HashMap中的对象被覆盖-Java

Question

I would like to create an HashMap where the key is a string and the value is a List. All the values are taken from a Mysql table. The problem is that I have an HashMap where the key is the right one while the value is not the right one, because it is overwritten. In fact I have for all different keys the same list with the same content. This is the code:

public static HashMap<String,List<Table_token>> getHashMapFromTokenTable() throws SQLException, Exception{

DbAccess.initConnection();
List<Table_token> listFrom_token = new ArrayList();
HashMap<String,List<Table_token>> hMapIdPath = new HashMap<String,List<Table_token>>();

String query = "select * from token";
resultSet = getResultSetByQuery(query);

while(resultSet.next()){

    String token=resultSet.getString(3);
    String path=resultSet.getString(4);
    String word=resultSet.getString(5);
    String lemma=resultSet.getString(6);
    String postag=resultSet.getString(7);
    String isTerminal=resultSet.getString(8);
    Table_token t_token = new Table_token();
    t_token.setIdToken(token);
    t_token.setIdPath(path);
    t_token.setWord(word);
    t_token.setLemma(lemma);
    t_token.setPosTag(postag);
    t_token.setIsTerminal(isTerminal);
    listFrom_token.add(t_token);
    System.out.println("path "+path+" path2: "+token);
    int row = resultSet.getRow();

    if(resultSet.next()){
        if((resultSet.getString(4).compareTo(path)!=0)){    
            hMapIdPath.put(path, listFrom_token);
                listFrom_token.clear();
            }
        resultSet.absolute(row);

    }
    if(resultSet.isLast()){
        hMapIdPath.put(path, listFrom_token);
            listFrom_token.clear();
    }

}

DbAccess.closeConnection();

return hMapIdPath;

}

You can find an example of the content of the HashMap below:

key: p000000383 content: [t0000000000000019231, t0000000000000019232, t0000000000000019233]

key: p000000384 content: [t0000000000000019231, t0000000000000019232, t0000000000000019233]

The values that are in "content" are in the last rows in Mysql table for the same key.

    mysql> select * from token where idpath='p000003361';
+---------+------------+----------------------+------------+
| idDoc   | idSentence | idToken              | idPath     |
+---------+------------+----------------------+------------+
| d000095 | s000000048 | t0000000000000019231 | p000003361 |
| d000095 | s000000048 | t0000000000000019232 | p000003361 |
| d000095 | s000000048 | t0000000000000019233 | p000003361 |
+---------+------------+----------------------+------------+
3 rows in set (0.04 sec)

Answer 1

You need to allocate a new listFrom_token each time instead of clear() ing it. Replace this:

            listFrom_token.clear();

with:

            listFrom_token = new ArrayList<Table_token>();

Putting the list in the HashMap does not make a copy of the list. You are clearing and refilling the same list over and over.

Answer 2

Your data shows that idPath is not a primary key. That's what you need to be the key in the Map. Maybe you should make idToken the key in the Map - it's the only thing in your example that's unique.

Your other choice is to make the column name the key and give the values to the List. Then you'll have four keys, each with a List containing four values.