[#7516] fix: Ensure that converting a string to a namespace validates all input (#7569)

### What changes were proposed in this pull request?

Valid input string for fromString in Namespace.java

### Why are the changes needed?
Ensure that converting a string to a namespace validates all input

Fix: #7516 

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

(Please test your changes, and provide instructions on how to test it:
add these tests
``` java
  @test
  public void testFromString() {
    Assertions.assertEquals(Namespace.empty(), Namespace.fromString(""));
    Assertions.assertEquals(Namespace.of("a", "b"), Namespace.fromString("a.b"));
    Assertions.assertEquals(Namespace.of("a"), Namespace.fromString("a"));
  }

  @test
  public void testFromStringInvalidArgs() {
    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString(null));
    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString(".a"));
    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString("a."));
    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString("a..b"));
  }
```

Co-authored-by: Jackeyzhe <[email protected]>
Co-authored-by: jackeyzhe <[email protected]>

Author: 3 people

api/src/main/java/org/apache/gravitino/Namespace.java

@@ -19,9 +19,11 @@
 package org.apache.gravitino;
 
 import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
 import com.google.errorprone.annotations.FormatMethod;
 import com.google.errorprone.annotations.FormatString;
 import java.util.Arrays;
+import org.apache.commons.lang3.StringUtils;
 import org.apache.gravitino.exceptions.IllegalNamespaceException;
 
 /**
@@ -72,8 +74,12 @@ public static Namespace of(String... levels) {
    * @return A namespace with the given levels
    */
   public static Namespace fromString(String namespace) {
-    // todo: escape the dots in the levels if needed
-    return new Namespace(namespace.split("\\."));
+    Preconditions.checkArgument(namespace != null, "Cannot create a namespace with null input");
+    Preconditions.checkArgument(!namespace.endsWith("."), "Cannot create a namespace end with dot");
+    if (StringUtils.isBlank(namespace)) {
+      return empty();
+    }
+    return Namespace.of(namespace.split("\\."));
   }
 
   private Namespace(String[] levels) {

api/src/test/java/org/apache/gravitino/TestNamespace.java

@@ -46,4 +46,19 @@ public void testCreateNamespace() {
     Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.of("a", null, "c"));
     Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.of("a", "", "c"));
   }
+
+  @Test
+  public void testFromString() {
+    Assertions.assertEquals(Namespace.empty(), Namespace.fromString(""));
+    Assertions.assertEquals(Namespace.of("a", "b"), Namespace.fromString("a.b"));
+    Assertions.assertEquals(Namespace.of("a"), Namespace.fromString("a"));
+  }
+
+  @Test
+  public void testFromStringInvalidArgs() {
+    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString(null));
+    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString(".a"));
+    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString("a."));
+    Assertions.assertThrows(IllegalArgumentException.class, () -> Namespace.fromString("a..b"));
+  }
 }