[Bug]: ctx.map returns MapResult items as LinkedHashMap instead of the declared result type

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@pcbeingused333 已经在做这个了。

开始于 2026年11月3日。

  • #874 来自 @pcbeingused333 —— 未关闭

评估

难度
3/5
预计耗时
1-2 天
新手友好度
35/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
停滞
技术栈
aws, java
领域
backend

调研方向

Read sdk/src/main/java/software/amazon/lambda/durable/operation/MapOperation.java and trace how itemResultType reaches the serialized MapResult. Start with the existing MapIntegrationTest cases and add coverage for a POJO item on first execution and replay. Done means both paths return items as the declared type; an open pull request is already linked to this issue.

由索引模型根据 Issue 内容生成。

描述

bug pkg:sdk
Expected Behavior

DurableContext.map(name, items, Class<O>, fn, config) returns a MapResult<O> whose items are instances of O. This holds on the first execution and on replay.

Actual Behavior

When O is a POJO or record, each item in the returned MapResult is a java.util.LinkedHashMap. Reading an item as O throws ClassCastException.

This happens on the first execution, not only on replay. On completion, MapOperation replaces its result with a serialize-then-deserialize copy, so the first execution returns the same value that replay returns.

Steps to Reproduce
public record Payload(String value) {}

@Test
void itemIsDeclaredType() {
    var runner = LocalDurableTestRunner.create(String.class, (input, context) -> {
        var result = context.map(
                "m",
                List.of("a", "b"),
                Payload.class,
                (item, index, ctx) -> new Payload(item),
                MapConfig.builder().build());
        Object first = result.getResult(0);
        return first.getClass().getName();
    });
    var result = runner.runUntilComplete("x");
    assertEquals(ExecutionStatus.SUCCEEDED, result.getStatus());
    assertEquals(Payload.class.getName(), result.getResult(String.class));
}

The test fails:

expected: <...$Payload> but was: <java.util.LinkedHashMap>
SDK Version

main at 3.0.1-SNAPSHOT. Also reported on 2.x. On 1.2.1 the first execution returns Payload, and replay of a completed map returns LinkedHashMap.

Java Version

17

Is this a regression?

Yes

Last Working Version

None fully. 1.2.1 is correct on the first execution and wrong on replay.

Additional Context

The cause is in MapOperation. The constructor passes new TypeToken<>() {} to its superclass as the result type (sdk/src/main/java/software/amazon/lambda/durable/operation/MapOperation.java, line 83).

  1. That anonymous class is created inside the generic class MapOperation<I, O>.
  2. So the captured type is MapResult<O>, with O still a type variable.
  3. So Jackson has no item type and deserializes each item as a LinkedHashMap.
  4. The constructor receives the caller's TypeToken<O> as itemResultType. It stores it but does not use it to build the result type.

The existing MapIntegrationTest cases use String and Integer items. Jackson deserializes those correctly without type information, so the tests do not catch the bug.

The JavaScript SDK also returns the serdes round-trip of the batch result on both paths. Its items are plain JSON objects, which already match the declared TypeScript type. So keeping the round-trip and fixing the item type keeps Java consistent with JavaScript.

Suggested fix: build a parameterized MapResult<O> type from itemResultType, for example by letting TypeToken be created from a java.lang.reflect.Type. Add integration tests with a POJO item type for the first execution and for replay.

主要语言
Java
星标
28
派生
18
平均合并
16 小时 53 分钟
30 天内合并 PR
63

环境准备

从这里开始

  1. 先读完整个 Issue，再读项目的贡献指南。
  2. 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
  3. Fork 仓库，在一个分支上完成修改。
  4. 提交 Pull Request，并在描述里引用这个 Issue 编号。

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