…但是我希望图书馆尽其所能。

好吧，只需使用Gson。

有数据传输对象模式，尤其是Gson映射类，可以完美地解决您的问题。默认情况下，如果Gson能够满足内置功能的映射，并且除了特殊情况外，您不必自己完成工作。此类映射类仅旨在存在于JSON内容和您的业务对象类之间，以便对数据进行（反）序列化（简单地说，DTO仅为此目的而存在，并且与Gson相关的注释不得散布到您的业务类中-
只需将DTO转换为业务对象）。

对应

final class Wrapper {

    @SerializedName("id")
    @Expose
    private final String id = null;

    @SerializedName("games")
    @Expose
    private final List<String> games = null;

    @SerializedName("definition")
    @Expose
    private final FormulaDefinition formulaDefinition = null;

    private Wrapper() {
    }

    @Override
    public String toString() {
        return new StringBuilder("Wrapper{")
                .append("id='").append(id)
                .append("', games=").append(games)
                .append(", formulaDefinition=").append(formulaDefinition)
                .append('}')
                .toString();
    }

}



package q41323887;

import java.util.List;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

final class FormulaDefinition {

    @SerializedName("count")
    @Expose
    private /*final*/ int count /*= 0*/; // Gson works with final primitives like `int` strangely

    @SerializedName("operatorDefinitions")
    @Expose
    private final List<OperatorDefinition> operatorDefinitions = null;

    private FormulaDefinition() {
    }

    @Override
    public String toString() {
        return new StringBuilder("FormulaDefinition{")
                .append("count=").append(count)
                .append(", operatorDefinitions=").append(operatorDefinitions)
                .append('}')
                .toString();
    }

}



final class OperatorDefinition {

    @SerializedName("operators")
    @Expose
    private final Operator operators = null;

    @SerializedName("first")
    @Expose
    private final String first = null;

    @SerializedName("second")
    @Expose
    private final String second = null;

    @SerializedName("result")
    @Expose
    private final String result = null;

    private OperatorDefinition() {
    }

    @Override
    public String toString() {
        return new StringBuilder("OperatorDefinition{")
                .append("operators=").append(operators)
                .append(", first='").append(first)
                .append("', second='").append(second)
                .append("', result='").append(result)
                .append("'}")
                .toString();
    }

}



enum Operator {

    PLUS("+"),
    MINUS("-"),
    ASTERISK("*"),
    SLASH("/");

    private static final Map<String, Operator> tokenToOperatorIndex = createTokenToOperatorIndexInJava8();

    private final String token;

    Operator(final String token) {
        this.token = token;
    }

    static Operator resolveOperator(final String token)
            throws NoSuchElementException {
        final Operator operator = tokenToOperatorIndex.get(token);
        if ( operator == null ) {
            throw new NoSuchElementException("Cannot resolve operator by " + token);
        }
        return operator;
    }

    private static Map<String, Operator> createTokenToOperatorIndex() {
        final Map<String, Operator> index = new HashMap<>();
        for ( final Operator operator : values() ) {
            index.put(operator.token, operator);
        }
        return unmodifiableMap(index);
    }

    private static Map<String, Operator> createTokenToOperatorIndexInJava8() {
        final Map<String, Operator> index = Stream.of(values())
                .collect(toMap(operator -> operator.token, identity()));
        return unmodifiableMap(index);
    }

}

反序列化

然后，由于您本operators打算成为有效的枚举，因此这是您真正需要自定义JSON反序列化器的唯一地方，仅因为Gson默认规则不了解这些规则。

final class OperatorJsonDeserializer
        implements JsonDeserializer<Operator> {

    private static final JsonDeserializer<Operator> operatorJsonDeserializer = new OperatorJsonDeserializer();

    private OperatorJsonDeserializer() {
    }

    static JsonDeserializer<Operator> getOperatorJsonDeserializer() {
        return operatorJsonDeserializer;
    }

    @Override
    public Operator deserialize(final JsonElement json, final Type type, final JsonDeserializationContext context)
            throws JsonParseException {
        try {
            final String token = json.getAsJsonPrimitive().getAsString();
            return resolveOperator(token);
        } catch ( final NoSuchElementException ex ) {
            throw new JsonParseException(ex);
        }
    }

}

演示版

现在，您可以使用Wrapper该类反序列化JSON：

// Gson instances are thread-safe and can be easily instantiated once
private static final Gson gson = new GsonBuilder()
        .registerTypeAdapter(Operator.class, getOperatorJsonDeserializer())
        .create();

public static void main(final String... args)
        throws IOException {
    try ( final Reader reader = new InputStreamReader(EntryPoint.class.getResourceAsStream("/test.json")) ) {
        final Wrapper wrapper = gson.fromJson(reader, Wrapper.class);
        out.println(wrapper);
        // ... convert the wrapper DTO above to your target business object
    }
}

输出：

包装器{id = ‘10’，游戏= [PZ]，FormulaDefinition = FormulaDefinition {count =
10，operatorDefinitions = [OperatorDefinition {operators = PLUS，first
=‘1-5’，second =‘1-5’，result =’ 2-5’}]}}

编辑

我在以下代码片段中对Gson的理解是错误的：

    @SerializedName("count")
    @Expose
    private /*final*/ int count /*= 0*/; // Gson works with final primitives like `int` strangely

实际上，Gson 确实
工作正常。我忘记了Java常量内联。使用获得count通孔反射Field效果完美。但是，由于内联，返回了contant值。与相似的普通对象javap -p -c：

final class ext.Test$Immutable {
  private final int foo;

  private ext.Test$Immutable();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: aload_0
       5: iconst_0
       6: putfield      #2                  // Field foo:I
       9: return

  private int getFoo();
    Code:
       0: iconst_0
       1: ireturn

  public java.lang.String toString();
    Code:
       0: ldc           #4                  // String (IMMUTABLE:0)
       2: areturn
}

在这种情况下，甚至toString()返回一个常数。是的，这就是Java和javac工作方式。为了禁用这种内联并将final修饰符添加到该字段，就像周围的所有字段一样，应添加一个非编译时值：

    @SerializedName("count")
    @Expose
    private final int count = constOf(0);

哪里constOf(int)仅仅是：

private static int constOf(final int value) {
    return value;
}

现在，所有传入的DTO字段都可以轻松声明final。