Add limits overriding with system properties

lib/src/main/java/de/siegmar/fastcsv/util/Limits.java

@@ -2,6 +2,16 @@
 
 /**
  * The {@code Limits} class defines the maximum limits for various fields and records in a CSV file.
+ * <p>
+ * Example use:
+ * <pre>{@code
+ * System.setProperty("fastcsv.max.field.size", "1024");
+ * }</pre>
+ * <p>
+ * Or using VM options:
+ * <pre>{@code
+ * -Dfastcsv.max.field.count=1024
+ * }</pre>
  */
 public final class Limits {
 
@@ -10,13 +20,13 @@ public final class Limits {
      * The value is set to 16,777,216 characters (16 to 64 MiB depending on the circumstance of multibyte character
      * utilization).
      */
-    public static final int MAX_FIELD_SIZE = 16 * 1024 * 1024;
+    public static final int MAX_FIELD_SIZE = getIntProperty("fastcsv.max.field.size", 16 * 1024 * 1024);
 
     /**
      * The {@code MAX_FIELDS_SIZE} constant defines the maximum number of fields per record.
      * The value is set to 16,384.
      */
-    public static final int MAX_FIELD_COUNT = 16 * 1024;
+    public static final int MAX_FIELD_COUNT = getIntProperty("fastcsv.max.field.count", 16 * 1024);
 
     /**
      * The {@code MAX_RECORD_SIZE} constant defines the maximum size for all fields combined in a CSV record.
@@ -27,4 +37,26 @@ public final class Limits {
     private Limits() {
     }
 
+    /**
+     * Retrieves the system property value if presented, otherwise default value is returned.
+     * If the property cannot be parsed as an integer, an {@code IllegalArgumentException} is thrown.
+     *
+     * @param key The system property key.
+     * @param defaultValue The default value to use if the system property is not set or is invalid.
+     * @return The system property value as an integer or the default value if the property is not set or is invalid.
+     * @throws IllegalArgumentException If the system property value cannot be parsed as an integer.
+     */
+    static int getIntProperty(final String key, final int defaultValue) {
+        final String value = System.getProperty(key);
+
+        if (value == null) {
+            return defaultValue;
+        }
+
+        try {
+            return Integer.parseInt(value);
+        } catch (final NumberFormatException e) {
+            throw new IllegalArgumentException("Invalid format for system property " + key, e);
+        }
+    }
 }

lib/src/test/java/de/siegmar/fastcsv/util/LimitsTest.java

@@ -0,0 +1,67 @@
+package de.siegmar.fastcsv.util;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class LimitsTest {
+
+    @BeforeEach
+    void setup() {
+        System.clearProperty("fastcsv.max.field.size");
+        System.clearProperty("fastcsv.max.field.count");
+    }
+
+    @AfterEach
+    void cleanup() {
+        System.clearProperty("fastcsv.max.field.size");
+        System.clearProperty("fastcsv.max.field.count");
+    }
+
+    @Test
+    void defaultMaxFieldSize() {
+        assertEquals(16 * 1024 * 1024, Limits.MAX_FIELD_SIZE, "Default max field size should be correct");
+    }
+
+    @Test
+    void customMaxFieldSize() {
+        System.setProperty("fastcsv.max.field.size", "100000");
+
+        assertEquals(100000, Limits.getIntProperty("fastcsv.max.field.size", 16 * 1024 * 1024),
+                "Custom max field size should be respected");
+    }
+
+    @Test
+    void defaultMaxFieldCount() {
+        assertEquals(16 * 1024, Limits.MAX_FIELD_COUNT, "Default max field count should be correct");
+    }
+
+    @Test
+    void customMaxFieldCount() {
+        System.setProperty("fastcsv.max.field.count", "200");
+
+        assertEquals(200, Limits.getIntProperty("fastcsv.max.field.count", 16 * 1024),
+                "Custom max field count should be respected");
+    }
+
+    @Test
+    void invalidMaxFieldSizeThrowsException() {
+        System.setProperty("fastcsv.max.field.size", "invalid");
+
+        assertThrows(IllegalArgumentException.class,
+                () -> Limits.getIntProperty("fastcsv.max.field.size", 16 * 1024 * 1024),
+                "Should throw IllegalArgumentException for invalid integer format");
+    }
+
+    @Test
+    void testMaxRecordSizeBasedOnMaxFieldSize() {
+        System.setProperty("fastcsv.max.field.size", "4000000");
+
+        assertEquals(4 * 4000000,
+                4 * Limits.getIntProperty("fastcsv.max.field.size", 16 * 1024 * 1024),
+                "MAX_RECORD_SIZE should be four times MAX_FIELD_SIZE");
+    }
+}