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Introduce Parameter-based factory methods in TypeDescriptor #37015

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Introduce Parameter-based factory methods in TypeDescriptor #37015

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5b3063c
Introduce Parameter-based factory methods in TypeDescriptor
sunnyboy33 Jul 7, 2026
b8d8658
Add unit tests for Parameter-based TypeDescriptor factory methods
sunnyboy33 Jul 7, 2026
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39 changes: 39 additions & 0 deletions spring-core/src/main/java/org/springframework/core/convert/TypeDescriptor.java
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.Parameter;
import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.Collection;
Expand Down Expand Up @@ -548,6 +549,18 @@ public String toString() {
}


/**
* Create a new type descriptor for the specified {@link Parameter}.
* <p>This is a convenience factory method for scenarios where a {@code Parameter}
* descriptor is already available.
* @param parameter the source parameter
* @return the corresponding type descriptor
* @since 7.1
*/
public static TypeDescriptor forParameter(Parameter parameter) {
return new TypeDescriptor(MethodParameter.forParameter(parameter));
}

/**
* Create a new type descriptor for an object.
* <p>Use this factory method to introspect a source object before asking the
Expand Down Expand Up @@ -676,6 +689,32 @@ public static TypeDescriptor map(Class<?> mapType, @Nullable TypeDescriptor keyT
return new TypeDescriptor(methodParameter).nested(nestingLevel);
}

/**
* Create a type descriptor for a nested type declared within the parameter.
* <p>For example, if the parameter is a {@code List<String>} and the
* nesting level is 1, the nested type descriptor will be {@code String.class}.
* <p>If the parameter is a {@code List<List<String>>} and the nesting
* level is 2, the nested type descriptor will also be a {@code String.class}.
* <p>If the parameter is a {@code Map<Integer, String>} and the nesting
* level is 1, the nested type descriptor will be String, derived from the map value.
* <p>If the parameter is a {@code List<Map<Integer, String>>} and the
* nesting level is 2, the nested type descriptor will be String, derived from the map value.
* <p>Returns {@code null} if a nested type cannot be obtained because it was not declared.
* For example, if the parameter is a {@code List<?>}, the nested type
* descriptor returned will be {@code null}.
* @param parameter the parameter
* @param nestingLevel the nesting level of the collection/array element or
* map key/value declaration within the parameter
* @return the nested type descriptor at the specified nesting level,
* or {@code null} if it could not be obtained
* @throws IllegalArgumentException if the types up to the specified nesting
* level are not of collection, array, or map types
* @since 7.1
*/
public static @Nullable TypeDescriptor nested(Parameter parameter, int nestingLevel) {
return new TypeDescriptor(MethodParameter.forParameter(parameter)).nested(nestingLevel);
}

/**
* Create a type descriptor for a nested type declared within the field.
* <p>For example, if the field is a {@code List<String>} and the nesting
Expand Down
32 changes: 32 additions & 0 deletions spring-core/src/test/java/org/springframework/core/convert/TypeDescriptorTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
Expand Down Expand Up @@ -86,6 +88,36 @@ void parameterScalar() throws Exception {
assertThat(desc.isMap()).isFalse();
}

@Test
void forParameter() throws Exception {
Method method = getClass().getMethod("testParameterScalar", String.class);
Parameter parameter = method.getParameters()[0];
TypeDescriptor desc = TypeDescriptor.forParameter(parameter);
assertThat(desc.getType()).isEqualTo(String.class);
}

@Test
void forParameterMustNotBeNull() {
assertThatIllegalArgumentException()
.isThrownBy(() -> TypeDescriptor.forParameter(null))
.withMessage("Parameter must not be null");
}

@Test
void nestedParameter() throws Exception {
Method method = getClass().getMethod("test2", List.class);
Parameter parameter = method.getParameters()[0];
TypeDescriptor desc = TypeDescriptor.nested(parameter, 2);
assertThat(desc.getType()).isEqualTo(String.class);
}

@Test
void nestedParameterMustNotBeNull() {
assertThatIllegalArgumentException()
.isThrownBy(() -> TypeDescriptor.nested((Parameter) null, 2))
.withMessage("Parameter must not be null");
}

@Test
void parameterList() throws Exception {
MethodParameter methodParameter = new MethodParameter(getClass().getMethod("testParameterList", List.class), 0);
Expand Down