如何在java中从Mongo子文档中获取特定数据？

我试图获取mongo文档中特定列值的数据，但它显示了整个数据

以下是mongo文件：

{
    "_id" : ObjectId("59db2321811a592384865711"),
    "User_ID" : "demo",
    "Project_ID" : "demo-1",
    "Project_Information" : {
        "Project_Description" : "Sample",
        "Primary_Building_Type" : "Office",
        "State" : "AR",
        "Analysis_Type" : "1",
        "Project_Billing_Number" : "WY",
        "Country" : "USA",
        "Climate_Zone" : "3A",
        "Zip_Code" : "71611"
        "City" : "WA",
        "Units" : "IP"
    }
}

我要获取以下输出：

[
    {
        "User_ID": "demo",
        "Project_Description": "Sample"
}]

我尝试使用dot:

项目信息。项目描述

。代码如下：

public Object[] addDemo1(String User_ID) throws Exception {
    DB db = ConnectToDB.getConnection();
    Properties prop = new Properties();
    InputStream input = null;
    input = GetProjectStatus.class.getClassLoader().getResourceAsStream("config.properties");
    prop.load(input);
    String col = prop.getProperty("COLLECTION_PI");
    System.out.println("data is.." + col);
    DBCollection collection = db.getCollection(col);
    BasicDBObject obj = new BasicDBObject();
    BasicDBObject fields = new BasicDBObject();
    BasicDBObject fields2 = new BasicDBObject();
    List<DBObject> obj1 = null;
    if (User_ID != null && !User_ID.equals("") && User_ID.length() > 0) {
        obj.put("User_ID", User_ID);
        fields.put("_id", 0);
        fields.put("User_ID", 1);
        fields.put("Project_ID", 1);
        fields.append("Project_Information.Project_Description", "Project_Description");
        BasicDBObject fields1 = new BasicDBObject();
        fields1.put("User_ID", User_ID);
    }
    DBCursor cursor = collection.find(obj, fields);
    System.out.println("count  is:" + cursor.count());
    obj1 = cursor.toArray();
    System.out.println("" + obj1);
    cursor.close();
    db.getMongo().close();
    return obj1.toArray();

}

public对象[]addDemo1（字符串用户ID）引发异常{
DB DB=ConnectToDB.getConnection（）；
Properties prop=新属性（）；
InputStream输入=null；
input=GetProjectStatus.class.getClassLoader（）.getResourceAsStream（“config.properties”）；
道具载荷（输入）；
String col=prop.getProperty（“COLLECTION_PI”）；
System.out.println（“数据为..”+col）；
DBCollection=db.getCollection（col）；
BasicDBObject对象=新的BasicDBObject（）；
BasicDBObject字段=新建BasicDBObject（）；
BasicDBObject字段S2=新的BasicDBObject（）；
列表obj1=null；
如果（User_ID！=null&&！User_ID.equals（“”&&User_ID.length（）>0）{
obj.put（“用户ID”，用户ID）；
字段。放置（“\u id”，0）；
字段。put（“用户ID”，1）；
字段。put（“项目ID”，1）；
字段。追加（“项目信息。项目描述”，“项目描述”）；
BasicDBObject字段1=新的BasicDBObject（）；
字段1.put（“用户ID”，用户ID）；
}
DBCursor=collection.find（对象，字段）；
System.out.println（“计数为：+cursor.count（））；
obj1=游标。toArray（）；
系统输出打印项次（“+obj1”）；
cursor.close（）；
db.getMongo（）.close（）；
返回obj1.toArray（）；
}

但是它显示了

项目信息的整个结构

请具体说明如何实现这一点。谢谢您的帮助。
Java库不允许您使用dot直接访问

他们有内置的getter和setter方法

您没有提到您正在使用的软件包

以下是您需要的查询：

db.mycol.find({},{User_ID:1,"Project_Information.Project_Description":1})

它将提供：

{ "_id" : ObjectId("59db2321811a592384865711"),
    "User_ID" : "demo",
    "Project_Information" : { "Project_Description" : "Sample" }
}

您必须以包接受的任何格式转换查询

以下是一个教程：
Java库不允许您使用dot直接访问

他们有内置的getter和setter方法

您没有提到您正在使用的软件包

以下是您需要的查询：

db.mycol.find({},{User_ID:1,"Project_Information.Project_Description":1})

它将提供：

{ "_id" : ObjectId("59db2321811a592384865711"),
    "User_ID" : "demo",
    "Project_Information" : { "Project_Description" : "Sample" }
}

您必须以包接受的任何格式转换查询

以下是一个教程：
使用2.x MongoDB Java驱动程序

下面是一个使用MongoDB 2.x Java驱动程序的示例：

DBCollection collection = mongoClient.getDB("stackoverflow").getCollection("demo");

BasicDBObject filter = new BasicDBObject();
BasicDBObject projection = new BasicDBObject();

// project on "Project_Information.Project_Description"
projection.put("Project_Information.Project_Description", 1);

DBCursor documents = collection.find(filter, projection);

for (DBObject document : documents) {
    // the response contains a sub document under the key: "Project_Information"
    DBObject projectInformation = (DBObject) document.get("Project_Information");
    // the "Project_Description" is in this sub document
    String projectDescription = (String) projectInformation.get("Project_Description");

    // prints "Sample"
    System.out.println(projectDescription);

    // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
    Object[] r = new Object[] {projectDescription};

    // prints the entire projected document e.g. 
    // { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
    System.out.println(document.toString());
}

    // this finds all documents in a given collection (note: no parameter supplied to the find() call) 
    // and for each document it projects on Project_Information.Project_Description
    FindIterable<Document> documents =
            mongoClient.getDatabase("...").getCollection("...")
               .find()
               // for each attrbute you want to project you must include its dot notation path and the value 1 ... 
               // this is the equivalent of specifying {'Project_Information.Project_Description': 1} in the MongoDB shell
               .projection(new Document("Project_Information.Project_Description", 1));

    for (Document document : documents) {
        // the response contains a sub document under the key: "Project_Information"
        Document projectInformation = (Document) document.get("Project_Information");
        // the "Project_Description" is in this sub document
        String projectDescription = projectInformation.getString("Project_Description");

        // prints "Sample"
        System.out.println(projectDescription);

        // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
        Object[] r = new Object[] {projectDescription};

        // prints the entire projected document e.g. { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
        System.out.println(document.toJson());
    }

使用3.x MongoDB Java驱动程序

下面是一个使用MongoDB 3.x Java驱动程序的示例：

DBCollection collection = mongoClient.getDB("stackoverflow").getCollection("demo");

BasicDBObject filter = new BasicDBObject();
BasicDBObject projection = new BasicDBObject();

// project on "Project_Information.Project_Description"
projection.put("Project_Information.Project_Description", 1);

DBCursor documents = collection.find(filter, projection);

for (DBObject document : documents) {
    // the response contains a sub document under the key: "Project_Information"
    DBObject projectInformation = (DBObject) document.get("Project_Information");
    // the "Project_Description" is in this sub document
    String projectDescription = (String) projectInformation.get("Project_Description");

    // prints "Sample"
    System.out.println(projectDescription);

    // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
    Object[] r = new Object[] {projectDescription};

    // prints the entire projected document e.g. 
    // { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
    System.out.println(document.toString());
}

    // this finds all documents in a given collection (note: no parameter supplied to the find() call) 
    // and for each document it projects on Project_Information.Project_Description
    FindIterable<Document> documents =
            mongoClient.getDatabase("...").getCollection("...")
               .find()
               // for each attrbute you want to project you must include its dot notation path and the value 1 ... 
               // this is the equivalent of specifying {'Project_Information.Project_Description': 1} in the MongoDB shell
               .projection(new Document("Project_Information.Project_Description", 1));

    for (Document document : documents) {
        // the response contains a sub document under the key: "Project_Information"
        Document projectInformation = (Document) document.get("Project_Information");
        // the "Project_Description" is in this sub document
        String projectDescription = projectInformation.getString("Project_Description");

        // prints "Sample"
        System.out.println(projectDescription);

        // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
        Object[] r = new Object[] {projectDescription};

        // prints the entire projected document e.g. { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
        System.out.println(document.toJson());
    }

//这将查找给定集合中的所有文档（注意：没有为find（）调用提供参数）
//对于每个it项目的文档，请参见项目信息。项目描述
可查找文件=
mongoClient.getDatabase（“…”）.getCollection（“…”）
.find（）
//对于要投影的每个属性，必须包含其点表示法路径和值1。。。
//这相当于在MongoDB shell中指定{'Project_Information.Project_Description'：1}
.项目（新文件（“项目信息.项目说明”，1））；
用于（文档：文档）{
//响应包含一个子文档，位于“项目信息”项下
文档项目信息=（文档）Document.get（“项目信息”）；
//“项目描述”在本子文件中
String projectDescription=projectInformation.getString（“项目描述”）；
//打印“样本”
System.out.println（项目描述）；
//要在对象[]中返回此单个字符串值（如OP所示），只需像这样创建对象[]，然后返回它。。。
对象[]r=新对象[]{projectDescription}；
//打印整个投影文档，例如{“\u id”：{“$oid”：“59db221811a592384865711”}，“项目信息”：{“项目描述”：“示例”}
System.out.println（document.toJson（））；
}
使用2.x MongoDB Java驱动程序

下面是一个使用MongoDB 2.x Java驱动程序的示例：

DBCollection collection = mongoClient.getDB("stackoverflow").getCollection("demo");

BasicDBObject filter = new BasicDBObject();
BasicDBObject projection = new BasicDBObject();

// project on "Project_Information.Project_Description"
projection.put("Project_Information.Project_Description", 1);

DBCursor documents = collection.find(filter, projection);

for (DBObject document : documents) {
    // the response contains a sub document under the key: "Project_Information"
    DBObject projectInformation = (DBObject) document.get("Project_Information");
    // the "Project_Description" is in this sub document
    String projectDescription = (String) projectInformation.get("Project_Description");

    // prints "Sample"
    System.out.println(projectDescription);

    // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
    Object[] r = new Object[] {projectDescription};

    // prints the entire projected document e.g. 
    // { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
    System.out.println(document.toString());
}

    // this finds all documents in a given collection (note: no parameter supplied to the find() call) 
    // and for each document it projects on Project_Information.Project_Description
    FindIterable<Document> documents =
            mongoClient.getDatabase("...").getCollection("...")
               .find()
               // for each attrbute you want to project you must include its dot notation path and the value 1 ... 
               // this is the equivalent of specifying {'Project_Information.Project_Description': 1} in the MongoDB shell
               .projection(new Document("Project_Information.Project_Description", 1));

    for (Document document : documents) {
        // the response contains a sub document under the key: "Project_Information"
        Document projectInformation = (Document) document.get("Project_Information");
        // the "Project_Description" is in this sub document
        String projectDescription = projectInformation.getString("Project_Description");

        // prints "Sample"
        System.out.println(projectDescription);

        // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
        Object[] r = new Object[] {projectDescription};

        // prints the entire projected document e.g. { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
        System.out.println(document.toJson());
    }

使用3.x MongoDB Java驱动程序

下面是一个使用MongoDB 3.x Java驱动程序的示例：

DBCollection collection = mongoClient.getDB("stackoverflow").getCollection("demo");

BasicDBObject filter = new BasicDBObject();
BasicDBObject projection = new BasicDBObject();

// project on "Project_Information.Project_Description"
projection.put("Project_Information.Project_Description", 1);

DBCursor documents = collection.find(filter, projection);

for (DBObject document : documents) {
    // the response contains a sub document under the key: "Project_Information"
    DBObject projectInformation = (DBObject) document.get("Project_Information");
    // the "Project_Description" is in this sub document
    String projectDescription = (String) projectInformation.get("Project_Description");

    // prints "Sample"
    System.out.println(projectDescription);

    // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
    Object[] r = new Object[] {projectDescription};

    // prints the entire projected document e.g. 
    // { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
    System.out.println(document.toString());
}

    // this finds all documents in a given collection (note: no parameter supplied to the find() call) 
    // and for each document it projects on Project_Information.Project_Description
    FindIterable<Document> documents =
            mongoClient.getDatabase("...").getCollection("...")
               .find()
               // for each attrbute you want to project you must include its dot notation path and the value 1 ... 
               // this is the equivalent of specifying {'Project_Information.Project_Description': 1} in the MongoDB shell
               .projection(new Document("Project_Information.Project_Description", 1));

    for (Document document : documents) {
        // the response contains a sub document under the key: "Project_Information"
        Document projectInformation = (Document) document.get("Project_Information");
        // the "Project_Description" is in this sub document
        String projectDescription = projectInformation.getString("Project_Description");

        // prints "Sample"
        System.out.println(projectDescription);

        // to return this single String value in an Object[] (as implied by your OP) just do create the Object[] like this and then return it ...
        Object[] r = new Object[] {projectDescription};

        // prints the entire projected document e.g. { "_id" : { "$oid" : "59db2321811a592384865711" }, "Project_Information" : { "Project_Description" : "Sample" } }
        System.out.println(document.toJson());
    }

//这将查找给定集合中的所有文档（注意：没有为find（）调用提供参数）
//对于每个it项目的文档，请参见项目信息。项目描述
可查找文件=
mongoClient.getDatabase（“…”）.getCollection（“…”）
.find（）
//对于要投影的每个属性，必须包含其点表示法路径和值1。。。
//这相当于在MongoDB shell中指定{'Project_Information.Project_Description'：1}
.项目（新文件（“项目信息.项目说明”，1））；
用于（文档：文档）{
//响应包含一个子文档，位于“项目信息”项下
文档项目信息=（文档）Document.get（“项目信息”）；
//“项目描述”在本子文件中
String projectDescription=projectInformation.getString（“项目描述”）；
//打印“样本”
System.out.println（项目描述）；
//要在对象[]中返回此单个字符串值（如OP所示），只需像这样创建对象[]，然后返回它。。。
对象[]r=新对象[]{projectDescription}；
//打印整个投影文档，例如{“\u id”：{“$oid”：“59db221811a592384865711”}，“项目信息”：{“项目描述”：“示例”}
System.out.println（document.toJson（））；
}
-1因为您没有包含任何尝试过的代码。怎么