CODEWITHSUNDEEP
javaspringlambdajdbctemplate
nwGCham
nwGCham

Reputation: 313

How to implement RowMapper using java lambda expression

I had a working RowMapper code that maps database table row in to a java object. I wanted to change the implementation using lambda expression. However, I am always getting error; Code snippet as follows;

String queryString = "select * from person where person_id = ? ";
RowMapper rowMapper = (rs, rowNum) -> {

Person p = new Person();

p.setName(rs.getString("personName"));
p.setAddress(rs.getString("address"));
p.setAge(rs.getInt("age"));
}

Person person = getJdbcTemplate().query(queryString, personId, rowMapper);

return person;

Can someone help me to implement code correctly? Any idea to get list of persons?

Upvotes: 18

Views: 33390

Answers (4)

Rahul Chauhan
Rahul Chauhan

Reputation: 1625

In addition to @Tunaki answer.

RowMapper<Person> rowMapper = (rs, rowNum) -> {
    Person p = new Person();
    p.setName(rs.getString("personName"));
    p.setAddress(rs.getString("address"));
    p.setAge(rs.getInt("age"));
    return p;
};

Map<String, Object> paramMap = new HashMap<>();
paramMap.put("person_id", personId);

If you want to get single Person : 

Person person = getJdbcTemplate().queryForObject(queryString, paramMap, rowMapper);

If you want to get List of Person :

List<Person> personList = getJdbcTemplate().query(queryString, paramMap, rowMapper);

Upvotes: 4

NuAlphaMan
NuAlphaMan

Reputation: 713

@Tunaki is correct. Here is the shorthand version:

RowMapper<Person> rowMapper = (rs, rowNum) -> new Person(rs.getString("personName"), rs.getString("address"),rs.getInt("age")) ;

The brackets and the return aren't needed as they are implied.

Upvotes: 4

Ferdous Wahid
Ferdous Wahid

Reputation: 3367

RowMapper using lambda expression example:

return jdbcTemplate.query(" select Scale_Point,Scale_Head from TEval_Scale ", new Object[] {},
                (resultSet, rowNum) ->{

                    TEvalScale tEvalScale = new TEvalScale();
                    tEvalScale.setScalePoint(resultSet.getInt("Scale_Point"));
                    tEvalScale.setScaleHead(resultSet.getString("Scale_Head"));
                    return tEvalScale;

                });

Upvotes: 5

Tunaki
Tunaki

Reputation: 137084

RowMapper is a interface with a single abstract method (not inheriting from a method of Object), so it can be considered a functional interface. Its functional method takes a ResultSet and a int, and returns an object.

The first problem with the code is that the type of the object returned is a generic type of the interface. As currently used with RowMapper, you're using a raw-type, which you shouldn't do. The second issue is that the lambda expression does not return any object, so it cannot conform to the functional method which except an object to be returned.

As such, a corrected code would be:

RowMapper<Person> rowMapper = (rs, rowNum) -> {
    Person p = new Person();
    p.setName(rs.getString("personName"));
    p.setAddress(rs.getString("address"));
    p.setAge(rs.getInt("age"));
    return p;
};

Upvotes: 26

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