File API

@Test
public void readFileLinesToJson() {
    FileUtils.readFileLinesToJson("/mappings/doctorinfo_mapping.json");
}

/**
 * 读取resource文件下的mapping
 * @param filePath
 * @return
 */
public static StringBuffer readFileLinesToJson(String filePath) {

    StringBuffer stringBuffer = new StringBuffer();
    try {
        ClassPathResource classPathResource = new ClassPathResource(filePath);
        InputStream inputStream = classPathResource.getInputStream();

        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));

        String temp;
        while (null != (temp = bufferedReader.readLine())) {
            stringBuffer.append(temp);
        }
        bufferedReader.close();
        inputStream.close();
    } catch (Exception e) {
        log.debug(e.getMessage());
    }
    return stringBuffer;
}

Java 8逐行读取文件:在此示例中，我将按行读取文件内容并在控制台打印输出。

Path filePath = Paths.get("c:/temp", "data.txt");
//try-with-resources语法,不用手动的编码关闭流
try (Stream<String> lines = Files.lines( filePath )) 
{
    lines.forEach(System.out::println);
} 
catch (IOException e) 
{
    e.printStackTrace();//只是测试用例，生产环境下不要这样做异常处理
}

Java8读取文件,过滤行:我们将文件内容读取为Stream。然后，我们将过滤其中包含单词"password"的所有行。

Path filePath = Paths.get("c:/temp", "data.txt");
try (Stream<String> lines = Files.lines(filePath)){
 
     List<String> filteredLines = lines
                    .filter(s -> s.contains("password"))
                    .collect(Collectors.toList());
      
     filteredLines.forEach(System.out::println);
 
} catch (IOException e) {
    e.printStackTrace();//只是测试用例，生产环境下不要这样做异常处理
}

Java7使用FileReader读取文件:

public static void main(String[] args) {

    // 启动第一个线程
    new Thread(() -> {
        doSomeThing("/Users/Documents/projects/logs/articleId.txt");
    }).start();
 }   
  
private static void doSomeThing(String filenamePath) {
    try {
        FileReader fr = new FileReader(filenamePath);
        BufferedReader bf = new BufferedReader(fr);
        String str;
        while ((str = bf.readLine()) != null) {
            log.info("文章:{}", str);
        }
        bf.close();
        fr.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return;
}

Java7读取CSV文件：

public class ReadFileCsvUtils {

    private static final String fileNamePath = "/Users/Downloads/Data/faculty.csv";

    public static void main(String[] args) {
        readCsvFile(fileNamePath);
    }

    public static void readCsvFile(String fileNamePath) {
        try {
            // 换成你的文件名
            BufferedReader reader = new BufferedReader(new FileReader(fileNamePath));
            reader.readLine();//第一行信息，为标题信息，不用,如果需要，注释掉
            String line = null;
            while ((line = reader.readLine()) != null) {
                // CSV格式文件为逗号分隔符文件，这里根据逗号切分
                String[] item = line.split(",");
                System.out.println(new Gson().toJson(item));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Java7写TXT文件：

// FileWriter的第二个参数代表是否追加
BufferedWriter writer = new BufferedWriter(new FileWriter(targetFile, true));
// 字符串中使用换行：\r\n
writer.write(ss);
writer.newLine();
writer.close();

Java7写CSV文件：

public void writeCsvFile(String fileNamePath) {

    List<String> data = new ArrayList();
    try {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(fileNamePath, true));
        bufferedWriter.write("第一列, 第二列, 第三列, 第四列");
        for (int i = 0; i < data.size(); i++) {

            bufferedWriter.write(data.get(i));
            bufferedWriter.newLine();
        }
        bufferedWriter.flush();
        bufferedWriter.close();

    } catch (Exception e) {
        log.error("error:" + e.getMessage());
    }
}

public class CutFileUtils {

    /**
     * 按指定大小切割文件
     * @param args
     */
    public static void main(String[] args) {
        //调用cutFile()函数 传人参数分别为 （原大文件，切割后存放的小文件的路径，切割规定的内存大小）
        cutFile("/Users/Documents/projects/logs/searchmanager/Data/logs/service/SearchManager.2020-11-18-1.log",
                "/Users/Documents/projects/logs/searchmanager/", 1024 * 1024 * 1000);
    }


    /**
     * @param src    需要切割的文件
     * @param endsrc 切割后文件的存放路径
     * @param num    每个文件的大小
     */
    public static void cutFile(String src, String endsrc, int num) {
        FileInputStream fis = null;
        File file = null;
        try {
            fis = new FileInputStream(src);
            file = new File(src);
            //创建规定大小的byte数组
            byte[] b = new byte[num];
            int len = 0;
            //name为以后的小文件命名做准备
            int name = 1;
            //遍历将大文件读入byte数组中，当byte数组读满后写入对应的小文件中
            while ((len = fis.read(b)) != -1) {
                //分别找到原大文件的文件名和文件类型，为下面的小文件命名做准备
                String name2 = file.getName();
                int lastIndexOf = name2.lastIndexOf(".");
                String substring = name2.substring(0, lastIndexOf);
                String substring2 = name2.substring(lastIndexOf, name2.length());
                FileOutputStream fos = new FileOutputStream(endsrc + "/" + substring + "-" + name + substring2);
                //将byte数组写入对应的小文件中
                fos.write(b, 0, len);
                //结束资源 fos.close();
                name++;
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fis != null) {
                    //结束资源
                    fis.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}