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Gson Path Extensions

An extension library for Gson Path that adds validation that does not exist in the core Gson Path library. The library supports Android Support Library annotations (without including the dependency), but also includes the FloatRange, IntRange and Size for non-Android projects.

  • This library currently supports validation for @FloatRange, @IntRange, @StringDef and @IntDef.
  • The @EmptyToNull annotation bundled in the library will convert empty strings, arrays, collections or maps to null.
    • If the value marked with @EmptyToNull is also marked with a @NonNull (or similar) annotation, it will throw an exception.

FloatRange example

The following is an example of @FloatRange annotation validation.

Model

@AutoGsonAdapter
interface FloatModel extends BaseFloatModel {
    @FloatRange(from = 0, to = 5, fromInclusive = false, toInclusive = false)
    Float getValue();
}

Generated validation

// Gsonpath Extensions
if (value_value != null) {

    // Extension - 'FloatRange' Annotation
    if (value_value <= 0.0) {
        throw new com.google.gson.JsonParseException("Invalid 'from' range for value. Expected: '> 0.0', Found '" + value_value + "'");
    }
    if (value_value >= 5.0) {
        throw new com.google.gson.JsonParseException("Invalid 'to' range for value. Expected: '< 5.0', Found '" + value_value + "'");
    }
}

IntRange example

The following is an example of @IntRange annotation validation.

Model

@AutoGsonAdapter
interface IntModel extends BaseModel<Integer> {
    @IntRange(from = 0, to = 5)
    Integer getValue();
}

Generated validation

// Gsonpath Extensions
if (value_value != null) {
    // Extension - 'IntRange' Annotation
    if (value_value < 0) {
        throw new com.google.gson.JsonParseException("Invalid 'from' range for value. Expected: '>= 0', Found '" + value_value + "'");
    }
    if (value_value > 5) {
        throw new com.google.gson.JsonParseException("Invalid 'to' range for value. Expected: '<= 5', Found '" + value_value + "'");
    }
}

Size example

The following is an example of @Size annotation validation.

Model

@AutoGsonAdapter
interface ArrayModel extends BaseArrayModel {
    @Size(min = 0, max = 6, multiple = 2, value = 2)
    Integer[] getValue();
}

Generated validation

// Gsonpath Extensions
if (value_value != null) {
    // Extension - 'Size' Annotation
    if (value_value.length != 2) {
        throw new com.google.gson.JsonParseException("Invalid array length for field 'value'. Expected length: '2', actual length: '" + value_value.length + "'");
    }
    if (value_value.length < 0) {
        throw new com.google.gson.JsonParseException("Invalid array length for field 'value'. Expected minimum: '0', actual minimum: '" + value_value.length + "'");
    }
    if (value_value.length > 6) {
        throw new com.google.gson.JsonParseException("Invalid array length for field 'value'. Expected maximum: '6', actual maximum: '" + value_value.length + "'");
    }
    if (value_value.length % 2 != 0) {
        throw new com.google.gson.JsonParseException("Invalid array length for field 'value'. length of '" + value_value.length + "' is not a multiple of 2");
    }
}

IntDef example

The following is an example of @IntDef annotation validation.

Model

@AutoGsonAdapter
interface IntDefModel {
    @IntDefExample
    Integer getValue();
    
    @Retention(RetentionPolicy.SOURCE)
    @IntDef({VALUE_1, VALUE_2})
    @interface IntDefExample {
        int VALUE_1 = 1;
        int VALUE_2 = 2;
    }
}

Generated validation

// Gsonpath Extensions
if (value_value != null) {
    // Extension - 'Int Def' Annotation
    switch (value_value) {
        case 1:
        case 2:
            break;
        
        default:
            throw new com.google.gson.JsonParseException("Unexpected Int '" + value_value + "' for field 'value'");
    }
}

StringDef example

The following is an example of @StringDef annotation validation. Note that the switch statement reassigns the string value to the actual constant from the @StringDef annotation. This is to appease the support library linting rules in Android Studio.

Model

@AutoGsonAdapter
interface StringDefModel {
    @StringDefExample
    String getValue();
    
    @Retention(RetentionPolicy.SOURCE)
    @StringDef({VALUE_1, VALUE_2})
    @interface StringDefExample {
        String VALUE_1 = "1";
        String VALUE_2 = "2";
    }
}

Generated validation

// Gsonpath Extensions
if (value_value != null) {
    // Extension - 'String Def' Annotation
    switch (value_value) {
        case StringDefExample.VALUE_1:
            value_value = StringDefExample.VALUE_1;
            break;
        
        case StringDefExample.VALUE_2:
            value_value = StringDefExample.VALUE_2;
            break;
        
        default:
            throw new com.google.gson.JsonParseException("Unexpected String '" + value_value + "' for field 'value'");
    }
}

EmptyToNull example

The following is an example of @EmptyToNull annotation validation.

Model

@AutoGsonAdapter
interface StringDefModel {
    @EmptyToNull
    String getNullableString();
    
    @EmptyToNull
    String[] getNullableArray();
    
    @EmptyToNull
    Collection<String> getNullableCollection();
    
    @EmptyToNull
    Map<String, String> getNullableMap();
    
    @NonNull
    @EmptyToNull
    String getNonNullString();
    
    @NonNull
    @EmptyToNull
    String[] getNonNullArray();
    
    @NonNull
    @EmptyToNull
    Collection<String> getNonNullCollection();
    
    @NonNull
    @EmptyToNull
    Map<String, String> getNonNullMap();
}

Generated validation (paraphrased)

// Extension - 'EmptyToNull' Annotation
if (nullableString.trim().length() == 0) {
    nullableString = null;
}
if (nullableArray.length == 0) {
    nullableArray = null;
}
if (nullableCollection.size() == 0) {
    nullableCollection = null;
}
if (nullableMap.size() == 0) {
    nullableMap = null;
}
if (nonNullString.trim().length() == 0) {
    throw new com.google.gson.JsonParseException("JSON element 'nonNullString' cannot be blank");
}
if (nonNullArray.length == 0) {
    throw new com.google.gson.JsonParseException("JSON element 'nonNullArray' cannot be blank");
}
if (nonNullCollection.size() == 0) {
    throw new com.google.gson.JsonParseException("JSON element 'nonNullCollection' cannot be blank");
}
if (nonNullMap.size() == 0) {
    throw new com.google.gson.JsonParseException("JSON element 'nonNullMap' cannot be blank");
}

Download

This library is available on Maven, you can add it to your project using the following gradle dependencies:

apt 'net.lachlanmckee:gsonpath-extensions:1.1.0'