[Java] Get the file in the jar regardless of the environment

Introduction

For example, when you want to get a text template. If the development environment and the production are different (I think it's almost different), the absolute path is environment-dependent, isn't it? You can write the location for each environment to the property, but it is better to have a small setting value, and if possible, include it in the jar. So, this time it is a utility to get the resources in the jar.

Implementation

environment

• Windows10
• Java7
• Maven

FileUtil class

FileUtil.java

package jp.demo.util;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class FileUtil {
	private static final String CHARSET_UTF8 = "UTF-8";
	private static final String LF = "\n";

	/**
	 *Return line by line in List. (Excluding line feed characters)
	 * @param string
	 * @return
	 * @throws IOException
	 */
	public static List<String> getTextLines(String string) throws IOException {
		List<String> list = new ArrayList<>();
		try (InputStream is = ClassLoader.getSystemResourceAsStream(string);
				BufferedReader br = new BufferedReader(new InputStreamReader(is, CHARSET_UTF8))) {
			String line;
			while ((line = br.readLine()) != null) {
				list.add(line);
			}
		}
		return list;
	}

	/**
	 *Return as a String. (Line feed code is LF)
	 * @param string
	 * @return
	 * @throws IOException
	 */
	public static String getTextStr(String string) throws IOException {
		StringBuilder sb = new StringBuilder();
		try (InputStream is = ClassLoader.getSystemResourceAsStream(string);
				BufferedReader br = new BufferedReader(new InputStreamReader(is, CHARSET_UTF8))) {
			String line;
			while ((line = br.readLine()) != null) {
				sb.append(line + LF);
			}
		}
		return sb.toString();
	}
}

Main class

Main.java

package jp.demo;

import java.io.IOException;
import java.util.List;

import jp.demo.util.FileUtil;

public class Main {
	public static void main(String[] args) {
		System.out.println("### START ###");
		List<String> list = null;
		String str = null;
		try {
			list = FileUtil.getTextLines("jp/demo/text1.txt");
			str = FileUtil.getTextStr("jp/demo/text1.txt");
		} catch (IOException e) {
			e.printStackTrace();
		}
		System.out.println("getTextLines:");
		list.forEach(System.out::println);
		System.out.println("\ngetTextStr:");
		System.out.println(str);

		System.out.println("### END ###");
	}
}

text file

Character code: UTF-8, line feed code: CRLF The following is saved in src / main / resources / jp / demo / text1.txt.

text1.txt

row1 test test
row2 ah
row3 Mr. Yamada

Run

Create a jar by maven install.

Execution result

I was able to get the text file with both methods.

Execution result

C:\sts\workspace\simple_maven\target>java -jar test-0.0.1-SNAPSHOT.jar
### START ###
getTextLines:
row1 test test
row2 ah
row3 Mr. Yamada

getTextStr:
row1 test test
row2 ah
row3 Mr. Yamada

### END ###

C:\sts\workspace\simple_maven\target>

This is the case when the text is saved in the character code SJIS. ↓

Execution result

C:\sts\workspace\simple_maven\target>java -jar test-0.0.1-SNAPSHOT.jar
### START ###
getTextLines:
row1 test test
row2 ??????
row3 ?R?c????

getTextStr:
row1 test test
row2 ??????
row3 ?R?c????

### END ###

C:\sts\workspace\simple_maven\target>

I read the SJIS text in UTF-8, so the characters were garbled. Then, when a character that does not exist in SJIS (the famous one is Takahashi's "Taka") is output as a file with the character set SJIS, it is replaced with "?".

Digression

On Eclipse, Maven projects are src / main / ** java **, src / main / ** resources ** However, once you build it, it will be the same, so it is the same regardless of where you save the text.

Expand the jar and jp/demo/Look under

C:\Users\xxx\Desktop\test-0.0.1-SNAPSHOT\jp\demo directory

2019/06/12  00:57    <DIR>          .
2019/06/12  00:57    <DIR>          ..
2019/06/12  00:27             1,815 Main.class
2019/06/11  01:39                26 text1.txt
2019/06/12  00:57    <DIR>          util