fix csv write ArrayIndexOutOfBoundsException error, for issue #2848

core/src/main/java/com/alibaba/fastjson2/support/csv/CSVWriterUTF16.java

@@ -216,6 +216,12 @@ public void writeDecimal(BigDecimal value) {
 
         String str = value.toString();
         int strlen = str.length();
+
+        int minCapacity = off + 24;
+        if (minCapacity - this.chars.length > 0) {
+            flush();
+        }
+
         str.getChars(0, strlen, chars, off);
         off += strlen;
     }

core/src/main/java/com/alibaba/fastjson2/support/csv/CSVWriterUTF8.java

@@ -219,6 +219,12 @@ public void writeDecimal(BigDecimal value) {
 
         String str = value.toString();
         int strlen = str.length();
+
+        int minCapacity = off + 24;
+        if (minCapacity - this.bytes.length > 0) {
+            flush();
+        }
+
         str.getBytes(0, strlen, bytes, off);
         off += strlen;
     }

core/src/test/java/com/alibaba/fastjson2/issues_2800/Issue2848.java

@@ -0,0 +1,34 @@
+package com.alibaba.fastjson2.issues_2800;
+
+import com.alibaba.fastjson2.support.csv.CSVWriter;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.math.BigDecimal;
+import java.nio.charset.StandardCharsets;
+
+public class Issue2848 {
+    @Test
+    public void test() throws Exception {
+        StringBuilder buf = new StringBuilder();
+        for (int i = 0; i < 65531; i++) {
+            buf.append('1');
+        }
+
+        String str = buf.toString();
+
+        try (CSVWriter writer = CSVWriter.of()) {
+            writer.writeValue(str);
+            writer.writeComma();
+            writer.writeValue(new BigDecimal("1.00"));
+            writer.writeComma();
+        }
+
+        try (CSVWriter writer = CSVWriter.of(new ByteArrayOutputStream(), StandardCharsets.UTF_16)) {
+            writer.writeValue(str);
+            writer.writeComma();
+            writer.writeValue(new BigDecimal("1.00"));
+            writer.writeComma();
+        }
+    }
+}