java lambda使用

jdk8+以上引入了箭头函数，即J8的lambda表达式。

Lambda表达式的本质只是一个"语法糖",由编译器推断并帮你转换包装为常规的代码,因此你可以使用更少的代码来实现同样的功能。

在阅读jdbctemplate源码时候，看到一段这样的代码

return updateCount(execute(psc, ps -> {
//箭头函数，这里执行了回调功能
			try {
				if (pss != null) {
					pss.setValues(ps);
				}
				int rows = ps.executeUpdate();
				if (logger.isTraceEnabled()) {
					logger.trace("SQL update affected " + rows + " rows");
				}
				return rows;
			}
			finally {
				if (pss instanceof ParameterDisposer) {
					((ParameterDisposer) pss).cleanupParameters();
				}
			}
		}));

　继续看execute

@Override
	@Nullable
	public <T> T execute(PreparedStatementCreator psc, PreparedStatementCallback<T> action)
			throws DataAccessException {

		Assert.notNull(psc, "PreparedStatementCreator must not be null");
		Assert.notNull(action, "Callback object must not be null");
		if (logger.isDebugEnabled()) {
			String sql = getSql(psc);
			logger.debug("Executing prepared SQL statement" + (sql != null ? " [" + sql + "]" : ""));
		}

		Connection con = DataSourceUtils.getConnection(obtainDataSource());
		PreparedStatement ps = null;
		try {
			ps = psc.createPreparedStatement(con);
			applyStatementSettings(ps);
			T result = action.doInPreparedStatement(ps);
			handleWarnings(ps);
			return result;
		}
		catch (SQLException ex) {
			// Release Connection early, to avoid potential connection pool deadlock
			// in the case when the exception translator hasn't been initialized yet.
			if (psc instanceof ParameterDisposer) {
				((ParameterDisposer) psc).cleanupParameters();
			}
			String sql = getSql(psc);
			psc = null;
			JdbcUtils.closeStatement(ps);
			ps = null;
			DataSourceUtils.releaseConnection(con, getDataSource());
			con = null;
			throw translateException("PreparedStatementCallback", sql, ex);
		}
		finally {
			if (psc instanceof ParameterDisposer) {
				((ParameterDisposer) psc).cleanupParameters();
			}
			JdbcUtils.closeStatement(ps);
			DataSourceUtils.releaseConnection(con, getDataSource());
		}
	}

　上述代码是通过lambda进行回调操作，PreparedStatementCallback是接口，同时只有单实现

满足条件：

1、基于接口的回调

2、接口只能是单实现

下边是我们基于上述回调机制进行的代码实现：

接口：TestLambda

public interface TestLambda {
    public void prints(String str);
}

基于接口进行回调操作，lambda和非lambda实现

public class TestMain {
    public static void main(String[] args) {
        test(new TestLambda() {
            @Override
            public void prints(String str) {
                System.out.println("hello:"+str);
            }
        });


        test(str->{
            System.out.println("ni:"+str);
        });
    }


    public static void test(TestLambda tl){
        tl.prints("11111");
    }
}