从Jar包读取文件内容

前提

文件目录如下

/src
    /main
        /java
        /resources
            /mydata.txt

目标文件： mydata.txt

如何方便读取该文件内容

1. 将文件读取为InputStream

2. 从文件读取内容

下面展示了读取文件内容的示例工具

注意：如果文件内容过大，不要使用该工具，应该自己手动处理inputStream.

使用Spring方式

import org.apache.commons.io.IOUtils;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;

@Component
public class ResourceHelper {
    @Autowired
    private ResourceLoader resourceLoader;

    /**
    * 读取文件内容为一整个字符串
    */
    public String readString(String resourcePath) throws IOException {
        Resource resource = resourceLoader.getResource(resourcePath);
        InputStream inputStream = resource.getInputStream();

		return IOUtils.toString(inputStream, StandardCharsets.UTF_8.name());
    }

    /**
    * 读取文件内容为列表
    */
    public List<String> readLines(String resourcePath) throws IOException {
        Resource resource = resourceLoader.getResource(resourcePath);
        InputStream inputStream = resource.getInputStream();

        return IOUtils.readLines(inputStream, StandardCharsets.UTF_8.name());
    }
}

使用示例

// 导入上面的ResourceHelper
import xxx.ResourceHelper;
import org.springframework.util.ResourceUtils;

@Component
public class TestDAO {
    // 注意，此处添加文件名前缀
    public static final String SQL_PATH = ResourceUtils.CLASSPATH_URL_PREFIX
    										 + "mydata.txt";

    @Autowired
    private ResourceHelper resourceHelper;

    public Object search(String structuredId) throws IOException {
        String sql = resourceHelper.readString(SQL_PATH);

        // ... 省略处理方式
    }
}

不使用Spring的方式

1. 编写ClassUtils

   public class ClassUtils {
       public static ClassLoader getDefaultClassLoader() {
            ClassLoader cl = null;
            try {
                   // 获取当前线程classLoader
                    cl = Thread.currentThread().getContextClassLoader();
            }
            catch (Throwable ex) {
                    // Cannot access thread context ClassLoader - falling back...
            }
            if (cl == null) {
                    // No thread context class loader -> use class loader of this class.
                   // 获取当前类ClassLoader
                    cl = ClassUtils.class.getClassLoader();
                    if (cl == null) {
                            // getClassLoader() returning null indicates the bootstrap ClassLoader
                            try {
                                   // 获取系统默认ClassLoader
                                    cl = ClassLoader.getSystemClassLoader();
                            }
                            catch (Throwable ex) {
                                    // Cannot access system ClassLoader - oh well, maybe the caller can live with null...
                            }
                    }
            }
            return cl;
        }
   }
   

2. 编写工具类

   import org.apache.commons.io.IOUtils;
   
   public class ResourceUtils {
   
       public String readString(String resourcePath) throws IOException {
           InputStream inputStream = ClassUtils.getDefaultClassLoader()
                                           .getResourceAsStream(resourcePath);
   
           return IOUtils.toString(inputStream, StandardCharsets.UTF_8.name());
       }
   
       public List<String> readLine(String resourcePath) throws IOException {
           InputStream inputStream = ClassUtils.getDefaultClassLoader()
                                           .getResourceAsStream(resourcePath);
   
           return IOUtils.readLines(inputStream, StandardCharsets.UTF_8.name());
       }
   }
   

3. 使用

   @Component
   public class TestDAO {
       // 此处直接写文件名
       public static final String SQL_PATH = "mydata.txt";
   
       public Object search(String structuredId) throws IOException {
           String sql = ResourceUtils.readString(SQL_PATH);
   
           // ... 省略处理方式
       }
   }