fixed DataTypeConverter for nested arrays when target accumulator was set to null

chernser · chernser · commit 76943676e5cc · 2026-01-27T10:32:21.000-08:00
diff --git a/client-v2/src/main/java/com/clickhouse/client/api/internal/DataTypeConverter.java b/client-v2/src/main/java/com/clickhouse/client/api/internal/DataTypeConverter.java
@@ -261,12 +261,16 @@ protected void onItem(Object item, ListConversionState<Object> state) {
         }
 
         public String convertAndReset(Object list, Appendable acc, ClickHouseColumn column) {
+            // Save current state to handle re-entrancy (nested array conversion)
+            ClickHouseColumn prevColumn = this.column;
+            Appendable prevAppendable = this.appendable;
             try {
                 setColumn(column);
                 return super.convert(list, acc);
             } finally {
-                this.column = null;
-                setAccumulator(null);
+                // Restore previous state for re-entrant calls
+                this.column = prevColumn;
+                setAccumulator(prevAppendable);
             }
         }
     }
@@ -292,12 +296,16 @@ protected void onItem(Object item, ListConversionState<List<?>> state) {
         }
 
         public String convertAndReset(List<?> list, Appendable acc, ClickHouseColumn column) {
+            // Save current state to handle re-entrancy (nested array conversion)
+            ClickHouseColumn prevColumn = this.column;
+            Appendable prevAppendable = this.appendable;
             try {
                 setColumn(column);
                 return super.convert(list, acc);
             } finally {
-                this.column = null;
-                setAccumulator(null);
+                // Restore previous state for re-entrant calls
+                this.column = prevColumn;
+                setAccumulator(prevAppendable);
             }
         }
     }
diff --git a/jdbc-v2/src/test/java/com/clickhouse/jdbc/DataTypeTests.java b/jdbc-v2/src/test/java/com/clickhouse/jdbc/DataTypeTests.java
@@ -1067,6 +1067,65 @@ public void testNestedArrays() throws Exception {
         }
     }
 
+    /**
+     * Test for https://github.com/ClickHouse/clickhouse-java/issues/2723
+     * getString() on nested arrays was failing with NullPointerException due to re-entrancy bug
+     * in DataTypeConverter when converting nested arrays to string representation.
+     */
+    @Test(groups = { "integration" })
+    public void testNestedArrayToString() throws SQLException {
+        // Test 1: Simple nested array - getString on Array(Array(Int32))
+        try (Connection conn = getJdbcConnection()) {
+            try (Statement stmt = conn.createStatement()) {
+                try (ResultSet rs = stmt.executeQuery("SELECT [[1, 2, 3], [4, 5, 6]] as nested_array")) {
+                    assertTrue(rs.next());
+                    // This was throwing NullPointerException before the fix
+                    String result = rs.getString("nested_array");
+                    assertEquals(result, "[[1, 2, 3], [4, 5, 6]]");
+                }
+            }
+        }
+
+        // Test 2: Query similar to issue #2723 with splitByChar returning array
+        // The original issue was that getString() on an array column inside a CASE/WHEN
+        // would cause NPE. This test verifies that getString() works correctly on arrays.
+        try (Connection conn = getJdbcConnection()) {
+            try (Statement stmt = conn.createStatement()) {
+                String query = "SELECT " +
+                        "splitByChar('_', 'field1_field2_field3') as split_result, " +
+                        "CASE " +
+                        "    WHEN " +
+                        "         splitByChar('_', 'field1_field2_field3')[1] IN ('field1', 'field2') " +
+                        "         AND match( " +
+                        "             splitByChar('_', 'field1_field2_field3')[2], " +
+                        "             '(field1|field2|field3)' " +
+                        "         ) " +
+                        "        THEN 'Matched' " +
+                        "    ELSE 'NotMatched' " +
+                        "END AS action_to_do";
+                try (ResultSet rs = stmt.executeQuery(query)) {
+                    assertTrue(rs.next());
+                    // The key test is that getString() doesn't throw NPE on array column
+                    String splitResult = rs.getString("split_result");
+                    assertEquals(splitResult, "['field1', 'field2', 'field3']");
+                    String actionResult = rs.getString("action_to_do");
+                    assertEquals(actionResult, "Matched");
+                }
+            }
+        }
+
+        // Test 3: Deeply nested arrays - Array(Array(Array(String)))
+        try (Connection conn = getJdbcConnection()) {
+            try (Statement stmt = conn.createStatement()) {
+                try (ResultSet rs = stmt.executeQuery("SELECT [[['a', 'b'], ['c']], [['d', 'e', 'f']]] as deep_nested")) {
+                    assertTrue(rs.next());
+                    String result = rs.getString("deep_nested");
+                    assertEquals(result, "[[['a', 'b'], ['c']], [['d', 'e', 'f']]]");
+                }
+            }
+        }
+    }
+
     @Test(groups = { "integration" })
     public void testMapTypes() throws SQLException {
         runQuery("CREATE TABLE test_maps (order Int8, "

Original file line number	Diff line number	Diff line change
`@@ -261,12 +261,16 @@ protected void onItem(Object item, ListConversionState<Object> state) {`
`261`	`261`	`}`
`262`	`262`
`263`	`263`	`public String convertAndReset(Object list, Appendable acc, ClickHouseColumn column) {`
	`264`	`+ // Save current state to handle re-entrancy (nested array conversion)`
	`265`	`+ ClickHouseColumn prevColumn = this.column;`
	`266`	`+ Appendable prevAppendable = this.appendable;`
`264`	`267`	`try {`
`265`	`268`	`setColumn(column);`
`266`	`269`	`return super.convert(list, acc);`
`267`	`270`	`} finally {`
`268`		`- this.column = null;`
`269`		`- setAccumulator(null);`
	`271`	`+ // Restore previous state for re-entrant calls`
	`272`	`+ this.column = prevColumn;`
	`273`	`+ setAccumulator(prevAppendable);`
`270`	`274`	`}`
`271`	`275`	`}`
`272`	`276`	`}`
`@@ -292,12 +296,16 @@ protected void onItem(Object item, ListConversionState<List<?>> state) {`
`292`	`296`	`}`
`293`	`297`
`294`	`298`	`public String convertAndReset(List<?> list, Appendable acc, ClickHouseColumn column) {`
	`299`	`+ // Save current state to handle re-entrancy (nested array conversion)`
	`300`	`+ ClickHouseColumn prevColumn = this.column;`
	`301`	`+ Appendable prevAppendable = this.appendable;`
`295`	`302`	`try {`
`296`	`303`	`setColumn(column);`
`297`	`304`	`return super.convert(list, acc);`
`298`	`305`	`} finally {`
`299`		`- this.column = null;`
`300`		`- setAccumulator(null);`
	`306`	`+ // Restore previous state for re-entrant calls`
	`307`	`+ this.column = prevColumn;`
	`308`	`+ setAccumulator(prevAppendable);`
`301`	`309`	`}`
`302`	`310`	`}`
`303`	`311`	`}`