hire" : ISODate("2016-12-20T08:37:15.705Z")}

集合mycol：

/* 1 */{    "_id" : ObjectId("57ec6d0d7fbbc90bccc18e13"),    "title" : "MongoDB1",    "description" : "nosql",    "likes" : 0,    "by_user" : "lzq"}/* 2 */{    "_id" : ObjectId("57ec6d0d7fbbc90bccc18e14"),    "title" : "MongoDB2",    "description" : "nosql",    "likes" : 2,    "by_user" : "lzq"}/* 3 */{    "_id" : ObjectId("57ec6d0d7fbbc90bccc18e15"),    "title" : "MongoDB3",    "description" : "nosql",    "likes" : 3,    "by_user" : "lzq"}

集合tree：

/* 1 */{    "_id" : ObjectId("584e47110dc763ff7e50347b"),    "management" : {        "organization" : [             {                "name" : "Organizational institution",                "index" : 1.0            },             {                "name" : "Company files",                "index" : 2.0            },             {                "name" : "department files",                "index" : 3.0            }        ],        "authority" : [             {                "name" : "user",                "sequence" : 100.0            },             {                "name" : "role",                "sequence" : 102.0            },             {                "name" : {                    "source_register" : [                         {                            "name" : "button"                        },                         {                            "name" : "field"                        }                    ]                },                "sequence" : 103.0            }        ]    },    "num" : 1.0}

Code：

聚合操作所有JSON定义类

package db.mongo.feature.util;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.JSONArray;import com.alibaba.fastjson.JSONObject;import java.util.Arrays;import java.util.List;public class AggregateJson{    //$project操作    public static final String USERPROJECT = "{$project:{\"userid\":\"$_id\",\"_id\":0}}";    //$project操作与$add操作(示例：perStuTotalScore)    public static final String PROJECT_ADD = "{\n" +            "    $project:{\n" +            "        chinese:1,\n" +            "        math:1,\n" +            "        totalgrade:{$add:[\"$chinese\",\"$math\"]}\n" +            "        }\n" +            "   }";    //日期操作(示例date集合)    public static final String DATE_EXPRESSION = "{\n" +            "       $project:\n" +            "         {\n" +            "         year: { $year: \"$hire\" },\n" +            "           month: { $month: \"$hire\" },\n" +            "           day: { $dayOfMonth: \"$hire\" },\n" +            "           hour: { $hour: \"$hire\" },\n" +            "           minutes: { $minute: \"$hire\" },\n" +            "           seconds: { $second: \"$hire\" },\n" +            "           milliseconds: { $millisecond: \"$hire\" },\n" +            "           dayOfYear: { $dayOfYear: \"$hire\" },\n" +            "           dayOfWeek: { $dayOfWeek: \"$hire\" },\n" +            "           week: { $week: \"$hire\" }\n" +            "         }\n" +            "     }";    //截取name的第一个字节，与.和$sex值拼接(示例mycol集合)    public static final String[] PROJECT_CONCAT_SUBSTR = {"{$project:{\"title\":{\n" +            "  $concat:[\"$by_user\",\".\",{$substr:[\"$title\",5,8]}]\n" +            "  }}}","{$limit:2}"};    //比较两个数值大小(示例user集合)    public static final String PROJECT_CMP = "{\n" +            "    $project:{\n" +            "        chinese:1,\n" +            "        math:1,\n" +            "        compareTo:{$cmp:[\"$chinese\",\"$math\"]}\n" +            "        }\n" +            "   }";    public static final String[] PRJECT_GROUP_SORT_LIMIT = {"{   \n" +            "        $project: {\n" +            "        \"name\": 1,\n" +            "        \"chinese\":1,\n" +            "        \"math\":1\n" +            "        }\n" +            "    }", "{ $group: { _id: \"$name\" ,totalScore:{$sum:{$add:[\"$chinese\",\"$math\"]}}} }",  "{\n" +            "        $sort: {\n" +            "            \"totalScore\": -1\n" +            "        }\n" +            "    }", "{\n" +            "        $limit: 3\n" +            "    }"};    public static final String PROJECT_COND = "{\n" +            "         $project:\n" +            "           {\n" +            "             \n" +            "             discount:\n" +            "               {\n" +            "               $cond: { if: { $gte: [ \"$chinese\", 60 ] }, then: \"$chinese\", else: \"不合格\" }\n" +            "               }\n" +            "           }\n" +            "      }";    public static final String UNWIND = "{$unwind:\"$management.organization\"}";    public static final String DISTINCT = "{\"distinct\":\"user\",\"key\":\"chinese\"}";}

聚合操作类：

package db.mongo.feature;import com.mongodb.AggregationOptions;import com.mongodb.GroupCommand;import com.mongodb.MongoClient;import com.mongodb.client.*;import com.mongodb.client.model.Filters;import com.mongodb.client.model.FindOptions;import com.mongodb.client.model.Projections;import com.mongodb.client.model.Sorts;import com.mongodb.operation.GroupOperation;import db.mongo.feature.util.AggregateJson;import db.mongo.util.Constants;import org.apache.log4j.Logger;import org.bson.BsonDocument;import org.bson.Document;import org.bson.conversions.Bson;import org.junit.Before;import org.junit.Test;import java.util.ArrayList;import java.util.Arrays;import java.util.List;public class MongoAggregate {    /*    聚合：对集合中的文档进行变换和组合,可对文档进行一连串的处理.    $match $project $group $unwind $limit $skip $sort...    需要将聚合操作传给aggregate，db.articles.aggregate如果不是从数据库返回的集合，那么Mongo Shell会自动迭代20次    MongoDB不允许管道占用很多内存，如20%,会直接报错*//*$project代表将articles集合投射出author字段，结果集中只包含_id和author字段;    $match匹配以x开头的author;    然后"_id":"$author"指定了分组字段author;    $group会在结果集中创建count字段,执行结果类似这样的结构:{ "_id" : "xiaobao", "count" : 10 };    $sort按照count字段将以上结果排序;    $limit将限制返回结果集的前三个文档    "$filename"是为了引用字段的值*/    private static Logger logger = Logger.getLogger(MongoAggregate.class);    MongoDatabase database = null;    public  MongoCollection
    
      getCollection(String collectionName) {        return this.database.getCollection(collectionName);    }    @Before    public void connect(){        MongoClient client = new MongoClient(Constants.MONGO_HOST,Constants.MONGO_PORT);        //当前获取这个数据库时并没有这个名称的数据库，不会报错，当有数据添加的时候才会创建        database = client.getDatabase("test");    }    /**     * @param collection 接收一个指定的mongo集合     * @param jsons      接收json数组，用来聚合查询时解析多个json过滤条件     *     *  接收多个json字符串     */    public void aggregate(MongoCollection
     
       collection,String... jsons){        List
      
        pileline = new ArrayList
       
        ();        for (String json : jsons){            pileline.add(Document.parse(json));        }        List
        
          results = collection.aggregate(pileline).into(new ArrayList
         
          ()); for (Document cur : results) { System.out.println(cur.toJson()); } } /** * 测试所有聚合操作 */ @Test public void testAggregate() { /*$project操作 MongoCollection
          
            collection = getCollection("user"); aggregate(collection, AggregateJson.USERPROJECT); */ /*查询日期 MongoCollection
           
             collection = getCollection("date"); aggregate(collection, AggregateJson.DATE_EXPRESSION);*/ //$project操作与$add操作(示例：perStuTotalScore) /*MongoCollection
            
              collection = getCollection("user"); aggregate(collection, AggregateJson.PROJECT_ADD);*/ //截取name的第一个字节，与.和$sex值拼接(示例mycol集合) /*MongoCollection
             
               collection = getCollection("mycol"); aggregate(collection, AggregateJson.PROJECT_CONCAT_SUBSTR);*/ //学生总成绩排名前三甲 /*MongoCollection
              
                collection = getCollection("user"); aggregate(collection, AggregateJson.PRJECT_GROUP_SORT_LIMIT);*/ /*比较成绩高低，返回比较记录，类似java的Comparable比较器的compareTo方法，返回1,0,-1*/ /*MongoCollection
               
                 collection = getCollection("user"); aggregate(collection, AggregateJson.PROJECT_CMP);*/ //判断语文成绩大小，如果大于60分显示其分数，如果小于60分则显示不合格,如果没有这个字段也会显示不合格 /*MongoCollection
                
                  collection = getCollection("user"); aggregate(collection, AggregateJson.PROJECT_COND);*/ //将数组的每个值拆分为单独的文档 /*MongoCollection
                 
                   collection = getCollection("tree"); aggregate(collection, AggregateJson.UNWIND);*/ //distinct找出给定键不同的值,找出不同的语文成绩/* Document document = database.runCommand(Document.parse(AggregateJson.DISTINCT)); System.out.println(document.toJson());*/ }}