问题

如何在Java中将属性文件加载到Property对象中并解析属性值（`${x}`会像ant属性一样被替换）？例如使用以下属性文件：

foo=1
bar=${foo}.0

我需要将`bar`属性获取为`1.0`，而不是`${foo}.0`。有没有简单的方法来实现这个？

编辑：
Alex的解决方案适用于简单的情况。在我的情况下，我不得不解决另一个问题，导致了这个问题：[按顺序从Java属性文件中提取值？][1]。

加载和解析属性的示例代码如下：
```java
import java.util.*;
import java.io.*;
import org.apache.commons.text.StringSubstitutor;

public class Prop {
	
    Properties parsedProperties = null;

	public static Properties parseProperties(String filename) {
		// 内部辅助类用于保持属性的顺序：
		class LinkedProperties extends Properties {

			private static final long serialVersionUID = 1L;
			private final HashSet<Object> keys = new LinkedHashSet<Object>();

		    public LinkedProperties() {
		    }

		    public Iterable<Object> orderedKeys() {
		        return Collections.list(keys());
		    }

		    public Enumeration<Object> keys() {
		        return Collections.<Object>enumeration(keys);
		    }

		    public Object put(Object key, Object value) {
		        keys.add(key);
		        return super.put(key, value);
		    }
		}
		
    	LinkedProperties result = new LinkedProperties();
    	try (InputStream input = new FileInputStream(filename)) {

            result.load(input);

            @SuppressWarnings("unchecked")
            StringSubstitutor sub = new StringSubstitutor((Map) result);
            
            for (Object k : result.orderedKeys()) {
            	result.setProperty((String)k, sub.replace(result.getProperty((String)k)));
            }
        } catch (IOException ex) { ex.printStackTrace(); }

        return ((Properties)result);
    }

    public static void main(String[] args) {
    	Prop app = new Prop();
    	
	    // 测试 - 写入示例属性文件：
    	try {
	    	PrintWriter writer = new PrintWriter(new FileWriter("config.properties"));
	        writer.println("foo=1");
	        writer.println("bar=1.${foo}");
	        writer.println("baz=${bar}.0");
	        writer.println("xxx=V.${baz}");
            writer.close();
	    } catch (IOException ex) { ex.printStackTrace(); }
	    
    	// 读取并解析属性：
	    app.parsedProperties = parseProperties("config.properties");

	    // 调试打印：
        for (Object k : app.parsedProperties.keySet()) {
        	System.out.println((String)k + " = " + app.parsedProperties.getProperty((String)k));
        }
	}
}

<details>
<summary>英文:</summary>
How to load property file into Property object in Java and get property values parsed (`${x}` gets replaced as it is done for ant properties)? For example using this property file:

foo=1
bar=${foo}.0

I need to get `bar` property as `1.0` instead `${foo}.0`. Is there a easy way for this?
EDIT:
Alex's solution works for simple scenarios. In my case I had to solve another issue leading to this question: [Pulling values from a Java Properties file in order?][1]. 
Resulting sample code for loading and parsing properties:

import java.util.;
import java.io.;
import org.apache.commons.text.StringSubstitutor;

public class Prop {

Properties          parsedProperties   = null;
public static Properties parseProperties(String filename) {
// inner helper class keeping order of properties:
class LinkedProperties extends Properties {
private static final long serialVersionUID = 1L;
private final HashSet<Object> keys = new LinkedHashSet<Object>();
public LinkedProperties() {
}
public Iterable<Object> orderedKeys() {
return Collections.list(keys());
}
public Enumeration<Object> keys() {
return Collections.<Object>enumeration(keys);
}
public Object put(Object key, Object value) {
keys.add(key);
return super.put(key, value);
}
}
LinkedProperties result = new LinkedProperties();
try (InputStream input  = new FileInputStream(filename)) {
result.load(input);
@SuppressWarnings("unchecked")
StringSubstitutor sub = new StringSubstitutor((Map) result);
for (Object k : result.orderedKeys()) {
result.setProperty((String)k, sub.replace(result.getProperty((String)k)));
}
} catch (IOException ex) { ex.printStackTrace(); }
return ((Properties)result);
}
public static void main(String[] args) {
Prop app = new Prop();
// test - write sample properties file:
try {
PrintWriter writer = new PrintWriter(new FileWriter("config.properties"));
writer.println("foo=1");
writer.println("bar=1.${foo}");
writer.println("baz=${bar}.0");
writer.println("xxx=V.${baz}");
writer.close();
} catch (IOException ex) { ex.printStackTrace(); }
// read and parse properties:
app.parsedProperties = parseProperties("config.properties");
// debug print:
for (Object k : app.parsedProperties.keySet()) {
System.out.println((String)k + " = " + app.parsedProperties.getProperty((String)k));
}
}

}

[1]: https://stackoverflow.com/questions/1312383/pulling-values-from-a-java-properties-file-in-order
</details>
# 答案1
**得分**: 3
```java
// 导入必要的类和包
import org.apache.commons.text.StringSubstitutor;
// 初始化示例属性
Properties p = new Properties();
p.setProperty("foo", "${baz}.${baz}");
p.setProperty("bar", "${foo}.0");
p.setProperty("baz", "5");
Properties resolved = parseProperties(p);
System.out.println("resolved: " + resolved);
/////
public static Properties parseProperties(Properties orig) {
Properties result = new Properties();
StringSubstitutor sub = new StringSubstitutor((Map) orig);
orig.entrySet().forEach(e -> result.put(e.getKey(), sub.replace(e.getValue())));
return result;
}

输出:

resolved: {bar=5.5.0, foo=5.5, baz=5}

注意：上述内容是您提供的代码的翻译，可能会因为格式限制而略有不同。

<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-text -->
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-text</artifactId>
<version>1.8</version>
</dependency>

// init sample properties
Properties p = new Properties();
p.setProperty("foo", "${baz}.${baz}");
p.setProperty("bar", "${foo}.0");
p.setProperty("baz", "5");
Properties resolved = parseProperties(p);
System.out.println("resolved: " + resolved);
/////
public static Properties parseProperties(Properties orig) {
Properties result = new Properties();
StringSubstitutor sub = new StringSubstitutor((Map) orig);
orig.entrySet().forEach(e -> result.put(e.getKey(), sub.replace(e.getValue())));
return result;
}

resolved: {bar=5.5.0, foo=5.5, baz=5}