@Override
    @Nullable
    public <T> T query(final String sql, final ResultSetExtractor<T> rse) throws DataAccessException {
        Assert.notNull(sql, "SQL must not be null");
        Assert.notNull(rse, "ResultSetExtractor must not be null");
        if (logger.isDebugEnabled()) {
            logger.debug("Executing SQL query [" + sql + "]");
        }

        // Callback to execute the query.
        class QueryStatementCallback implements StatementCallback<T>, SqlProvider {
            @Override
            @Nullable
            public T doInStatement(Statement stmt) throws SQLException {
                ResultSet rs = null;
                try {
                    rs = stmt.executeQuery(sql);
                    return rse.extractData(rs);
                }
                finally {
                    JdbcUtils.closeResultSet(rs);
                }
            }
            @Override
            public String getSql() {
                return sql;
            }
        }

        return execute(new QueryStatementCallback(), true);
    }

package study.base.varscope;

@FunctionalInterface
public interface ISum {
    long sum();
}

/**
 * 测试方法内的变量作用域，类似于js的闭包
 */
public class TestVarScope {

    public void test() {
         //创建一个有1000个元素的数组，每个元素都是介于1~999之间的随机数
        int[] arr = new int[1000];
        Random random = new Random();
        for (int i = 0; i < 1000; i++) {
            arr[i] = random.nextInt(1,1000);
        }
        class SumClass implements  ISum {
            @Override
            public long sum() {
                //累加 arr
                long total = 0;
                for (int i : arr) {
                    total += i;
                }
                return total;
            }
        }

        SumClass sc=new SumClass();
        long total=sc.sum();
        System.out.println(total);
    }

    public static void main(String[] args) {
        TestVarScope testVarScope = new TestVarScope();
        testVarScope.test();
    }

}