使用Java将Java对象插入MongoDB集合
我试图使用Java将整个Java对象插入到MongoDB集合中。 我收到以下错误：
错误：
Exception in thread "main" java.lang.IllegalArgumentException: can't serialize class net.yogesh.test.Employee at org.bson.BSONEncoder._putObjectField(BSONEncoder.java:185) at org.bson.BSONEncoder.putObject(BSONEncoder.java:119) at org.bson.BSONEncoder.putObject(BSONEncoder.java:65) at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:176) at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:134) at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:129) at com.mongodb.DBCollection.save(DBCollection.java:418) at net.yogesh.test.test.main(test.java:31) Emplyoee.java（POJO）
package net.yogesh.test; import java.io.Serializable; public class Employee implements Serializable { private static final long serialVersionUID = 1L; private long no; private String name; public Employee() { } public long getNo() { return no; } public void setNo(long no) { this.no = no; } public String getName() { return name; } public void setName(String name) { this.name = name; } }
主方法类（test.java）
package net.yogesh.test; import java.net.UnknownHostException; import com.mongodb.BasicDBObject; import com.mongodb.DB; import com.mongodb.DBCollection; import com.mongodb.Mongo; import com.mongodb.MongoException; public class test { public static void main(String[] args) throws UnknownHostException, MongoException { Mongo mongo = new Mongo("localhost", 27017); DB db = mongo.getDB("test"); Employee employee = new Employee(); employee.setNo(1L); employee.setName("yogesh"); BasicDBObject basicDBObject = new BasicDBObject("Name", employee); DBCollection dbCollection = db.getCollection("NameColl"); dbCollection.save(basicDBObject); } }
谁能解释为什么我收到这个错误？
我有点困惑，为什么你认为这首先起作用。 有些东西需要知道如何将POJO映射到MongoDB文档。 目前你没有告诉系统的任何部分如何做到这一点。
您可以使用映射库（Morphia浮现）或使用ReflectionDBObject。 两种解决方案（前者比后者更好）允许您将POJO映射到MongoDB文档并返回。
临
您可以继续使用强类型对象
反对
有些人真的不喜欢：延伸
package foo; import com.mongodb.BasicDBObject;
package foo; import com.mongodb.BasicDBObject;
public class Employee extends BasicDBObject {
private static final long serialVersionUID = 2105061907470199595L; //should be something shorter as "name" like "n" //here just use name to conform your sample public static final String NAME = "name"; public static final String NO = "no"; public static final String COLLECTION_NAME = "employee"; public Long getNo() { return getLong(NO); } public void setNo(long no) { put(NO, no); } public String getName() { return getString(NAME); } public void setName(String name) { put(NAME, name); }
}
package foo; import java.net.UnknownHostException; import com.mongodb.DB; import com.mongodb.DBCollection; import com.mongodb.Mongo; import com.mongodb.MongoException;
package foo; import java.net.UnknownHostException; import com.mongodb.DB; import com.mongodb.DBCollection; import com.mongodb.Mongo; import com.mongodb.MongoException;
公共课测试{
public static void main(String[] args) throws UnknownHostException, MongoException { Mongo mongo = new Mongo("localhost", 27017); DB db = mongo.getDB("yeahMongo"); Employee employee = new Employee(); employee.setNo(1L); employee.setName("yogesh"); DBCollection employeeCollection = null ; employeeCollection = db.getCollection(Employee.COLLECTION_NAME); employeeCollection.save(employee); System.err.println(employeeCollection.findOne()); }
}
除了morphia，你应该看一下jongo： http ：//jongo.org/jongo使用与js mongo引擎相同的表单语法，我发现它对初学者来说很有意义。 您不必在mongojs和java之间切换思维导图。 你可以使用js样本，几乎没有变化。
DB db = mongoClient.getDB( "mydb" ); coll = db.getCollection("testCollection"); Employee emp = new Employee(); emp.setId("1001"); emp.setName("John Doe"); //Converting a custom Class(Employee) to BasicDBObject Gson gson = new Gson(); BasicDBObject obj = (BasicDBObject)JSON.parse(gson.toJson(emp)); coll.insert(obj); findEmployee(new BasicDBObject("id","1001")); public static void findEmployee(BasicDBObject query){ DBCursor cursor = coll.find(query); try { while(cursor.hasNext()) { DBObject dbobj = cursor.next(); //Converting BasicDBObject to a custom Class(Employee) Employee emp = (new Gson()).fromJson(dbobj.toString(), Employee.class); System.out.println(emp.getName()); } } finally { cursor.close(); } }
我认为发布以两种方式进行转换的代码会很有用。
存储员工对象
查找并重新创建员工对象
希望这很有用..
您可以使用gson库将java对象转换为json字符串，然后将其插入mongodb。
例如：
Gson gson = new Gson(); String json = gson.toJson(Employee); BasicDBObject basicDBObject = new BasicDBObject("Name", json ); DBCollection dbCollection = db.getCollection("NameColl"); dbCollection.save(basicDBObject);
使用MongoDB，您无法在数据库中插入Java bean，但必须将它们重新映射到MongoDB Object。
在你的情况下你必须这样做：
BasicDBObject basicDBObject = new BasicDBObject(); basicDBObject.put("no", employee.getNo()); basicDBObject.put("name", employee.getName());
自提出此问题以来，已经有一些变化。 在问题中使用test.java ，这是使用Google的Gson对我test.java的：
import com.google.gson.Gson; import com.mongodb.Block; import com.mongodb.MongoClient; import com.mongodb.client.FindIterable; import com.mongodb.client.MongoDatabase; import org.bson.Document; public class test { public static void main(String[] args) { MongoClient mongoClient = new MongoClient(); // Connect with default settings ie localhost:27017 MongoDatabase db = mongoClient.getDatabase("test"); // Get database "test". Creates one if it doesn't exist Employee employee = new Employee(); // Create java object employee.setNo(1L); employee.setName("yogesh"); // Deserialize object to json string Gson gson = new Gson(); String json = gson.toJson(employee); // Parse to bson document and insert Document doc = Document.parse(json); db.getCollection("NameColl").insertOne(doc); // Retrieve to ensure object was inserted FindIterable iterable = db.getCollection("NameColl").find(); iterable.forEach(new Block () { @Override public void apply(final Document document) { System.out.println(document); // See below to convert document back to Employee } }); } }
您还可以使用Gson将检索到的bson文档转换回Java对象：
Gson gson = new Gson(); Employee emp = gson.fromJson(document.toJson(), Employee.class);
可能你可以使用一些专门的对象文档映射框架API，如Moprphia
强烈推荐MongoJack ，一个将Java对象映射到MongoDB文档/从MongoDB文档映射的合适库。
代码如下所示：
import java.util.Arrays; import org.mongojack.JacksonDBCollection; import com.mongodb.DB; import com.mongodb.MongoClient; import com.mongodb.ServerAddress; public class Test { public static void main(String[] args) { MongoClient mongoClient = new MongoClient(Arrays.asList(new ServerAddress("localhost", 27017))); DB db = mongoClient.getDB("test"); Employee employee = new Employee(); employee.setNo(1L); employee.setName("yogesh"); JacksonDBCollection collectionData = JacksonDBCollection.wrap(db.getCollection("NameColl"), Employee.class, String.class); collectionData.save(employee); mongoClient.close(); } }
（PS：目前我正在使用mongo-java-driver v3.2.2和mongojack v2.6.1）
使用BasicDBObjectBuilder将POJO转换为DBCollection可以保存的DBObject实例：
import com.mongodb.BasicDBObjectBuilder; import com.mongodb.DBObject; public class Employee { private long no; private String name; // Getters and Setters public DBObject toDBObject() { BasicDBObjectBuilder builder = BasicDBObjectBuilder .start("no", no) .append("name", name); return builder.get(); } }
为了保存，只需在POJO实例上调用toDBObject()并将其提供给集合：
public class test { public static void main(String[] args) throws UnknownHostException, MongoException { ... DBCollection dbCollection = db.getCollection("NameColl"); Employee employee = new Employee(); employee.setNo(1L); employee.setName("yogesh"); dbCollection.save(employee.toDBObject()); } }
使用这种方法：
- 您不需要每次都手动创建
DBObject - 你不需要通过扩展Mongo类来搞乱你的POJO（如果你的POJO已经扩展了一个类怎么办？）
- 您不需要Json映射器[及其在POJO字段上的注释]
- 你只对java-mongo-driver jar有依赖
当我尝试将java BasicDBObject插入MongoDb集合时，我有同样的错误。
我的对象是从转换为Json的Xml创建的。
java.lang.IllegalArgumentException: can't serialize class net.sf.json.JSONNull at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:299) at org.bson.BasicBSONEncoder.putMap(BasicBSONEncoder.java:339) at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:261)
此错误是由Xml中的空标记引起的; 当我删除所有空标签时，我解决了它。
迟到但最新，Mongod 3.5以后可以直接插入bean。