CODEWITHSUNDEEP
javalambda
vamsi vegi
vamsi vegi

Reputation: 116

How to print to console in lambda call in Java 8

I am trying to print to system console within a lambda call, but it does not show in the output window (both within IDE and when run as mvn test)

Here is the code

public List<FieldDto> findField(String fieldKey) {
    jdbcTemplate.setQueryTimeout(10);
    System.out.println("\n\n\n\n ----------- seeeee  ----------------------");
    List<FieldDto> result = jdbcTemplate.query("select * from V_FIELD where FIELD_KEY = '" + fieldKey + "'",
            (rs, rowNum) -> getFieldDto(rs, rowNum)
    );
    System.out.println("\n\n\n\n ----------- done  ----------------------");
    return result;

}

and the method getFieldDto is defined as

private FieldDto getFieldDto(ResultSet rs, int rowNum) throws SQLException {
    FieldDto fieldDto = new FieldDto();
    System.out.println(" .. in getFieldDto:");
    try {
        fieldDto.FIELD_KEY = rs.getString("FIELD_KEY");
        fieldDto.CREATE_DATE = rs.getString("CREATE_DATE");

    } catch (Exception ex) {
        System.out.println(" exception getFieldDto:" + ex.getMessage());
        throw new RuntimeException(ex);
    }
    return fieldDto;
}

when I run the jUnit test, the console does show the ---see--- and ----done---, console logs, but not the '.. in getFieldDto'

why is that not happening, how can I print within the Lambda calls

Upvotes: 1

Views: 887

Answers (1)

Code-Apprentice
Code-Apprentice

Reputation: 83587

A lambda expression creates an instance of an anonymous inner class with a single method. The method is not called at the time of creation. Instead, it is called at some later point as a callback.

I believe you want to call the method immediately and pass the results as a parameter. So do exactly that! Do not wrap the call in a lambda expression:

List<FieldDto> result = jdbcTemplate.query("select * from V_FIELD where FIELD_KEY = '" + fieldKey + "'",
         getFieldDto(rs, rowNum));

Additionally, you should be very wary about concatenating strings to create a SQL query. This possibly leaves your app open to a SQL injection attack if you concatenate a String whose value comes from user input. Instead, you should use syntax like FIELD_KEY = ? in your query and the appropriate JDBC call which provides the parameters for the ? placeholder. JDBC will then clean all input to reduce the risk of an attack.

Upvotes: 2

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