Question

如何在读取属性文件时保留有序插入？

这个问题是自我解释的。阅读属性文件很好。但是此示例编码保留属性文件中所有属性的读取和插入顺序的方式。辅助类只是扩展属性，并在内部使用Linked Hash Map来保留插入顺序。

Answer 1

让我们编写一个自定义类而不是使用java.util.Properties，我们的代码将管理所有内容：读取属性文件，拆分键值对，维护文件中出现的属性顺序等这是一个示例代码：

package com.test;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Scanner;

public class CustomProperty {

    public static void main(String[] args) {
        Map<String, String> properties = parse("test.properties");
        System.out.println(properties);
    }

    public static Map<String, String> parse(String filePath) {
        Map<String, String> properties = new LinkedHashMap<>();
        Scanner sc;
        try {
            sc = new Scanner(new File(filePath));
            while (sc.hasNextLine()) {
                try {
                    String[] tokens = sc.nextLine().split("=");
                    properties.put(tokens[0].trim(), tokens[1].trim());
                } catch (Exception e) {
                }
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return properties;
    }

}

Answer 2

    **application.properties**

    banner.charset=UTF-8
    banner.location=classpath:banner.txt

    server.port=8080
    server.contextPath=/test
    spring.mvc.view.prefix: /WEB-INF/jsp/
    spring.mvc.view.suffix: .jsp

    server.session.timeout=18000
    server.session.cookie.max-age=18000
    management.security.enabled=false
    security.basic.enabled=false
    a=1
    b=2

    import java.io.IOException;
    import java.io.InputStream;
    import java.util.Collections;
    import java.util.Enumeration;
    import java.util.LinkedHashMap;
    import java.util.Map;
    import java.util.Properties;
    import java.util.Set;

    // Load and Read a property file from class path

    public class Load_and_Print_a_Property_File_From_Classpath2 {

        public static void main(String[] args) {

            PreserveInsertionOrderedProperties prop = new PreserveInsertionOrderedProperties();
            InputStream input = null;
            String filename = "application.properties";
            try {

                input = Load_and_Print_a_Property_File_From_Classpath2.class.getClassLoader().getResourceAsStream(filename);
                if (input == null) {
                    System.out.println("Sorry, unable to find " + filename);
                    return;
                }
                prop.load(input);

                LinkedHashMap<Object, Object> keyValueSet = prop.keyValueSet;
                for (Object key : keyValueSet.keySet()) {
                    System.out.println("Key = " + key + " | " + "Value = " + keyValueSet.get(key));
                }


            } catch (IOException ex) {
                ex.printStackTrace();
            } finally {
                if (input != null) {
                    try {
                        input.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public class PreserveInsertionOrderedProperties extends Properties {

        private static final long serialVersionUID = 1L;

        public LinkedHashMap<Object, Object> keyValueSet = new LinkedHashMap<Object, Object>();

        @Override
        public Enumeration<Object> keys() {
            return Collections.enumeration(keyValueSet.keySet());
        }

        @Override
        public Set<Object> keySet() {
            return keyValueSet.keySet();
        }

        @Override
        public synchronized Object put(Object key, Object value) {
            if (!keyValueSet.containsValue(key)) 
                keyValueSet.put(key.toString(), value.toString());
            return keyValueSet.get(key);
        }

        @Override
        public synchronized Object remove(Object key) {
            return keyValueSet.remove(key);
        }

        @Override
        public synchronized void putAll(Map values) {
            for (Object key : values.keySet()) {
                if (!containsKey(key)) {
                    keyValueSet.putAll(values);
                }
            }
        }
    }

    **After print**

    Key = banner.charset | Value = UTF-8

    Key = banner.location | Value = classpath:banner.txt

    Key = server.port | Value = 8080

    Key = server.contextPath | Value = /test

    Key = spring.mvc.view.prefix | Value = /WEB-INF/jsp/

    Key = spring.mvc.view.suffix | Value = .jsp

    Key = server.session.timeout | Value = 18000

    Key = server.session.cookie.max-age | Value = 18000

    Key = management.security.enabled | Value = false

    Key = security.basic.enabled | Value = false

    Key = a | Value = 1

    Key = b | Value = 2

如何在读取属性文件时保留有序插入？

2 个答案: