java - 如何从 META-INF 目录加载属性文件？

Question

正在运行的 JAR 执行中使用的 properties 文件最好属于 META-INF 是否正确？符合标准目录布局的概念 specified通过 Maven。

假设需要该结构，properties 文件是如何从 META-INF 加载的？

thufir@doge:~/NetBeansProjects/json_parser$ 
thufir@doge:~/NetBeansProjects/json_parser$ java -jar build/libs/json_parser-all.jarAug 18, 2017 6:44:24 AM net.bounceme.doge.json.Main main
INFO: starting
Aug 18, 2017 6:44:24 AM net.bounceme.doge.json.Main run
INFO: actually
Aug 18, 2017 6:44:24 AM net.bounceme.doge.json.PropertiesReader tryGetProps
INFO: properties
Aug 18, 2017 6:44:24 AM net.bounceme.doge.json.PropertiesReader getProps
INFO: properties
Exception in thread "main" java.lang.NullPointerException
    at java.util.Properties$LineReader.readLine(Properties.java:434)
    at java.util.Properties.load0(Properties.java:353)
    at java.util.Properties.load(Properties.java:341)
    at net.bounceme.doge.json.PropertiesReader.getProps(PropertiesReader.java:26)
    at net.bounceme.doge.json.PropertiesReader.tryGetProps(PropertiesReader.java:16)
    at net.bounceme.doge.json.Main.run(Main.java:18)
    at net.bounceme.doge.json.Main.main(Main.java:12)
thufir@doge:~/NetBeansProjects/json_parser$ 
thufir@doge:~/NetBeansProjects/json_parser$ jar tf build/libs/json_parser-all.jarMETA-INF/
META-INF/MANIFEST.MF
META-INF/maven/
META-INF/maven/javax.json/
META-INF/maven/javax.json/javax.json-api/
META-INF/maven/javax.json/javax.json-api/pom.properties
META-INF/maven/javax.json/javax.json-api/pom.xml
javax/
javax/json/
javax/json/Json.class
javax/json/JsonArray.class
javax/json/JsonArrayBuilder.class
javax/json/JsonBuilderFactory.class
javax/json/JsonException.class
javax/json/JsonMergePatch.class
javax/json/JsonNumber.class
javax/json/JsonObject.class
javax/json/JsonObjectBuilder.class
javax/json/JsonPatch$Operation.class
javax/json/JsonPatch.class
javax/json/JsonPatchBuilder.class
javax/json/JsonPointer.class
javax/json/JsonReader.class
javax/json/JsonReaderFactory.class
javax/json/JsonString.class
javax/json/JsonStructure.class
javax/json/JsonValue$ValueType.class
javax/json/JsonValue.class
javax/json/JsonValueImpl.class
javax/json/JsonWriter.class
javax/json/JsonWriterFactory.class
javax/json/spi/
javax/json/spi/JsonProvider.class
javax/json/stream/
javax/json/stream/JsonCollectors.class
javax/json/stream/JsonGenerationException.class
javax/json/stream/JsonGenerator.class
javax/json/stream/JsonGeneratorFactory.class
javax/json/stream/JsonLocation.class
javax/json/stream/JsonParser$Event.class
javax/json/stream/JsonParser.class
javax/json/stream/JsonParserFactory.class
javax/json/stream/JsonParsingException.class
module-info.class
net/
net/bounceme/
net/bounceme/doge/
net/bounceme/doge/json/
net/bounceme/doge/json/Main.class
net/bounceme/doge/json/Marshaller.class
net/bounceme/doge/json/PropertiesReader.class
net/bounceme/doge/json/JsonReader.class
json.json
properties.properties
META-INF/properties.properties
thufir@doge:~/NetBeansProjects/json_parser$ 
thufir@doge:~/NetBeansProjects/json_parser$ jar tf build/libs/json_parser-all.jar | grep properties.properties
properties.properties
META-INF/properties.properties
thufir@doge:~/NetBeansProjects/json_parser$ 

及相关代码:

package net.bounceme.doge.json;

import java.io.IOException;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;

public class PropertiesReader {

    private static final Logger log = Logger.getLogger(PropertiesReader.class.getName());

    public Properties tryGetProps(String propertiesFileName) {
        log.info(propertiesFileName);
        Properties properties = new Properties();
        try {
            properties = getProps(propertiesFileName);
        } catch (IOException ex) {
            Logger.getLogger(PropertiesReader.class.getName()).log(Level.SEVERE, null, ex);
        }
        return properties;
    }

    private Properties getProps(String propertiesFileName) throws IOException {
        log.info(propertiesFileName);
        Properties properties = new Properties();
        properties.load(PropertiesReader.class.getResourceAsStream("/META-INF/" + propertiesFileName));
        log.info(properties.toString());
        return properties;
    }
}

这是在relation从 gradle 和基于 general 正确使用 init信息。

我尝试删除前导 / 作为 suggested -- 结果同上。

Answer 1

您没有义务将您的属性文件存储在 META-INF 中，事实上，这样做甚至不是很常见(至少以我的经验而言)。为支持这一论点，Java JAR Specification在 META-INF 的预期内容中不包含属性文件。

下面的代码显示了从 JAR 加载属性的几种方法，无论它们是否在 META-INF 中。

给定一个包含以下内容的 JAR 文件:

jar -tvf properties.jar
   0 Fri Aug 18 15:35:52 IST 2017 META-INF/
  68 Fri Aug 18 15:35:52 IST 2017 META-INF/MANIFEST.MF
   4 Fri Aug 18 15:35:32 IST 2017 META-INF/bProps.properties
   4 Fri Aug 18 15:35:18 IST 2017 aProps.properties

您可以像这样加载 aProps.properties 和 bProps.properties:

@Test
public void canWriteAndRead() throws IOException {
    ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
    // this works
    loadProperties(systemClassLoader.getResource("aProps.properties"));
    // this works
    loadProperties(systemClassLoader.getResource("META-INF/bProps.properties"));
    // this does not work
    loadProperties(systemClassLoader.getResource("/aProps.properties"));
    // this does not work
    loadProperties(systemClassLoader.getResource("/META-INF/bProps.properties"));

    ClassLoader classLoader = getClass().getClassLoader();
    // this works
    loadProperties(classLoader.getResource("aProps.properties"));
    // this works
    loadProperties(classLoader.getResource("META-INF/bProps.properties"));
    // this does not work
    loadProperties(classLoader.getResource("/aProps.properties"));
    // this does not work
    loadProperties(classLoader.getResource("/META-INF/bProps.properties"));

    // this works
    loadProperties(getClass().getResourceAsStream("/aProps.properties"));
    // this works
    loadProperties(getClass().getResourceAsStream("/META-INF/bProps.properties"));
    // this does not work
    loadProperties(getClass().getResourceAsStream("aProps.properties"));
    // this does not work
    loadProperties(getClass().getResourceAsStream("META-INF/bProps.properties"));
}

private void loadProperties(InputStream incoming) throws IOException {
    if (incoming != null) {
        Properties properties = new Properties();
        properties.load(incoming);
        for (String s : properties.stringPropertyNames()) {
            System.out.println(s);
        }
    }
}

private void loadProperties(URL incoming) throws IOException {
    if (incoming != null) {
        Properties properties = new Properties();
        properties.load(incoming.openStream());
        for (String s : properties.stringPropertyNames()) {
            System.out.println(s);
        }
    }
}