想象一下，你有这些属性文件“列表”：
this.is.a.key.1 = lk1mldk3ml2k3e2l3k
this.is.a.key.2 = 2309420398402931
this.is.a.key.3 = lksl1k2ml1kmd
所以...
有没有办法从属性文件中“提取”所有这些 this.is.a.key.* 键，而不必一一硬编码？
我问这个的原因是因为我不想要这个：
this.is.a.list.key = 12983798123,82193819mx91,23891293819283,3892938492834
因为我需要键名中的那些“1,2,3 ...”名称来区分一个键与另一个键。
有什么解决办法吗？还是我必须对其进行硬编码？
我写了 MapFilter 类来为我做这件事：
/*
* Note that all access through the filter reference the underlying Map so
* adding to a MapFilder results in additions to the Map.
*/
public class MapFilter<T> implements Map<String, T> {
// The enclosed map -- could also be a MapFilter.
final private Map<String, T> map;
// Use a TreeMap for predictable iteration order.
// Store Map.Entry to reflect changes down into the underlying map.
// The Key is the shortened string. The entry.key is the full string.
final private Map<String, Map.Entry<String, T>> entries = new TreeMap<String, Map.Entry<String, T>>();
// The prefix they are looking for in this map.
final private String prefix;
public MapFilter(Map<String, T> map, String prefix) {
// Store my backing map.
this.map = map;
// Record my prefix.
this.prefix = prefix;
// Build my entries.
rebuildEntries();
}
public MapFilter(Map<String, T> map) {
this(map, "");
}
private synchronized void rebuildEntries() {
// Start empty.
entries.clear();
// Build my entry set.
for (Map.Entry<String, T> e : map.entrySet()) {
String key = e.getKey();
// Retain each one that starts with the specified prefix.
if (key.startsWith(prefix)) {
// Key it on the remainder.
String k = key.substring(prefix.length());
// Entries k always contains the LAST occurrence if there are multiples.
entries.put(k, e);
}
}
}
@Override
public String toString() {
StringBuilder s = new StringBuilder("MapFilter (" + prefix + ") of " + map + " containing ").append(entrySet());
return s.toString();
}
// Constructor from a properties file.
public MapFilter(Properties p, String prefix) {
// Properties extends HashTable<Object,Object> so it implements Map.
// I need Map<String,T> so I wrap it in a HashMap for simplicity.
this(new HashMap<String, T>((Map) p), prefix);
}
// Helper to fast filter the map.
public MapFilter<T> filter(String prefix) {
// Wrap me in a new filter.
return new MapFilter<T>(this, prefix);
}
// Count my entries.
public int size() {
return entries.size();
}
// Are we empty.
public boolean isEmpty() {
return entries.isEmpty();
}
// Is this key in me?
public boolean containsKey(Object key) {
return entries.containsKey(key);
}
// Is this value in me.
public boolean containsValue(Object value) {
// Walk the values.
for (Map.Entry<String, T> e : entries.values()) {
if (value.equals(e.getValue())) {
// Its there!
return true;
}
}
return false;
}
// Get the referenced value - if present.
public T get(Object key) {
return get(key, null);
}
// Get the referenced value - if present.
public T get(Object key, T dflt) {
Map.Entry<String, T> e = entries.get((String)key);
return e != null ? e.getValue() : dflt;
}
// Add to the underlying map.
public T put(String key, T value) {
T old = null;
// Do I have an entry for it already?
Map.Entry<String, T> entry = entries.get(key);
// Was it already there?
if (entry != null) {
// Yes. Just update it.
old = entry.setValue(value);
} else {
// Add it to the map.
map.put(prefix + key, value);
// Rebuild.
rebuildEntries();
}
return old;
}
// Get rid of that one.
public T remove(Object key) {
// Do I have an entry for it?
Map.Entry<String, T> entry = entries.get((String)key);
if (entry != null) {
entries.remove(key);
// Change the underlying map.
return map.remove(prefix + key);
}
return null;
}
// Add all of them.
public void putAll(Map<? extends String, ? extends T> m) {
for (Map.Entry<? extends String, ? extends T> e : m.entrySet()) {
put(e.getKey(), e.getValue());
}
}
// Clear everything out.
public void clear() {
// Just remove mine. This does not clear the underlying map.
for (String key : entries.keySet()) {
map.remove(prefix + key);
}
entries.clear();
}
public Set<String> keySet() {
return entries.keySet();
}
public Collection<T> values() {
// Roll them all out into a new ArrayList.
List<T> values = new ArrayList<T>();
for (Map.Entry<String, T> v : entries.values()) {
values.add(v.getValue());
}
return values;
}
public Set<Map.Entry<String, T>> entrySet() {
// Roll them all out into a new TreeSet.
Set<Map.Entry<String, T>> entrySet = new TreeSet<Map.Entry<String, T>>();
for (Map.Entry<String, Map.Entry<String, T>> v : entries.entrySet()) {
entrySet.add(new Entry<T>(v));
}
return entrySet;
}
/**
* An entry.
*
* @param <T>
*
* The type of the value.
*/
private static class Entry<T> implements Map.Entry<String, T>, Comparable<Entry<T>> {
// Note that entry in the entry is an entry in the underlying map.
private final Map.Entry<String, Map.Entry<String, T>> entry;
Entry(Map.Entry<String, Map.Entry<String, T>> entry) {
this.entry = entry;
}
public String getKey() {
return entry.getKey();
}
public T getValue() {
// Remember that the value is the entry in the underlying map.
return entry.getValue().getValue();
}
public T setValue(T newValue) {
// Remember that the value is the entry in the underlying map.
return entry.getValue().setValue(newValue);
}
@Override
public boolean equals(Object o) {
if (!(o instanceof Entry)) {
return false;
}
Entry e = (Entry) o;
return getKey().equals(e.getKey()) && getValue().equals(e.getValue());
}
@Override
public int hashCode() {
return getKey().hashCode() ^ getValue().hashCode();
}
@Override
public String toString() {
return getKey() + "=" + getValue();
}
public int compareTo(Entry<T> o) {
return getKey().compareTo(o.getKey());
}
}
// Simple tests.
public static void main(String[] args) {
String[] samples = {
"Some.String.For.Me",
"Some.String.For.You",
"Some.More",
"Yet.More"};
Map map = new HashMap();
for ( String s : samples ) {
map.put(s, s);
}
Map all = new MapFilter(map);
Map some = new MapFilter(map, "Some.");
Map someString = new MapFilter(some, "String.");
System.out.println("All: "+all);
System.out.println("Some: "+some);
System.out.println("Some.String: "+someString);
}
}