如何使用MockMvc测试具有流式内容的控制器？

Question

I'd like to test a Spring controller, without Spring context, with MockMvc . This controller streams the content by writing it in the OutputStream of the response.

Here is the controller code:

@RequestMapping(method = GET, value = "/file")
public void getFile(HttpServletResponse response) throws IOException {
    response.setHeader("Content-Disposition", "attachment; filename=file.json");
    ObjectWriter objectWriter = new ObjectMapper().setSerializationInclusion(JsonInclude.Include.NON_NULL).writer();

    Item item = new Item();
    List<Item> items = new ArrayList<>();
    items.add(item);

    try (Writer bufferedWriter = new BufferedWriter(new OutputStreamWriter(response.getOutputStream()))) {
        objectWriter.writeValue(bufferedWriter, items);
        bufferedWriter.flush();
    }
}

Here is the test:

@Test
public void getFile_ok() throws Exception {
    mockMvc.perform(get(END_POINT + "/file").accept(MediaType.APPLICATION_JSON))
           .andExpect(status().isOk());
}

This controller works well, but the unit test fails with an IOException:

java.io.IOException: Stream closed
    at java.io.BufferedWriter.ensureOpen(BufferedWriter.java:116)
    at java.io.BufferedWriter.flushBuffer(BufferedWriter.java:126)
    at java.io.BufferedWriter.flush(BufferedWriter.java:253)

Answer 1

Actually the objectWriter.writeValue(bufferedWriter, items); tries to close the stream.

Javadoc:

Note: method does not close the underlying stream explicitly here; however, JsonFactory this mapper uses may choose to close the stream depending on its settings (by default, it will try to close it when JsonGenerator we construct is closed).

In runtime, it doesn't close it but in my tests, it does, and the next line bufferedWriter.flush(); just sends the IOEception .

So to fix it I added a try/catch this way:

try {
    writer.flush();
} catch (IOException e) {
    logger.info("Stream closed in writeValue()", e);
}