将结果集中的值写入文本文件（.txt 文件）答案

【问题标题】：To write the value from resultset to text file (.txt file)将结果集中的值写入文本文件（.txt 文件）
【发布时间】：2015-09-20 20:22:58
【问题描述】：

请帮助我处理下面的代码，因为我想将结果集中的值写入 txt 文件

代码

while (rs.next()){
    FileWriter fstream = new FileWriter(file);
    BufferedWriter out = new BufferedWriter(fstream);

    out.write(Integer.toString(rs.getInt("SBL_PRODUCT_ID")) + ", ");
    out.write(Integer.toString(rs.getInt("SBL_TARIFF_ID")) + ", ");
    out.write(rs.getString("PRODUCT_DESCRIPTION") + ", ");
    out.write(rs.getString("SERVICE_TYPE") + ", ");
    out.write(Integer.toString(rs.getInt("MARKET_CLASS")) + ", ");
    out.write(rs.getString("ENTITY_TYPE") + ", ");
    out.newLine();
    /*out.write(System.getProperty("line.separator"));*/

    System.out.println("Completed writing into text file");
    out.close();
}

txt 文件中的必需输出

4087, 98, POSTE SIM, Deal [SoHo Flat Tariff Recurring Charge, Prepaid], /service/telco/SIM, 101, DEAL

4087, 99, POSTE SIM, Deal [SoHo Flat Tariff Recurring Charge, Prepaid], /service/telco/SIM, 101, DEAL

4087, 100, POSTE SIM, Deal [SoHo Flat Tariff Recurring Charge, Prepaid], /service/telco/SIM, 101, DEAL

4087, 101, POSTE SIM, Deal [SoHo Flat Tariff Recurring Charge, Prepaid], /service/telco/SIM, 101, DEAL

我得到的当前输出只是结果集中的最后一个值，即下面的一行

电流输出

4087, 101, POSTE SIM, Deal [SoHo Flat Tariff Recurring Charge, Prepaid], /service/telco/SIM, 101, DEAL

请帮我解决这个问题:(

【问题讨论】：

写完所有内容后打开文件，然后关闭一次
我没听懂你能不能请你提供一个sn-p
您正在打开文件，写入和关闭ResultSet 的每次迭代（对于ResultSet 中的每一行），您不仅没有附加到文件，这是一个很多不必要的开销
Writing a large ResultSet to a File的可能重复

标签： java text-files multiple-resultsets

【解决方案1】：

来自 GitHub：https://github.com/OhadR/ohadr.common/blob/master/src/main/java/com/ohadr/common/utils/resultset/ResultSetConverters.java

public static void writeResultSetToWriter(ResultSet resultSet, PrintWriter writer) throws SQLException
{
ResultSetMetaData metadata = resultSet.getMetaData();
int numColumns = metadata.getColumnCount();
int numRows = 0;

while(resultSet.next())             //iterate rows
{
    ++numRows;
    JSONObject obj = new JSONObject();      //extends HashMap
    for (int i = 1; i <= numColumns; ++i)           //iterate columns
    {
        String column_name = metadata.getColumnName(i);
        obj.put(column_name, resultSet.getObject(column_name));
    }
    writer.println(obj.toJSONString());

    if(numRows % 1000 == 0)
        writer.flush();
}

}

【讨论】：

【解决方案2】：

每次创建文件写入器时，都会覆盖文件。将其更改为：

FileWriter fstream = new FileWriter(file);
BufferedWriter out = new BufferedWriter(fstream);
while (rs.next()) {            
        out.write(Integer.toString(rs.getInt("SBL_PRODUCT_ID")) + ", ");
        out.write(Integer.toString(rs.getInt("SBL_TARIFF_ID")) + ", ");
        out.write(rs.getString("PRODUCT_DESCRIPTION") + ", ");
        out.write(rs.getString("SERVICE_TYPE") + ", ");
        out.write(Integer.toString(rs.getInt("MARKET_CLASS")) + ", ");
        out.write(rs.getString("ENTITY_TYPE") + ", ");
        out.newLine();
        /*out.write(System.getProperty("line.separator"));*/
}
System.out.println("Completed writing into text file");
out.close();

或者，您可以在 FileWriter 中设置 append 标志：

FileWriter fstream = new FileWriter(file, true);

虽然这不如只打开一次文件那么有效。

【讨论】：

没错。正要提出同样的建议。另一种更好的编码方式是@MadProgrammer 建议的使用Java 7 特性try-with-resources

【解决方案3】：

打开文件一次，将内容写入其中，然后在所有内容写入后关闭，例如

try (BufferedWriter out = new BufferedWriter(new FileWriter(file))) {
    while (rs.next()) {
        out.write(Integer.toString(rs.getInt("SBL_PRODUCT_ID")) + ", ");
        out.write(Integer.toString(rs.getInt("SBL_TARIFF_ID")) + ", ");
        out.write(rs.getString("PRODUCT_DESCRIPTION") + ", ");
        out.write(rs.getString("SERVICE_TYPE") + ", ");
        out.write(Integer.toString(rs.getInt("MARKET_CLASS")) + ", ");
        out.write(rs.getString("ENTITY_TYPE") + ", ");
        out.newLine();
    }
    System.out.println("Completed writing into text file");
}

查看The try-with-resources Statement了解更多详情

【讨论】：

非常感谢 :) :)
很高兴能帮上忙 ;)