How to read a properties file in java in the origi

Question

This question already has an answer here:

• Pulling values from a Java Properties file in order? 14 answers

I need to read a properties file and generate a Properties class in Java. I do so by using:

Properties props = new Properties();
props.load(new FileInputStream(args[0]));
for (Enumeration e = props.propertyNames(); e.hasMoreElements();) {
}

However, the properties returned by props.propertyName is not in the order of the original properties file. I understand that Properties are just old fashioned, non-generified Hashtables. I'm looking for a work around. Any idea? Thank you!

Answer 1

full implementation based on LinkedHashMap

import java.util.*;
import java.io.*;

/**
 * Ordered properties implementation
*/

public class LinkedProperties extends Properties{
    private static final long serialVersionUID = 1L;

    private Map<Object, Object> linkMap = new LinkedHashMap<Object,Object>();

    public void clear(){
        linkMap.clear();
    }
    public boolean contains(Object value){
        return linkMap.containsValue(value);
    }
    public boolean containsKey(Object key){
        return linkMap.containsKey(key);
    }
    public boolean containsValue(Object value){
        return linkMap.containsValue(value);
    }
    public Enumeration elements(){
        throw new RuntimeException("Method elements is not supported in LinkedProperties class");
    }
    public Set entrySet(){
        return linkMap.entrySet();
    }
    public boolean equals(Object o){
        return linkMap.equals(o);
    }
    public Object get(Object key){
        return linkMap.get(key);
    }
    public String getProperty(String key) {
        Object oval = get(key); //here the class Properties uses super.get()
        if(oval==null)return null;
        return (oval instanceof String) ? (String)oval : null; //behavior of standard properties
    }
    public boolean isEmpty(){
        return linkMap.isEmpty();
    }
    public  Enumeration keys(){
        Set keys=linkMap.keySet();
        return Collections.enumeration(keys);
    }
    public Set keySet(){
        return linkMap.keySet();
    }
    public void list(PrintStream out) {
        this.list(new PrintWriter(out,true));
    }
    public void list(PrintWriter out) {
        out.println("-- listing properties --");
        for (Map.Entry e : (Set<Map.Entry>)this.entrySet()){
            String key = (String)e.getKey();
            String val = (String)e.getValue();
            if (val.length() > 40) {
                val = val.substring(0, 37) + "...";
            }
            out.println(key + "=" + val);
        }
    }

    public Object put(Object key, Object value){
        return linkMap.put(key, value);
    }
    public int size(){
        return linkMap.size();
    }
    public Collection values(){
        return linkMap.values();
    }

    //for test purpose only
    public static void main(String[] arg)throws Exception{
        Properties p0=new Properties();
        Properties p1=new LinkedProperties();
        p0.put("aaa","111");
        p0.put("bbb","222");
        p0.put("ccc","333");
        p0.put("ffffd","444");

        p1.put("aaa","111");
        p1.put("bbb","222");
        p1.put("ccc","333");
        p1.put("ffffd","444");

        System.out.println("\n--"+p0.getClass());
        p0.list(System.out);
        p0.store(System.out,"comments");
        p0.storeToXML(System.out,"comments");
        System.out.println(p0.toString());

        System.out.println("\n--"+p1.getClass());
        p1.list(System.out);
        p1.store(System.out,"comments");
        p1.storeToXML(System.out,"comments");
        System.out.println(p1.toString());
    }
}

Result:

--class java.util.Properties
-- listing properties --
bbb=222
aaa=111
ffffd=444
ccc=333
#comments
#Wed Apr 10 08:55:42 EEST 2013
bbb=222
aaa=111
ffffd=444
ccc=333
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
<comment>comments</comment>
<entry key="bbb">222</entry>
<entry key="aaa">111</entry>
<entry key="ffffd">444</entry>
<entry key="ccc">333</entry>
</properties>
{bbb=222, aaa=111, ffffd=444, ccc=333}

--class groovy.abi.LinkedProperties
-- listing properties --
aaa=111
bbb=222
ccc=333
ffffd=444
#comments
#Wed Apr 10 08:55:42 EEST 2013
aaa=111
bbb=222
ccc=333
ffffd=444
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
<comment>comments</comment>
<entry key="aaa">111</entry>
<entry key="bbb">222</entry>
<entry key="ccc">333</entry>
<entry key="ffffd">444</entry>
</properties>
{aaa=111, bbb=222, ccc=333, ffffd=444}

Answer 2

Example from www.java2s.com should solve your problem.

import java.util.Enumeration;
import java.util.Properties;
import java.util.Vector;

/**
 * <a href="OrderedProperties.java.html"><b><i>View Source</i></b></a>
 *
 * @author Brian Wing Shun Chan
 *
 */
public class OrderedProperties extends Properties {

    public OrderedProperties() {
        super ();

        _names = new Vector();
    }

    public Enumeration propertyNames() {
        return _names.elements();
    }

    public Object put(Object key, Object value) {
        if (_names.contains(key)) {
            _names.remove(key);
        }

        _names.add(key);

        return super .put(key, value);
    }

    public Object remove(Object key) {
        _names.remove(key);

        return super .remove(key);
    }

    private Vector _names;

}

And your code will change to:

Properties props = new OrderedProperties();
props.load(new FileInputStream(args[0]));
for (Enumeration e = props.propertyNames(); e.hasMoreElements();) {
}

Answer 3

Subclass Properties to memorize reading order and create an Enumeration that uses the ordered keys list ?