# 流式传输 JSON Lines { #stream-json-lines }

当你想以“流”的方式发送一系列数据时，可以使用 JSON Lines。

/// info | 信息

新增于 FastAPI 0.134.0。

///

## 什么是流 { #what-is-a-stream }

“流式传输”数据意味着你的应用会在整段数据全部准备好之前，就开始把每个数据项发送给客户端。

也就是说，它会先发送第一个数据项，客户端会接收并开始处理它，而此时你的应用可能还在生成下一个数据项。

```mermaid
sequenceDiagram
    participant App
    participant Client

    App->>App: Produce Item 1
    App->>Client: Send Item 1
    App->>App: Produce Item 2

    """
    lines: list[str] = []

    if comment is not None:
        for line in comment.splitlines():
            lines.append(f": {line}")

    if event is not None:
        lines.append(f"event: {event}")

    if data_str is not None:
        for line in data_str.splitlines():
            lines.append(f"data: {line}")

    if id is not None:

# Stream Data { #stream-data }

If you want to stream data that can be structured as JSON, you should [Stream JSON Lines](../tutorial/stream-json-lines.md).

But if you want to **stream pure binary data** or strings, here's how you can do it.

/// info

Added in FastAPI 0.134.0.

///

## Use Cases { #use-cases }

You could use this if you want to stream pure strings, for example directly from the output of an **AI LLM** service.

   *
   * <p>This method prioritizes convenience over performance: It reads the entire input into memory
   * immediately. To instead read and process lines individually, use an alternative like {@link
   * BufferedReader#lines()}.
   *
   * <p><b>Java 25+ users:</b> If the input is a {@link Reader}, you may prefer {@link
   * Reader#readAllLines()}. The two may have different performance characteristics for different

  }
}

/**
 * Reads lines from `IdnaMappingTable.txt`.
 *
 * Comment lines are either blank or start with a `#` character. Lines may also end with a comment.
 * All comments are ignored.
 *
 * Regular lines contain fields separated by semicolons.
 *
 * The first element on each line is a single hex code point (like 0041) or a hex code point range
 * (like 0030..0039).
 *

  @IgnoreJRERequirement
  public Stream<String> lines() throws IOException {
    BufferedReader reader = openBufferedStream();
    return reader.lines().onClose(() -> closeUnchecked(reader));
  }

  @IgnoreJRERequirement // helper for lines()
  /*
   * If we make these calls inline inside the lambda inside lines(), we get an Animal Sniffer error,

SSE is a standard for streaming data from the server to the client over HTTP.

Each event is a small text block with "fields" like `data`, `event`, `id`, and `retry`, separated by blank lines.

It looks like this:

```
data: {"name": "Portal Gun", "price": 999.99}

data: {"name": "Plumbus", "price": 32.99}

```

Remember how our app/file structure looks like:

<img src="/img/tutorial/bigger-applications/package.drawio.svg">

---

The two dots `..`, like in:

```Python
from ..dependencies import get_token_header
```

mean:

* Starting in the same package that this module (the file `app/routers/items.py`) lives in (the directory `app/routers/`)...

* Tests that form a cluster made up of multiple versions of Elasticsearch like
full cluster restart, rolling restarts, and mixed version tests
* Tests that test the Elasticsearch clients in "interesting" places like the
`wildfly` project.
* Tests that test Elasticsearch in funny configurations like with ingest
disabled
* Tests that need to do strange things like install plugins that thrown
uncaught `Throwable`s or add a shutdown hook

If you are streaming JSON Lines, follow the [Stream JSON Lines](../tutorial/stream-json-lines.md) tutorial.

///

### `FileResponse` { #fileresponse }

Asynchronously streams a file as the response.