java - 带有枚举的 CodecConfigurationException

Question

我正在尝试创建一个示例来演示 mongodb java 驱动程序 POJO 中的枚举支持。该示例失败并出现异常 CodecConfigurationException: Cannot find a public constructor for 'PType6_'

使用的mongodb java驱动版本是3.11

build.gradle

dependencies {
    /*other dependencies*/
    compile 'org.mongodb:mongodb-driver-sync:3.11.0'
    /*other dependencies*/
}

枚举类型 PType6_

public enum PType6_ {
    ONE,
    TWO,
    THREE;

    public static PType6_ random() {
        return PType6_.values()[getRandomNumber(PType6_.values().length)];
    }

持有枚举类型的 POJO PType7_

public class PType7_ {
    private int number;
    private PType6_ pType6_1;

    public PType7_ setNumber(int number) {
        this.number = number;
        return this;
    }

    public PType7_ setPType6_1(PType6_ pType6_1) {
        this.pType6_1 = pType6_1;
        return this;
    }

    public int getNumber() {
        return number;
    }

    public PType6_ getPType6_1() {
        return pType6_1;
    }

    @Override
    public String toString() {
        return "PType7_{number=" + number + ", pType6_1=" + pType6_1 + '}';
    }

    public static PType7_ random() {
        return new PType7_()
                .setNumber(getRandomNumber(1000))
                .setPType6_1(PType6_.random());
    }
}

CodecRegistryFactory CustomCodecRegistriesFactoryWithPOJO

public class CustomCodecRegistriesFactoryWithPOJOs {
    public static CodecRegistry getDefault() {
        return MongoClientSettings.getDefaultCodecRegistry();
    }

    public static CodecRegistry getDefaultWithPOJOs(final Class<?>... pojoClasses) {
        return CodecRegistries.fromRegistries(
                CodecRegistries.fromProviders(PojoCodecProvider.builder().register(pojoClasses).build()),
                getDefault()
        );
    }

    public static CodecRegistry getDefaultWithPOJOsAndConventions(final List<Convention> conventions, final Class<?>... pojoClasses) {
        return CodecRegistries.fromRegistries(
                CodecRegistries.fromProviders(PojoCodecProvider.builder().conventions(conventions).register(pojoClasses).build()),
                getDefault()
        );
    }
}

测试方法

    @Test
    public void demonstrate_POJO_default_enum_registeringEnumClass_throwsException() {
        final MongoClient mc = buildMongoClientWithCustomCodec(CustomCodecRegistriesFactoryWithPOJOs.getDefaultWithPOJOs(PType7_.class, PType6_.class));
        final MongoDatabase mdb = initRandomDatabase(mc);
        final String colName = "col";
        mdb.createCollection(colName);
        final MongoCollection<Document> colDocs = mdb.getCollection(colName);
        final MongoCollection<PType7_> colTyped = mdb.getCollection(colName, PType7_.class);

        printTitle("[Encoding] Inserting PType7_ POJO Object");
        for (int i = 0; i < 5; i++) {
            colTyped.insertOne(PType7_.random());
        }

        printTitle("Reading Collection Raw");
        printDocumentMongoCollection(colDocs);

        printTitle("[Decoding] Reading PType7_ POJO Objects As Strings");
        try {
            for (final PType7_ item : colTyped.find()) {
                out.println(item);
            }
        } catch (final CodecConfigurationException e) {
            e.printStackTrace(out);
        }
    }

尝试解码枚举PType6_时抛出错误

摘要我想要一个完整且有效的示例来演示如何利用 mongodb java 驱动程序 POJO 对枚举的支持。

引用:POJOs - Plain Old Java Objects | Enum support

Answer 1

似乎是当枚举类型类PType6_本身注册为POJO时抛出此异常。这会以某种方式禁用默认行为，从而阻止枚举被序列化。

以下测试方法有效

    @Test
    public void demonstrate_POJO_default_enum() {
        final MongoClient mc = buildMongoClientWithCustomCodec(CustomCodecRegistriesFactoryWithPOJOs.getDefaultWithPOJOs(PType7_.class));
        final MongoDatabase mdb = initRandomDatabase(mc);
        final String colName = "col";
        mdb.createCollection(colName);
        final MongoCollection<Document> colDocs = mdb.getCollection(colName);
        final MongoCollection<PType7_> colTyped = mdb.getCollection(colName, PType7_.class);

        printTitle("[Encoding] Inserting PType7_ POJO Object");
        for (int i = 0; i < 5; i++) {
            colTyped.insertOne(PType7_.random());
        }

        printTitle("Reading Collection Raw");
        printDocumentMongoCollection(colDocs);

        printTitle("[Decoding] Reading PType7_ POJO Objects As Strings");
        for (final PType7_ item : colTyped.find()) {
            out.println(item);
        }
    }

唯一的区别是工作测试方法没有提供枚举类作为 POJO。

这不起作用

    final MongoClient mc = buildMongoClientWithCustomCodec(CustomCodecRegistriesFactoryWithPOJOs.getDefaultWithPOJOs(PType7_.class, PType6_.class));

这有效

    final MongoClient mc = buildMongoClientWithCustomCodec(CustomCodecRegistriesFactoryWithPOJOs.getDefaultWithPOJOs(PType7_.class));

结论 枚举默认作为属性处理，不需要将它们添加为 POJO 类。将它们添加为 POJO 类会禁用所添加枚举类的默认行为。