Skip to main content

如何解析JSON输出

虽然一些模型提供商支持返回结构化输出的内置方法，但并非全部都支持。我们可以使用输出解析器来帮助用户通过提示指定任意的 JSON 模式，查询符合该模式的模型输出，最后将该模式解析为 JSON。

note

请注意，大语言模型是存在泄漏的抽象！您需要使用具有足够能力的 LLM 来生成格式良好的 JSON。

前提条件

本指南假定您已熟悉以下概念：

JsonOutputParser 是一个内建选项，用于提示并解析 JSON 输出。

Pick your chat model:

Install dependencies

tip

See this section for general instructions on installing integration packages.

yarn add @langchain/groq

Add environment variables

GROQ_API_KEY=your-api-key

Instantiate the model

import { ChatGroq } from "@langchain/groq";

const model = new ChatGroq({
  model: "llama-3.3-70b-versatile",
  temperature: 0
});
import { ChatOpenAI } from "@langchain/openai";
const model = new ChatOpenAI({
  model: "gpt-4o",
  temperature: 0,
});

import { JsonOutputParser } from "@langchain/core/output_parsers";
import { ChatPromptTemplate } from "@langchain/core/prompts";

// Define your desired data structure. Only used for typing the parser output.
interface Joke {
  setup: string;
  punchline: string;
}

// A query and format instructions used to prompt a language model.
const jokeQuery = "Tell me a joke.";
const formatInstructions =
  "Respond with a valid JSON object, containing two fields: 'setup' and 'punchline'.";

// Set up a parser + inject instructions into the prompt template.
const parser = new JsonOutputParser<Joke>();

const prompt = ChatPromptTemplate.fromTemplate(
  "Answer the user query.\n{format_instructions}\n{query}\n"
);

const partialedPrompt = await prompt.partial({
  format_instructions: formatInstructions,
});

const chain = partialedPrompt.pipe(model).pipe(parser);

await chain.invoke({ query: jokeQuery });
{
  setup: "Why don't scientists trust atoms?",
  punchline: "Because they make up everything!"
}

流式处理​

JsonOutputParser 还支持流式传输部分数据块。当模型以多个数据块的形式返回部分 JSON 输出时，这会非常有用。解析器会跟踪这些部分数据块，并在模型完成输出生成时返回最终的 JSON 输出。

for await (const s of await chain.stream({ query: jokeQuery })) {
  console.log(s);
}
{}
{ setup: "" }
{ setup: "Why" }
{ setup: "Why don't" }
{ setup: "Why don't scientists" }
{ setup: "Why don't scientists trust" }
{ setup: "Why don't scientists trust atoms" }
{ setup: "Why don't scientists trust atoms?", punchline: "" }
{ setup: "Why don't scientists trust atoms?", punchline: "Because" }
{
  setup: "Why don't scientists trust atoms?",
  punchline: "Because they"
}
{
  setup: "Why don't scientists trust atoms?",
  punchline: "Because they make"
}
{
  setup: "Why don't scientists trust atoms?",
  punchline: "Because they make up"
}
{
  setup: "Why don't scientists trust atoms?",
  punchline: "Because they make up everything"
}
{
  setup: "Why don't scientists trust atoms?",
  punchline: "Because they make up everything!"
}

下一步​

你现在已了解了一种提示模型返回结构化 JSON 的方法。接下来，请查看关于获取结构化输出的更全面指南，了解其他技术。

Was this page helpful?


You can also leave detailed feedback on GitHub.