用Java编写.properties文件会破坏文件的结构

问题描述

我可以使用以下代码成功写入Java .properties文件：

Properties prop = new Properties();
prop.load(input);
prop.setProperty("myProp","myValue");
prop.store(output,"");

但是当我查看.properties文件时，所有结构都消失了！字段以随机顺序编写，所有注释（花了我很多精力编写）都被覆盖了！

如何在确保结构不变的情况下写入.properties文件？

解决方法

您可以使用Apache Commons Configuration 2：

<dependency>
  <groupId>org.apache.commons</groupId>
  <artifactId>commons-configuration2</artifactId>
  <version>2.1.1</version>
</dependency>

输入文件demo.properties：

# This is the file header
#
# Lorem ipsum dolor sit amet,consectetur adipiscing elit,sed do eiusmod tempor incididunt ut labore et dolore magna
# aliqua. Ut enim ad minim veniam,quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

# Database user
db.user=admin

# Database password
db.password=password

# Database URL
db.url=localhost

# This is the file footer
#
# Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint
# occaecat cupidatat non proident,sunt in culpa qui officia deserunt mollit anim id est laborum.

演示应用程序读取，修改和写入新的属性文件：

import org.apache.commons.configuration2.PropertiesConfiguration;
import org.apache.commons.configuration2.PropertiesConfigurationLayout;
import org.apache.commons.configuration2.ex.ConfigurationException;

import java.io.*;

class PropertiesFileWithCommentsDemo {
  public static void main(String[] args) throws IOException,ConfigurationException {
    // Load existing properties file
    File file = new File("demo.properties");
    PropertiesConfiguration config = new PropertiesConfiguration();
    PropertiesConfigurationLayout layout = new PropertiesConfigurationLayout();
    layout.load(config,new InputStreamReader(new FileInputStream(file)));

    // Print some information from the properties file
    System.out.println(layout.getHeaderComment());
    System.out.println(layout.getKeys());
    System.out.println(layout.getFooterComment());

    // Change existing property
    config.setProperty("db.password","secret");

    // Add new property + comment + leading blank line
    config.setProperty("new.property","Hello world!");
    layout.setComment("new.property","This is a newly added property");
    layout.setBlancLinesBefore("new.property",1);

    // Save to new properties file
    layout.save(config,new FileWriter("demo-append.properties",false));
  }
}

控制台日志：

# This is the file header
#
# Lorem ipsum dolor sit amet,quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
[db.user,db.password,db.url]

# This is the file footer
#
# Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint
# occaecat cupidatat non proident,sunt in culpa qui officia deserunt mollit anim id est laborum.

输出文件demo-append.properties：

# This is the file header
#
# Lorem ipsum dolor sit amet,quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

# Database user
db.user=admin

# Database password
db.password=secret

# Database URL
db.url=localhost

# This is a newly added property
new.property = Hello world!

# This is the file footer
#
# Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint
# occaecat cupidatat non proident,sunt in culpa qui officia deserunt mollit anim id est laborum.