public static void addJar(StreamExecutionEnvironment env, URL jarUrl) {
        addJar(env, Collections.singletonList(jarUrl));
    }
@Test
    public void testAddJars() throws Exception {
        Configuration configuration = new Configuration();
        configuration.set(PipelineOptions.JARS, Collections.EMPTY_LIST);
        StreamExecutionEnvironment env =
                StreamExecutionEnvironment.createLocalEnvironment(configuration);

        FlinkEnvironmentUtils.addJar(
                env, Lists.newArrayList(new URL("file://a.jar"), new URL("file://a.jar")));
        List<String> expectedJars = Lists.newArrayList("file://a.jar");
        Assert.assertEquals(expectedJars, env.getConfiguration().get(PipelineOptions.JARS));

        FlinkEnvironmentUtils.addJar(
                env, Lists.newArrayList(new URL("file://b.jar"), new URL("file://a.jar")));
        expectedJars.add("file://b.jar");
        Assert.assertEquals(expectedJars, env.getConfiguration().get(PipelineOptions.JARS));
    }