معماری بهار سری -6. ماژول JDBC در بهار

src/com/yaruyng/jdbc/
├── core/
│   ├── JdbcTemplate.java
│   ├── RowMapper.java
│   ├── ResultSetExtractor.java
│   ├── StatementCallBack.java
│   ├── PreparedStatementCallBack.java
│   └── ArgumentPreparedStatementSetter.java
├── datasource/
└── pool/

public class JdbcTemplate {
  private DataSource dataSource;

  public Object query(StatementCallBack stmtCallBack) {
    Connection con = null;
    Statement stmt = null;
    try {
      con = dataSource.getConnection();
      stmt = con.createStatement();
      return stmtCallBack.doInStatement(stmt);
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      try {
        stmt.close();
        con.close();
      } catch (SQLException e) {
      }
    }
    return null;
  }

  public Object query(String sql, Object[] args,
                      PreparedStatementCallBack pstmtCallBack) {
    Connection con = null;
    PreparedStatement pstmt = null;
    try {
      con = dataSource.getConnection();
      pstmt = con.prepareStatement(sql);
      ArgumentPreparedStatementSetter setter =
        new ArgumentPreparedStatementSetter(args);
      setter.setValues(pstmt);
      return pstmtCallBack.doInPreparedStatement(pstmt);
    } catch (SQLException e) {
      throw new RuntimeException(e);
    } finally {
      try {
        pstmt.close();
        con.close();
      } catch (SQLException e) {
      }
    }
  }
}

public interface RowMapper<T> {
    T mapRow(ResultSet rs, int rowNum) throws SQLException;
}

public class UserRowMapper implements RowMapper<User> {
    @Override
    public User mapRow(ResultSet rs, int rowNum) throws SQLException {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        user.setEmail(rs.getString("email"));
        return user;
    }
}

public class ArgumentPreparedStatementSetter {
    private final Object[] args;

    public void setValues(PreparedStatement pstmt) throws SQLException {
        if (this.args != null) {
            for (int i = 0; i < this.args.length; i++) {
                Object arg = this.args[i];
                doSetValue(pstmt, i+1, arg);
            }
        }
    }

    private void doSetValue(PreparedStatement pstmt, 
            int parameterPosition, Object argValue) throws SQLException {
        if (argValue instanceof String) {
            pstmt.setString(parameterPosition, (String)argValue);
        }
        else if (argValue instanceof Integer) {
            pstmt.setInt(parameterPosition, (int)argValue);
        }
        else if (argValue instanceof java.util.Date) {
            pstmt.setDate(parameterPosition, 
                new java.sql.Date(((java.util.Date)argValue).getTime()));
        }
    }
}

public interface ResultSetExtractor<T> {
  T extractData(ResultSet rs) throws SQLException;
}

public class RowMapperResultSetExtractor<T> implements ResultSetExtractor<List<T>> {
    private final RowMapper<T> rowMapper;

    public RowMapperResultSetExtractor(RowMapper<T> rowMapper) {
        this.rowMapper = rowMapper;
    }

    @Override
    public List<T> extractData(ResultSet rs) throws SQLException {
        List<T> results = new ArrayList<>();
        int rowNum = 0;
        while (rs.next()) {
            results.add(rowMapper.mapRow(rs, ++rowNum));
        }
        return results;
    }
}

List<User> users = jdbcTemplate.query(
    "SELECT * FROM users WHERE age > ?",
    new Object[]{18},
    new UserRowMapper()
);

Object result = jdbcTemplate.query(new StatementCallBack() {
    @Override
    public Object doInStatement(Statement stmt) throws SQLException {
        ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM users");
        if (rs.next()) {
            return rs.getInt(1);
        }
        return 0;
    }
});

Object result = jdbcTemplate.query(
    "UPDATE users SET name = ? WHERE id = ?",
    new Object[]{"John", 1},
    new PreparedStatementCallBack() {
        @Override
        public Object doInPreparedStatement(PreparedStatement pstmt) 
                throws SQLException {
            return pstmt.executeUpdate();
        }
    }
);