如果JsonStr中缺少任何键/值，如何在从JsonStr转换为PojoClassObj时引发异常? [英] How to throw exception while converting from JsonStr to PojoClassObj if any key/value is missing in the JsonStr?
问题描述
我尝试使用@NotNull批注，但是没有用.如果JsonString中缺少任何字段，则给出null(String)或zero(int).但是我想要的是，如果在类中定义的JsonStr中缺少任何字段，则应该引发异常.
I tried using @NotNull annotation but it did not work. If any field is missing in the JsonString, it gives null(String) or zero(int). But what I want is if any field is missing in the JsonStr defined in the class should throw an exception.
添加:我的PojoClass可能具有对象引用或多级对象引用.我正在使用 Gson 将String转换为obj.
为了进一步说明，我在下面添加了我的代码:
Add: My PojoClass may have object reference or multilevel object reference. I am using Gson for the conversion of the String to obj.
for more clarification, I have added my code below:
JsonStr:
{
"name":"John",
"id":1,
"roll":100,
"c":{
"city":"Dhaka",
"school":"B. govt. School"
}
}
代码:
public class C {
private String city;
private String school;
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getSchool() {
return school;
}
public void setSchool(String school) {
this.school = school;
}
}
ClassB:
public class B {
private String name;
private int id;
@NotNull
private int roll;
private C c;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getRoll() {
return roll;
}
public void setRoll(int roll) {
this.roll = roll;
}
public C getC() {
return c;
}
public void setC(C c) {
this.c = c;
}
}
MainClass:
try {
B obj = new B();
String str = "{\"name\":\"John\",\"id\":1,\"c\":{\"city\":\"dhaka\",\"school\":\"school\"}}";
obj = gson.fromJson(str, B.class);
} catch (RuntimeException e) {
System.out.println("exception Message");
}
对于字段滚动，如果JsonStr中不存在该字段，则我使用@NotNull引发异常，但该字段给出0的值而不会引发任何异常.
For the field roll, I used @NotNull to throw an exception if that field is not present in the JsonStr but it gives 0 value without throwing any exception.
我该如何实现?
请不要说这是重复的，因为我已经看过以下问题:
Please don't say this is duplicate, because I have seen these questions:
-
什么是NullPointerException，如何解决它?
What is a NullPointerException, and how do I fix it?
推荐答案
@NotNull不是Gson的一部分，并且默认情况下它无法处理它(除非您自己添加支持).同样，可空性检查注释不应应用于原始字段，通常来说，这没有多大意义.另外，默认的int字段值为0，并且Gson不会检查是否从JSON文档中读取了特定的字段.但是，如果您满足以下条件，则可以轻松实现它:@NotNullis not a part of Gson, and it cannot handle it by default (unless you add support yourself). Also, nullability-check annotations should not be applied to primitives fields -- generally speaking it makes not much sense. Also, the defaultintfields values are0, and Gson does not check if a particular field was read from a JSON document. However, you can easily implement it if you:- 通过将原语
int更改为其可为空的包装器Integer; 来稍微更改您的映射
- 实现自定义的后处理验证类型适配器.
- slightly change your mapping by changing the primitive
intto its nullable wrapperInteger; - implement a custom post-processing validation type adapter.
例如，
final class Person { final String name = null; final int id = Integer.valueOf(0); // final primitive fields are inlined by javac @NotNull final Integer roll = null; @SerializedName("c") final Location location = null; }final class Location { final String city = null; final String school = null; }下一步就是创建您自己的类型适配器以检查可为空的字段.
The next step is just creating your own type adapter to check the nullable fields.
final class NotNullTypeAdapterFactory implements TypeAdapterFactory { // The type adapter factory holds no state, so no need to instantiate it multiple times private static final TypeAdapterFactory notNullTypeAdapterFactory = new NotNullTypeAdapterFactory(); private NotNullTypeAdapterFactory() { } static TypeAdapterFactory getNotNullTypeAdapterFactory() { return notNullTypeAdapterFactory; } @Override public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> typeToken) { final Collection<Field> notNullFields = getNotNullFields(typeToken.getRawType()); // If no @NotNull fields found, then just tell Gson to pick the next best type adapter if ( notNullFields.isEmpty() ) { return null; } // If there's at least one @NotNull field, get the original type adapter final TypeAdapter<T> delegateTypeAdapter = gson.getDelegateAdapter(this, typeToken); return new TypeAdapter<T>() { @Override public void write(final JsonWriter out, final T value) throws IOException { delegateTypeAdapter.write(out, value); } @Override public T read(final JsonReader in) throws IOException { try { // Read the value ... final T value = delegateTypeAdapter.read(in); // ... and make some post-processing for ( final Field f : notNullFields ) { if ( f.get(value) == null ) { throw new MalformedJsonException(f + " has no value"); } } return value; } catch ( final IllegalAccessException ex ) { throw new IOException(ex); } } }; } private static Collection<Field> getNotNullFields(final Class<?> clazz) { // Primitive types and java.lang.Object do not have @NotNull if ( clazz.isPrimitive() || clazz == Object.class ) { return emptyList(); } // Scan the whole hierarchy from the bottom subclass to the top superclass (except java.lang.Object we mentioned above) final Collection<Field> notNullFields = new ArrayList<>(); for ( Class<?> c = clazz; c != Object.class; c = c.getSuperclass() ) { for ( final Field f : c.getDeclaredFields() ) { if ( f.isAnnotationPresent(NotNull.class) ) { // Don't forget to make private fields accessible f.setAccessible(true); notNullFields.add(f); } } } return notNullFields; } }测试(使用一些Google Guava和自定义资源阅读器):
Test (uses some Google Guava and custom resource readers):
private static final Gson gson = new GsonBuilder() .registerTypeAdapterFactory(getNotNullTypeAdapterFactory()) .create(); public static void main(final String... args) throws IOException { for ( final String resourceName : ImmutableList.of("file-with-roll.json", "file-without-roll.json") ) { System.out.println("Deserializing " + resourceName); try ( final JsonReader jsonReader = getPackageResourceJsonReader(Q44362030.class, resourceName) ) { try { final Person person = gson.fromJson(jsonReader, Person.class); System.out.println(person.name + " " + person.roll); } catch ( final Exception ex ) { System.out.println("FAILED! " + ex.getMessage()); } } } }输出:
反序列化file-with-roll.json
约翰100
反序列化file-without-roll.json
失败的！ com.google.gson.stream.MalformedJsonException:最终java.lang.Integer q44362030.Person.roll没有值Deserializing file-with-roll.json
John 100
Deserializing file-without-roll.json
FAILED! com.google.gson.stream.MalformedJsonException: final java.lang.Integer q44362030.Person.roll has no value类似地，您可以创建另一个
TypeAdapter来自动检查所有字段，甚至不需要@NotNull，但这需要更复杂的实现.Similarly, you can create your another
TypeAdapterto check all fields automatically not even needing@NotNull, but this needs a more complicated implementation.这篇关于如果JsonStr中缺少任何键/值，如何在从JsonStr转换为PojoClassObj时引发异常?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
- 通过将原语
