读取jar文件方式

1.ResourceLoader

Spring框架提供了Resource接口和ResourceLoader接口来方便地访问资源文件。为了更好的模拟我们实际生产中的环境，我们直接通过Controller层来对jar中的文件进行访问。

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package com.monkeybrother.spring.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;

@RestController
public class ResourcesController {
   @Autowired
   private ResourceLoader resourceLoader;

   @GetMapping("readFileFromJarWithResourceLoader")
   public void readFileFromJarWithResourceLoader() {
       try {
           Resource resource = resourceLoader.getResource("classpath:data.txt");
           try (BufferedReader reader = new BufferedReader(new InputStreamReader(resource.getInputStream(), StandardCharsets.UTF_8))) {
               String line;
               while ((line = reader.readLine()) != null) {
                   System.out.println(line);
              }
          }
      } catch (IOException e) {
           System.err.println("Error reading file from jar: " + e.getMessage());
      }
  }
}

2.getClass().getResourceAsStream()

可以直接使用getClass().getResourceAsStream()方法，这会返回一个InputStream对象。同样的把这个放在Controller中进行测试：

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@GetMapping("readFileFromJarWithResourceAsStream")
public void readFileFromJarWithResourceAsStream() {
   InputStream inputStream = getClass().getResourceAsStream("/data.txt");
   if (inputStream != null) {
       try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8))) {
           String line;
           StringBuilder contentBuilder = new StringBuilder();
           while ((line = reader.readLine()) != null) {
               contentBuilder.append(line).append("\n");
          }
           System.out.println(contentBuilder.toString());
      } catch (IOException e) {
           System.err.println("An error occurred while reading the file: " + e.getMessage());
      }
  } else {
       System.out.println("File not found: application.yml");
  }
}

3.org.springframework.util.StreamUtils

Spring框架的StreamUtils类提供了一个便捷的方法来直接读取资源内容到字符串，这样可以简化读取文件的操作：

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@GetMapping("readFileFromJarWithStreamUtils")
public void readFileFromJarWithStreamUtils() {
   try {
       Resource resource = new ClassPathResource("data.txt");
       String s = StreamUtils.copyToString(resource.getInputStream(), StandardCharsets.UTF_8);
       System.out.println(s);
  } catch (IOException e) {
       throw new RuntimeException("Failed to read file content", e);
  }
}

4. 使用 ResourcePatternResolver

**使用Spring框架的ResourcePatternResolver来读取类路径下的资源是一种更灵活的方法，它不仅允许你读取单个资源，还可以匹配和加载多个资源。**下面是一个使用ResourcePatternResolver来读取data.txt文件内容的示例：

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@GetMapping("readFileFromJarWithResourcePatternResolver")
public void readFileFromJarWithResourcePatternResolver() {
   ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
   try {
       Resource resource = resolver.getResource("data.txt");
       if (resource.exists()) {
           String content = StreamUtils.copyToString(resource.getInputStream(), StandardCharsets.UTF_8);
           System.out.println(content);
      } else {
           System.err.println("The resource 'data.txt' does not exist.");
      }
  } catch (IOException e) {
       e.printStackTrace();
  }
}

5.使用Spring Boot的ApplicationContext

Spring Boot的ApplicationContext提供了一种访问资源的方式，它允许你按名称查找资源，这在某些场景下非常有用。在使用的时候我们需要先进行组件的注入：

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@Autowired
private ResourceLoader resourceLoader;


@GetMapping("readFileFromJarWithApplicationContext")
public void readFileFromJarWithApplicationContext() {
   Resource resource = applicationContext.getResource("classpath:data.txt");
   try (InputStream inputStream = resource.getInputStream()) {
       String content = StreamUtils.copyToString(inputStream, StandardCharsets.UTF_8);
       System.out.println(content);
  } catch (IOException e) {
       e.printStackTrace();
  }
}

**需要注意这里的是applicationContext.getResource("classpath:data.txt"); 必须为 classpath:data.txt 不能简写 data.txt，**否则会报错，以下是5种方式的完整代码：

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package com.monkeybrother.spring.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.util.StreamUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;

@RestController
public class ResourcesController {
    @Autowired
    private ResourceLoader resourceLoader;
    @Autowired
    private ApplicationContext applicationContext;

    @GetMapping("readFileFromJarWithResourceLoader")
    public void readFileFromJarWithResourceLoader() {
        try {
            Resource resource = resourceLoader.getResource("classpath:data.txt");
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(resource.getInputStream(), StandardCharsets.UTF_8))) {
                String line;
                while ((line = reader.readLine()) != null) {
                    System.out.println(line);
                }
            }
        } catch (IOException e) {
            System.err.println("Error reading file from jar: " + e.getMessage());
        }
    }


    @GetMapping("readFileFromJarWithResourceAsStream")
    public void readFileFromJarWithResourceAsStream() {
        InputStream inputStream = getClass().getResourceAsStream("/data.txt");
        if (inputStream != null) {
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8))) {
                String line;
                StringBuilder contentBuilder = new StringBuilder();
                while ((line = reader.readLine()) != null) {
                    contentBuilder.append(line).append("\n");
                }
                System.out.println(contentBuilder.toString());
            } catch (IOException e) {
                System.err.println("An error occurred while reading the file: " + e.getMessage());
            }
        } else {
            System.out.println("File not found: application.yml");
        }
    }

    @GetMapping("readFileFromJarWithStreamUtils")
    public void readFileFromJarWithStreamUtils() {
        try {
            Resource resource = new ClassPathResource("data.txt");
            String s = StreamUtils.copyToString(resource.getInputStream(), StandardCharsets.UTF_8);
            System.out.println(s);
        } catch (IOException e) {
            throw new RuntimeException("Failed to read file content", e);
        }
    }


    @GetMapping("readFileFromJarWithResourcePatternResolver")
    public void readFileFromJarWithResourcePatternResolver() {
        ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        try {
            Resource resource = resolver.getResource("data.txt");
            if (resource.exists()) {
                String content = StreamUtils.copyToString(resource.getInputStream(), StandardCharsets.UTF_8);
                System.out.println(content);
            } else {
                System.err.println("The resource 'data.txt' does not exist.");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    @GetMapping("readFileFromJarWithApplicationContext")
    public void readFileFromJarWithApplicationContext() {
        Resource resource = applicationContext.getResource("classpath:data.txt");
        try (InputStream inputStream = resource.getInputStream()) {
            String content = StreamUtils.copyToString(inputStream, StandardCharsets.UTF_8);
            System.out.println(content);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


}