java 代码碎片

一、java 按行将一篇文本读入到 List 中（保留换行）

public static List<String> splitTextToLineList(String text) {
    List<String> lines = new ArrayList<>();
    String[] splits = text.split("\n");
    for (int i = 0; i < splits.length; i++) {
        if (i != splits.length - 1) {
            lines.add(splits[i] + "\n");
        } else if (i == splits.length - 1) {
            if (text.endsWith("\n")) {
                lines.add(splits[i] + "\n");
            } else {
                lines.add(splits[i]);
            }
        }
    }
    return lines;
}

二、以追加的方式写文件

public static void writeStrToFile(String fileName, String str) {
    try {
        BufferedWriter out = new BufferedWriter(new FileWriter(fileName, true));
        out.write(str);
        out.close();
    } catch (IOException e) {
        System.out.println("exception occoured" + e);
    }
}

三、反射的用法

package com.bluesky.bubble.paragraph.util;

public class ParagraphSpliterUtil {
    private static boolean isFragmentaryOrdinalBlock(int begin, int end, String text) {
        // TODO
        return fragmentaryOrdinalBlock;
    }
}

// ================================
@Test
public void testIsFragmentaryOrdinalBlock() throws Exception {
    String text = "He is a good man, and he has a dog.";
    Class<?> clazz = Class.forName("com.bluesky.bubble.paragraph.util.ParagraphSpliterUtil");
    Constructor<ParagraphSpliterUtil> constructor = (Constructor<ParagraphSpliterUtil>) clazz.getConstructor();
    ParagraphSpliterUtil spliterUtil = constructor.newInstance();
    Method method = clazz.getDeclaredMethod("isFragmentaryOrdinalBlock", int.class, int.class, String.class);
    method.setAccessible(true);
    Boolean result = (Boolean) method.invoke(spliterUtil, 0, text.length(), text);
    assertTrue(result);
}

四、对象实现 Comparable 接口

public class Span implements Comparable<Span>{

    private int begin;
    private int end;

    public Span(int begin, int end) {
        this.begin = begin;
        this.end = end;
    }

    public int getBegin() {
        return begin;
    }

    public void setBegin(int begin) {
        this.begin = begin;
    }

    public int getEnd() {
        return end;
    }

    public void setEnd(int end) {
        this.end = end;
    }

    @Override
    public int compareTo(Span span) {
        if (this.begin == span.getBegin()) {
            return this.end - span.getEnd();
        }
        return this.begin - span.getBegin();
    }

}

五、获取一个路径下的所有文件

public static List<File> getDataDirs(File topDir) {
    List<File> annFiles = new ArrayList<>();
    getAnnFilesRec(topDir, annFiles);
    return annFiles;
}

private static void getAnnFilesRec(File topDir, List<File> annFiles) {
    for (File file : topDir.listFiles()) {
        if (file.isDirectory()) {
            getAnnFilesRec(file, annFiles);
        } else {
            annFiles.add(file);
        }
    }
}

六、java 对象序列化与反序列化

// 序列化（非基础类型要实现Serializable接口，和序列号）
public static void main(String[] args) throws FileNotFoundException, IOException {
    Map<String, Integer> map = new HashMap<>();
    map.put("hi", 1);
    map.put("good", 2);
    ObjectOutputStream oo = new ObjectOutputStream(new FileOutputStream(new File("./data/serialize-test")));
    oo.writeObject(map);
    oo.close();
}

// 反序列化
@SuppressWarnings({ "rawtypes", "unchecked", "resource" })
public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
    ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("E:/Person.txt")));
    Map<String, Integer> map = (Map) ois.readObject();
    System.out.println(map.get("hi"));
}

七、java 中 OptionParser 的使用

import joptsimple.OptionParser;
import joptsimple.OptionSet;

public static  void main(String[] args) {
    OptionSet options = parseArgs(args);
    String outputFile = (String) options.valueOf("output");
    System.out.println("output: " + outputFile);
}

private static OptionSet parseArgs(String[] args) {
    OptionParser parser = new OptionParser();
    parser.accepts(OUTPUT_FILE).withOptionalArg().ofType(String.class).defaultsTo("output")
                .describedAs("result output file");
    OptionSet options = parser.parse(args);
    return options;
}

八、base64对字符串进行编码和解码

    // 编码
    String asB64 = Base64.getEncoder().encodeToString("中华人民共和国".getBytes("utf-8"));
    System.out.println(asB64); // 输出为: 5Lit5Y2O5Lq65rCR5YWx5ZKM5Zu9
    // 解码
    byte[] asBytes = Base64.getDecoder().decode("5Lit5Y2O5Lq65rCR5YWx5ZKM5Zu9");
    System.out.println(new String(asBytes, "utf-8")); // 输出为: 中华人民共和国

九、通过某个字符串将一个字符串 list 拼接起来

import org.apache.commons.lang.StringUtils;

String result = StringUtils.join(list, "\n");

十、将一个字符串写入某个文件中

import org.apache.commons.io.FileUtils;

FileUtils.writeStringToFile(new File(outputPath), text);

十一、将一个文件中的内容读出

import java.nio.file.Files;
import java.nio.file.Paths;

byte[] encoded = Files.readAllBytes(Paths.get(filePath));
String text = new String(encoded, "UTF-8");