feat(Status): Add a method to create a Status instance from an intege…

…r code

problem/pom.xml

@@ -43,6 +43,12 @@
             <version>${junit-jupiter.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.hamcrest</groupId>
             <artifactId>java-hamcrest</artifactId>

problem/src/main/java/org/zalando/problem/Status.java

@@ -4,6 +4,9 @@
 
 import javax.annotation.Nonnull;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 /**
@@ -263,11 +266,36 @@ public enum Status implements StatusType {
     private final int code;
     private final String reason;
 
+    // Build a HashMap of all status keyed by their codes.
+    // Used in the `ofCode` factory method
+    private static Map<Integer, Status> allStatusByCode = new HashMap<>();
+    static {
+        for (Status s : Status.values()) {
+            allStatusByCode.put(s.getStatusCode(), s);
+        }
+    }
+
     Status(final int statusCode, final String reasonPhrase) {
         this.code = statusCode;
         this.reason = reasonPhrase;
     }
 
+    /**
+     * Creates a Status instance from the given code.
+     *
+     * @param code the HTTP code as a number
+     * @return the correct enum value for this status code.
+     * @throws IllegalArgumentException if the given code does not correspond to a known HTTP status.
+     */
+    public static Status ofCode(Integer code) {
+        if (allStatusByCode.containsKey(code)) {
+            return allStatusByCode.get(code);
+        }
+        else {
+            throw new IllegalArgumentException("There is no known status for this code (" + code.toString() + ").");
+        }
+    }
+
     /**
      * Get the associated status code.
      *

problem/src/test/java/org/zalando/problem/StatusTest.java

@@ -1,6 +1,9 @@
 package org.zalando.problem;
 
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 import java.util.stream.Stream;
 
@@ -26,4 +29,25 @@ void shouldHaveMeaningfulToString() {
 
         assertThat(notFound.toString(), equalTo("404 Not Found"));
     }
+
+    @ParameterizedTest
+    @CsvSource({
+            "409, Conflict",
+            "404, Not Found",
+            "200, OK",
+            "500, Internal Server Error"
+    })
+    void shouldHaveCorrectValueFromCode(int code, String line) {
+        Status statusFromCode = Status.ofCode(code);
+
+        assertThat(statusFromCode.getStatusCode(), equalTo(code));
+        assertThat(statusFromCode.getReasonPhrase(), equalTo(line));
+    }
+
+    @Test
+    void shouldThrowOnNonExistingCode() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> {
+            Status.ofCode(111);
+        });
+    }
 }