java - 如何正确且线程安全地重用Jackson ObjectReader？

Question

Jackson 有 ObjectReader，文档说您需要使用它来保证线程安全。但我不明白如何正确地做到这一点

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;

import java.io.IOException;
import java.util.Map;

public class JsonParser {
    private ObjectMapper OBJECT_MAPPER = new ObjectMapper();
    private ObjectReader OBJECT_READER = new ObjectMapper().readerFor(Map.class);

    public Map<String, String> parseJson1(String json) throws IOException {
        ObjectReader objectReader = OBJECT_MAPPER.readerFor(Map.class);
        return objectReader.readValue(json);
    }

    public Map<String, String> parseJson2(String json) throws IOException {
        return OBJECT_READER.readValue(json);
    }
}

我写了两个示例

1. parseJson1() - 在每次解析时从 ObjectMapper 创建 ObjectReader
2. parseJson2() - 在 ObjectReader 上重用单个实例

哪一个是正确的？

Answer 1

文档说它是“完全线程安全的”，这意味着您可以安全地使用 parseJson2 而不必担心在并发线程中调用此方法。

https://fasterxml.github.io/jackson-databind/javadoc/2.5/com/fasterxml/jackson/databind/ObjectReader.html

Uses "fluent" (or, kind of, builder) pattern so that instances are immutable (and thus fully thread-safe with no external synchronization); new instances are constructed for different configurations. Instances are initially constructed by ObjectMapper and can be reused, shared, cached; both because of thread-safety and because instances are relatively light-weight.