Question

我需要读取一个属性文件并在Java中生成一个 Properties 类。我这样做是通过使用：

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

但是，props.propertyName返回的属性不是原始属性文件的顺序。我知道 Properties 只是老式的，非泛化的Hashtables。我正在寻找一个解决方案。任何的想法？谢谢！

Answer 1

来自www.java2s.com的示例可以解决您的问题。

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;

}

您的代码将更改为：

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

Answer 2

您可以扩展属性并将所有地图方法委派给LinkedHashMap以保留订单。这是一个示例（您可能需要覆盖更多方法）：

public class LinkedProperties extends Properties{


    private static final long serialVersionUID = 1L;

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

    @Override
    public synchronized Object put(Object key, Object value){
        return linkMap.put(key, value);
    }

    @Override
    public synchronized boolean contains(Object value){
        return linkMap.containsValue(value);
    }

    @Override
    public boolean containsValue(Object value){
        return linkMap.containsValue(value);
    }

    @Override
    public synchronized Enumeration<Object> elements(){
        throw new UnsupportedOperationException(
          "Enumerations are so old-school, don't use them, "
        + "use keySet() or entrySet() instead");
    }

    @Override
    public Set<Entry<Object, Object>> entrySet(){
        return linkMap.entrySet();
    }

    @Override
    public synchronized void clear(){
        linkMap.clear();
    }

    @Override
    public synchronized boolean containsKey(Object key){
        return linkMap.containsKey(key);
    }

}

Answer 3

与上述之一类似，但没有维护我们自己的值列表的开销。我们所要做的就是维护一个单独的有序键列表，并提供一个新的“keys（）”方法。


public class SequencedProperties extends Properties {

    private static final long serialVersionUID = -7032434592318855760L;

    private List keyList = new ArrayList();

    @Override
    public synchronized Enumeration keys() {
        return Collections.enumeration(keyList);
    }

    @Override
    public synchronized Object put(Object key, Object value) {
        if (! containsKey(key)) {
            keyList.add(key);
        }

        return super.put(key, value);
    }

    @Override
    public synchronized Object remove(Object key) {
        keyList.remove(key);

        return super.remove(key);
    }

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

        super.putAll(values);
    }
}

Answer 4

您可能希望实现具有类似功能的属性类。您无法获得订单，因为正如您已经指出的那样，它使用Hashtable。

Answer 5

基于LinkedHashMap的完整实现

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("ddd","444");

        p1.put("aaa","111");
        p1.put("bbb","222");
        p1.put("ccc","333");
        p1.put("ddd","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());
    }
}

结果：

--class java.util.Properties
-- listing properties --
bbb=222
aaa=111
ddd=444
ccc=333
#comments
#Wed Apr 10 08:55:42 EEST 2013
bbb=222
aaa=111
ddd=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="ddd">444</entry>
<entry key="ccc">333</entry>
</properties>
{bbb=222, aaa=111, ddd=444, ccc=333}

--class groovy.abi.LinkedProperties
-- listing properties --
aaa=111
bbb=222
ccc=333
ddd=444
#comments
#Wed Apr 10 08:55:42 EEST 2013
aaa=111
bbb=222
ccc=333
ddd=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="ddd">444</entry>
</properties>
{aaa=111, bbb=222, ccc=333, ddd=444}

Answer 6

他们在引擎盖下被表示为Hashtable的事实意味着他们的订单不会以任何方式保留。

如果你非常渴望这项功能，我建议你“推出自己的”属性读者。

Answer 7

正确实施keySet：

public class OrderedProperties extends Properties {

  private Set<Object> keySet = new LinkedHashSet<Object>(100);

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

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

  @Override
  public synchronized Object put(Object key, Object value) {
    if (! keySet.contains(key)) {
        keySet.add(key);
    }
    return super.put(key, value);
  }

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

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

Answer 8

子类属性用于记忆阅读顺序并创建使用有序键列表的枚举？

Answer 9

解决问题：“根据属性文件中的顺序执行类。”我通常使用两种可能之一：

1 - 使用一个属性作为逗号分隔列表，其中包含类名或类定义的键

loadClasses = class-definition-A，class-definition-B，class-definition-C

或（如果“定义”由多个属性组成，则有用）

loadClasses = keyA，keyB，keyC
    keyA = class-definition-A
    keyB = class-definition-B
    keyC = class-definition-C

2 - 使用键后跟索引（计数器）。在循环中读取键，直到找不到值。

class1 = class-definition-A
    class2 = class-definition-B
    class3 = class-definition-C

如何以原始顺序读取java中的属性文件

9 个答案: