Question

我正在使用Java将查询从数据库写入CSV文件。我该怎么做才能循环查询结果，以便在CSV文件中逐行显示。以下是我的代码片段。

StringBuilder sb =  new StringBuilder();

sb.append(reportBO.projectList(this.getSearchBean());
sb,append(',');
sb.append('\n');

假设我的查询是

SELECT * FROM PROJECT

以下是我的预期结果。

Answer 1

如下所述循环结果集并将其写入文件

    while (rs.next()){
         sb.append(rs.getString(<ColumnName1>));
         sb.append(',');
         sb.append(rs.getString(<ColumnName2>));
         sb.append(',');
         sb.append(rs.getString(<ColumnName3>));
         sb.append('\n');
    }

如果要将数据填充到StringBuffer中，请确保以固定间隔（例如，每1000行）将其写入文件。否则，如果结果包含大量行，则可能会获得OutOfMemoryException。

Answer 2

您需要CSV编写器才能正确处理此问题。值可以包含逗号，引号，换行符，并且必须正确转义。

从您的代码中，您似乎正在尝试编写bean而不是直接从ResultSet中获取内容。在这种情况下，您可以尝试univocity-parsers：

//creates a configuration object that allows you to determine how to 
//format your CSV output, among many other things. Check the tutorial.
CsvWriterSettings settings = new CsvWriterSettings();

//Configures the parser to process input objects using the BeanWriterProcessor. 
//This reads the data from your java beans. In this case the type is "TestBean"
//but in yours it seems that would be something like "SearchBean".
settings.setRowWriterProcessor(new BeanWriterProcessor<TestBean>(TestBean.class));

//Defines the headers to print out to the output. My "TestBean" class has the 
//following fields. Adjust this to reflect the fields in your "SearchBean"
settings.setHeaders("amount", "pending", "date", "quantity", "comments");

// Creates a CsvWriter with the settings above
CsvWriter writer = new CsvWriter(new FileWriter(new File("/path/to/file.csv")), settings);

//Loads the beans from the database. 
//The "loadBeanList" method is something you should implement. 
List<TestBean> beansToPersist = loadBeanList();

//With a list of beans loaded from the database, you can simply call this 
//and write everything into your CSV file. You can also write beans one by one.
writer.processRecordsAndClose(beansToPersist);

披露：我是这个图书馆的作者。它是开源和免费的（Apache V2.0许可证）。

Answer 3

以下是我解决方案的方法。希望它可以帮助某人。谢谢大家的帮助......

for (int i = 0; i < ((List<BaseDTOInf>) getProjectList(searchBean)).size();i++) {

                BaseDTO list = (BaseDTO) getProjectList(searchBean).get(i);
                list.getDataMap().get("A");
                list.getDataMap().get("B");
                list.getDataMap().get("C");
                list.getDataMap().get("D");
                list.getDataMap().get("E");
                list.getDataMap().get("F");

                sb.append(list.getDataMap().get("A"));
                sb.append(',');
                sb.append(list.getDataMap().get("B"));
                sb.append(',');
                sb.append(list.getDataMap().get("C"));
                sb.append(',');
                sb.append(list.getDataMap().get("D"));
                sb.append(',');
                sb.append(list.getDataMap().get("E"));
                sb.append(',');
                sb.append('\n');

            }

从数据库循环查询

3 个答案: