Java - 将哈希图写入 csv 文件 [英] Java - Write hashmap to a csv file

问题描述

我有一个带有字符串键和字符串值的哈希图.它包含大量的键和它们各自的值.

I have a hashmap with a String key and String value. It contains a large number of keys and their respective values.

例如:

key | value
abc | aabbcc
def | ddeeff

我想将此哈希图写入 csv 文件，以便我的 csv 文件包含如下行:

I would like to write this hashmap to a csv file such that my csv file contains rows as below:

abc,aabbcc
def,ddeeff

我在这里使用 supercsv 库尝试了以下示例:http://javafascination.blogspot.com/2009/07/csv-write-using-java.html.但是，在此示例中，您必须为要添加到 csv 文件的每一行创建一个 hashmap.我有大量的键值对，这意味着需要创建几个哈希图，每个哈希图都包含一行的数据.我想知道是否有更优化的方法可用于此用例.

I tried the following example here using the supercsv library: http://javafascination.blogspot.com/2009/07/csv-write-using-java.html. However, in this example, you have to create a hashmap for each row that you want to add to your csv file. I have a large number of key value pairs which means that several hashmaps, with each containing data for one row need to be created. I would like to know if there is a more optimized approach that can be used for this use case.

推荐答案

当您的问题是如何使用 Super CSV 执行此操作时，我想我会加入(作为项目的维护者).

As your question is asking how to do this using Super CSV, I thought I'd chime in (as a maintainer of the project).

我最初以为您可以使用 CsvBeanWriter 和 "key", "value" 的名称映射数组来迭代映射的条目集，但这并没有工作，因为 HashMap 的内部实现不允许反射来获取键/值.

I initially thought you could just iterate over the map's entry set using CsvBeanWriter and a name mapping array of "key", "value", but this doesn't work because HashMap's internal implementation doesn't allow reflection to get the key/value.

所以你唯一的选择是使用 CsvListWriter 如下.至少这样您就不必担心转义 CSV(这里的每个其他示例都只是用逗号连接...aaarrggh！):

So your only option is to use CsvListWriter as follows. At least this way you don't have to worry about escaping CSV (every other example here just joins with commas...aaarrggh!):

@Test
public void writeHashMapToCsv() throws Exception {
    Map<String, String> map = new HashMap<>();
    map.put("abc", "aabbcc");
    map.put("def", "ddeeff");

    StringWriter output = new StringWriter();
    try (ICsvListWriter listWriter = new CsvListWriter(output, 
         CsvPreference.STANDARD_PREFERENCE)){
        for (Map.Entry<String, String> entry : map.entrySet()){
            listWriter.write(entry.getKey(), entry.getValue());
        }
    }

    System.out.println(output);
}

输出:

abc,aabbcc
def,ddeeff

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