[#6496] feat(CLI): Support plain format output for Schema and Table command (#6497)

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

Support plain format output for Schema and Table command

### Why are the changes needed?

Fix: #6496

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

No

### How was this patch tested?

local test
```bash
gcli schema list -m demo_metalake --name Hive_catalog  -i
default,Default Hive database

gcli table list -m demo_metalake --name Hive_catalog.default -i 
employee_partitions
source_table
test_dt_partition
test_key_en
sales
order_tb1
tmp
float_test
test_tbl

gcli table details -m demo_metalake --name Hive_catalog.default.test1  -i 
test1,N/A

gcli schema details -m demo_metalake --name Hive_catalog.default -i 
default,Default Hive database
```

Author: Abyss-lord

clients/cli/src/main/java/org/apache/gravitino/cli/outputs/OutputFormat.java

@@ -26,7 +26,7 @@
  */
 public interface OutputFormat<T> {
   /** Joiner for creating comma-separated output strings, ignoring null values */
-  Joiner COMMA_JOINER = Joiner.on(", ").skipNulls();
+  Joiner COMMA_JOINER = Joiner.on(",").skipNulls();
   /** Joiner for creating line-separated output strings, ignoring null values */
   Joiner NEWLINE_JOINER = Joiner.on(System.lineSeparator()).skipNulls();
 

clients/cli/src/main/java/org/apache/gravitino/cli/outputs/PlainFormat.java

@@ -21,9 +21,12 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Collectors;
+import org.apache.gravitino.Audit;
 import org.apache.gravitino.Catalog;
 import org.apache.gravitino.Metalake;
+import org.apache.gravitino.Schema;
 import org.apache.gravitino.cli.CommandContext;
+import org.apache.gravitino.rel.Table;
 
 /** Plain format to print a pretty string to standard out. */
 public abstract class PlainFormat<T> extends BaseOutputFormat<T> {
@@ -45,6 +48,16 @@ public static void output(Object entity, CommandContext context) {
       new CatalogPlainFormat(context).output((Catalog) entity);
     } else if (entity instanceof Catalog[]) {
       new CatalogListPlainFormat(context).output((Catalog[]) entity);
+    } else if (entity instanceof Schema) {
+      new SchemaPlainFormat(context).output((Schema) entity);
+    } else if (entity instanceof Schema[]) {
+      new SchemaListPlainFormat(context).output((Schema[]) entity);
+    } else if (entity instanceof Table) {
+      new TablePlainFormat(context).output((Table) entity);
+    } else if (entity instanceof Table[]) {
+      new TableListPlainFormat(context).output((Table[]) entity);
+    } else if (entity instanceof Audit) {
+      new AuditPlainFormat(context).output((Audit) entity);
     } else {
       throw new IllegalArgumentException("Unsupported object type");
     }
@@ -124,14 +137,98 @@ public CatalogListPlainFormat(CommandContext context) {
     /** {@inheritDoc} */
     @Override
     public String getOutput(Catalog[] catalogs) {
-      if (catalogs == null || catalogs.length == 0) {
-        output("No catalogs exist.", System.out);
-        return null;
-      } else {
-        List<String> catalogNames =
-            Arrays.stream(catalogs).map(Catalog::name).collect(Collectors.toList());
-        return NEWLINE_JOINER.join(catalogNames);
-      }
+
+      List<String> catalogNames =
+          Arrays.stream(catalogs).map(Catalog::name).collect(Collectors.toList());
+      return NEWLINE_JOINER.join(catalogNames);
+    }
+  }
+
+  /**
+   * Formats a single {@link Schema} instance as a comma-separated string. Output format: name,
+   * comment
+   */
+  static final class SchemaPlainFormat extends PlainFormat<Schema> {
+    public SchemaPlainFormat(CommandContext context) {
+      super(context);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public String getOutput(Schema schema) {
+      return COMMA_JOINER.join(schema.name(), schema.comment());
+    }
+  }
+
+  /**
+   * Formats an array of Schemas, outputting one name per line. Returns null if the array is empty
+   * or null.
+   */
+  static final class SchemaListPlainFormat extends PlainFormat<Schema[]> {
+    public SchemaListPlainFormat(CommandContext context) {
+      super(context);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public String getOutput(Schema[] schemas) {
+      List<String> schemaNames =
+          Arrays.stream(schemas).map(Schema::name).collect(Collectors.toList());
+      return NEWLINE_JOINER.join(schemaNames);
+    }
+  }
+
+  /**
+   * Formats a single Table instance with detailed column information. Output format: table_name,
+   * table_comment
+   */
+  static final class TablePlainFormat extends PlainFormat<Table> {
+    public TablePlainFormat(CommandContext context) {
+      super(context);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public String getOutput(Table table) {
+      String comment = table.comment() == null ? "N/A" : table.comment();
+      return COMMA_JOINER.join(new String[] {table.name(), comment});
+    }
+  }
+
+  /**
+   * Formats an array of Tables, outputting one name per line. Returns null if the array is empty or
+   * null.
+   */
+  static final class TableListPlainFormat extends PlainFormat<Table[]> {
+    public TableListPlainFormat(CommandContext context) {
+      super(context);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public String getOutput(Table[] tables) {
+      List<String> tableNames = Arrays.stream(tables).map(Table::name).collect(Collectors.toList());
+      return NEWLINE_JOINER.join(tableNames);
+    }
+  }
+
+  /**
+   * Formats an instance of {@link Audit} , outputting the audit information. Output format:
+   * creator, create_time, modified, modified_time
+   */
+  static final class AuditPlainFormat extends PlainFormat<Audit> {
+    public AuditPlainFormat(CommandContext context) {
+      super(context);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public String getOutput(Audit audit) {
+      return COMMA_JOINER.join(
+          audit.creator(),
+          audit.createTime() == null ? "N/A" : audit.createTime(),
+          audit.lastModifier() == null ? "N/A" : audit.lastModifier(),
+          audit.lastModifiedTime() == null ? "N/A" : audit.lastModifiedTime());
     }
   }
 }

clients/cli/src/test/java/org/apache/gravitino/cli/output/TestPlainFormat.java

@@ -33,6 +33,9 @@
 import org.apache.gravitino.Schema;
 import org.apache.gravitino.cli.CommandContext;
 import org.apache.gravitino.cli.outputs.PlainFormat;
+import org.apache.gravitino.rel.Table;
+import org.apache.gravitino.rel.types.Type;
+import org.apache.gravitino.rel.types.Types;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
@@ -64,7 +67,7 @@ void testMetalakeDetailsWithPlainFormat() {
 
     PlainFormat.output(mockMetalake, mockContext);
     String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
-    Assertions.assertEquals("demo_metalake, This is a demo metalake", output);
+    Assertions.assertEquals("demo_metalake,This is a demo metalake", output);
   }
 
   @Test
@@ -85,8 +88,7 @@ void testCatalogDetailsWithPlainFormat() {
 
     PlainFormat.output(mockCatalog, mockContext);
     String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
-    Assertions.assertEquals(
-        "demo_catalog, RELATIONAL, demo_provider, This is a demo catalog", output);
+    Assertions.assertEquals("demo_catalog,RELATIONAL,demo_provider,This is a demo catalog", output);
   }
 
   @Test
@@ -102,6 +104,75 @@ void testListCatalogWithPlainFormat() {
     Assertions.assertEquals("catalog1\n" + "catalog2", output);
   }
 
+  @Test
+  void testSchemaDetailsWithPlainFormat() {
+    CommandContext mockContext = getMockContext();
+    Schema mockSchema = getMockSchema();
+    PlainFormat.output(mockSchema, mockContext);
+    String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
+    Assertions.assertEquals("demo_schema,This is a demo schema", output);
+  }
+
+  @Test
+  void testListSchemaWithPlainFormat() {
+    CommandContext mockContext = getMockContext();
+    Schema mockSchema1 = getMockSchema("schema1", "This is a schema");
+    Schema mockSchema2 = getMockSchema("schema2", "This is another schema");
+
+    PlainFormat.output(new Schema[] {mockSchema1, mockSchema2}, mockContext);
+    String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
+    Assertions.assertEquals("schema1\n" + "schema2", output);
+  }
+
+  @Test
+  void testTableDetailsWithPlainFormat() {
+    CommandContext mockContext = getMockContext();
+    Table mockTable = getMockTable();
+    PlainFormat.output(mockTable, mockContext);
+    String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
+    Assertions.assertEquals("demo_table,This is a demo table", output);
+  }
+
+  @Test
+  void testAuditWithTableFormat() {
+    CommandContext mockContext = getMockContext();
+    Audit mockAudit = mock(Audit.class);
+    when(mockAudit.creator()).thenReturn("demo_user");
+    when(mockAudit.createTime()).thenReturn(Instant.ofEpochMilli(1611111111111L));
+    when(mockAudit.lastModifier()).thenReturn("demo_user");
+    when(mockAudit.lastModifiedTime()).thenReturn(Instant.ofEpochMilli(1611111111111L));
+
+    PlainFormat.output(mockAudit, mockContext);
+    String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
+    Assertions.assertEquals(
+        "demo_user,2021-01-20T02:51:51.111Z,demo_user,2021-01-20T02:51:51.111Z", output);
+  }
+
+  @Test
+  void testAuditWithTableFormatWithNullValues() {
+    CommandContext mockContext = getMockContext();
+    Audit mockAudit = mock(Audit.class);
+    when(mockAudit.creator()).thenReturn("demo_user");
+    when(mockAudit.createTime()).thenReturn(null);
+    when(mockAudit.lastModifier()).thenReturn(null);
+    when(mockAudit.lastModifiedTime()).thenReturn(null);
+
+    PlainFormat.output(mockAudit, mockContext);
+    String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
+    Assertions.assertEquals("demo_user,N/A,N/A,N/A", output);
+  }
+
+  @Test
+  void testListTableWithPlainFormat() {
+    CommandContext mockContext = getMockContext();
+    Table mockTable1 = getMockTable("table1", "This is a table");
+    Table mockTable2 = getMockTable("table2", "This is another table");
+
+    PlainFormat.output(new Table[] {mockTable1, mockTable2}, mockContext);
+    String output = new String(outContent.toByteArray(), StandardCharsets.UTF_8).trim();
+    Assertions.assertEquals("table1\n" + "table2", output);
+  }
+
   @Test
   void testOutputWithUnsupportType() {
     CommandContext mockContext = getMockContext();
@@ -159,13 +230,35 @@ private Schema getMockSchema(String name, String comment) {
     return mockSchema;
   }
 
-  private Audit getMockAudit() {
-    Audit mockAudit = mock(Audit.class);
-    when(mockAudit.creator()).thenReturn("demo_user");
-    when(mockAudit.createTime()).thenReturn(Instant.ofEpochMilli(1611111111111L));
-    when(mockAudit.lastModifier()).thenReturn("demo_user");
-    when(mockAudit.lastModifiedTime()).thenReturn(Instant.ofEpochMilli(1611111111111L));
+  private Table getMockTable() {
+    return getMockTable("demo_table", "This is a demo table");
+  }
+
+  private Table getMockTable(String name, String comment) {
+    Table mockTable = mock(Table.class);
+    org.apache.gravitino.rel.Column mockColumnInt =
+        getMockColumn("id", Types.IntegerType.get(), "This is a int column", false, true);
+    org.apache.gravitino.rel.Column mockColumnString =
+        getMockColumn("name", Types.StringType.get(), "This is a string column", true, false);
+
+    when(mockTable.name()).thenReturn(name);
+    when(mockTable.comment()).thenReturn(comment);
+    when(mockTable.columns())
+        .thenReturn(new org.apache.gravitino.rel.Column[] {mockColumnInt, mockColumnString});
+
+    return mockTable;
+  }
+
+  private org.apache.gravitino.rel.Column getMockColumn(
+      String name, Type dataType, String comment, boolean nullable, boolean autoIncrement) {
+
+    org.apache.gravitino.rel.Column mockColumn = mock(org.apache.gravitino.rel.Column.class);
+    when(mockColumn.name()).thenReturn(name);
+    when(mockColumn.dataType()).thenReturn(dataType);
+    when(mockColumn.comment()).thenReturn(comment);
+    when(mockColumn.nullable()).thenReturn(nullable);
+    when(mockColumn.autoIncrement()).thenReturn(autoIncrement);
 
-    return mockAudit;
+    return mockColumn;
   }
 }