按指定格式写入CSV异常：最后一行缺失竖线问题排查

我来帮你排查并解决这个竖线分隔CSV的格式异常问题，咱们一步步梳理：

需求目标 #

我们需要生成符合以下格式的竖线分隔CSV：

Redemption Reference Code|Status|Delivery company|Shipper Tracking Number|Comments
2006995040|Shipped|USPS|ABCD12345|Order SHIPPED
2006995042|Cancelled|||INVALID Address
2006995048|Ordered|USPS|ABCD12345|Order SHIPPED

当前实现代码 #

1. 订单数据收集逻辑 #

private void accumulateOrdersFromPlacement(){
    int count = 0;
    for (int i = 0; i < orderIds.size(); i++) {
        if (count == 0) {
            outPutLineData.add(orderIds.get(i));
            outPutLineData.add("Cancelled");
            outPutLineData.add("");
            outPutLineData.add(" ");
            outPutLineData.add(" ");
            cancelledStatusLineItems.add(orderIds.get(i));
            count++;
        } else if (count == 1) {
            outPutLineData.add(orderIds.get(i));
            outPutLineData.add("Shipped");
            if (outPutLineData.contains("Shipped")) {
                outPutLineData.add("USPS");
                outPutLineData.add("order SHIPPED");
                outPutLineData.add("");
            }
            shippedStatusLineItems.add(orderIds.get(i));
            count++;
        } else if (count == 2) {
            outPutLineData.add(orderIds.get(i));
            outPutLineData.add("No Longer Available");
            outPutLineData.add("");
            outPutLineData.add(" ");
            outPutLineData.add(" ");
            count++;
            nlaStatusLineItems.add(orderIds.get(i));
        } else if (count == 3) {
            outPutLineData.add(orderIds.get(i));
            outPutLineData.add("Ordered");
            outPutLineData.add("");
            outPutLineData.add(" ");
            outPutLineData.add(" ");
            orderedStatusLineItems.add(orderIds.get(i));
            count = 0;
        }
    }
}

2. 文件生成逻辑 #

private File createFile(final File directory) {
    FileWriter fw = null;
    File tempFile = null;
    try {
        directory.mkdir();
        tempFile = new File(".//FidelityFulfillment//" + generateFileName(countyThreeLetterCode, "FidelityFulfillment", ".csv", date));
        logReport(GenericConstants.NEW_LINE + "Fulfillment file creating:", tempFile.getName());
        fw = new FileWriter(tempFile, true);
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile, true))) {
            writer.write(generateHeaderLine());
            writer.newLine();
            for (int y = 1; y < outPutLineData.size(); y++) {
                if (y % 5 < 4) {
                    writer.write(outPutLineData.get(y-1) + fieldSeperator);
                    logReport(outPutLineData.get(y - 1) + fieldSeperator);
                } else {
                    writer.write(outPutLineData.get(y-1));
                    logReport(outPutLineData.get(y));
                }
                if (y % 5 == 0) {
                    writer.newLine();
                    logReport("newline");
                }
            }
            writer.close();
        } catch (final IOException e) {
            e.printStackTrace();
            final String err = "Unable to write file due to : " + e;
            logReport(GenericConstants.NEW_LINE + "Unable to create temp local File");
        } finally {
            fw.close();
        }
    }catch (Exception e){
        e.printStackTrace();
    }
    return tempFile;
}

问题现象 #

实际输出的CSV存在格式异常，最后一行缺失竖线，字段不完整：

Redemption Reference Code|Status|Delivery company|ShipperTrackingNumber|Comments
2006964032|Cancelled|| | 
newline
2006964034|Shipped|USPS|| 
newline
2006964036|No Longer Available|| 

问题排查与修复 #

1. 核心问题分析 #

文件生成的循环逻辑存在两个致命问题：

• 遗漏最后一个元素：循环条件y < outPutLineData.size()导致最后一个元素（索引size-1）永远不会被写入，直接造成最后一行字段缺失
• 字段分隔逻辑混乱：用y%5 <4判断是否加分隔符的逻辑，在处理非5的整数倍元素时，会导致最后一行的分隔符不完整

另外还有一个次要问题：代码中创建了重复的FileWriter，既容易导致资源泄露，也可能造成文件追加异常。

2. 修复方案 #

方案一：重构文件生成的循环逻辑

把循环改成按字段遍历，确保每个元素都被处理，并且每行的5个字段严格用竖线分隔：

// 替换原有的循环代码
for (int i = 0; i < outPutLineData.size(); i++) {
    String field = outPutLineData.get(i);
    // 不是当前行最后一个字段，就添加分隔符
    if ((i + 1) % 5 != 0) {
        writer.write(field + fieldSeperator);
        logReport(field + fieldSeperator);
    } else {
        // 当前行最后一个字段，直接写入后换行
        writer.write(field);
        logReport(field);
        writer.newLine();
        logReport("newline");
    }
}

方案二：清理冗余代码与优化

• 去掉重复的FileWriter fw，用try-with-resources自动管理资源
• 用directory.mkdirs()代替mkdir()，确保父目录不存在时也能创建成功
• 移除accumulateOrdersFromPlacement中多余的if (outPutLineData.contains("Shipped"))判断（刚添加的元素必然存在，逻辑冗余）

修复后的完整createFile方法：

private File createFile(final File directory) {
    File tempFile = null;
    try {
        // 确保所有父目录都能被创建
        directory.mkdirs();
        tempFile = new File(".//FidelityFulfillment//" + generateFileName(countyThreeLetterCode, "FidelityFulfillment", ".csv", date));
        logReport(GenericConstants.NEW_LINE + "Fulfillment file creating:", tempFile.getName());
        
        // try-with-resources自动关闭writer，无需手动调用close
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile))) {
            writer.write(generateHeaderLine());
            writer.newLine();
            
            // 遍历所有字段，按每行5个字段处理
            for (int i = 0; i < outPutLineData.size(); i++) {
                String field = outPutLineData.get(i);
                if ((i + 1) % 5 != 0) {
                    writer.write(field + fieldSeperator);
                    logReport(field + fieldSeperator);
                } else {
                    writer.write(field);
                    logReport(field);
                    writer.newLine();
                    logReport("newline");
                }
            }
        } catch (final IOException e) {
            e.printStackTrace();
            String err = "Unable to write file due to : " + e;
            logReport(GenericConstants.NEW_LINE + err);
        }
    } catch (Exception e) {
        e.printStackTrace();
        logReport(GenericConstants.NEW_LINE + "Failed to create file: " + e.getMessage());
    }
    return tempFile;
}

3. 验证效果 #

修复后，生成的CSV每行都会严格包含5个字段，用4个竖线分隔，不会出现最后一行缺失竖线或字段的情况，完全符合需求格式。

内容的提问来源于stack exchange，提问作者Soorya Thomas