3
UPDATE2：我自己的適配器類版本，它只在構造函數中調用instanceof，並在flush()和close()函數中使用（Java 1.5）增量（避免在對象構造之後需要任何反射或邏輯），包含在這篇文章的底部。 UPDATE1：馬克Baumbach寫了一個簡單的適配器，正是我所需要的。包括在下面。原來的問題如下。如何將java.lang.Appendable包裝到java.io.Writer中？
，需要一個java.lang.Appendable可以接受java.io.Writer，因爲Writer實現Appendable的功能。
另一種方式呢？我正在使用一個需要編寫器的函數，並且我正在嘗試創建另一個調用它的函數，它接受一個appendable並將它傳遞給原始編寫器函數。
我看到您可以擴展Writer，這是抽象的，並將所有write(...)函數重定向到其對應的append(...) -s。但是你也必須實現flush()和close()，並且我很清楚如何將它們寫得乾乾淨淨，以便這個包裝類可以接受任何可追加。
我很驚訝沒有任何東西已經存在，無論是在web或stackoverflow中，還是在現有的庫中，解決這個問題。至少不是我能找到的。
我希望在這裏有一點指導。謝謝。
回答此問題的適配器代碼。寫由馬克·鮑姆巴赫（我自己的版本低於）：
import java.io.Closeable;
import java.io.Flushable;
import java.io.IOException;
import java.io.Writer;
public class AppendableWriterAdapter extends Writer {
private Appendable appendable;
public AppendableWriterAdapter(Appendable appendable) {
this.appendable = appendable;
}
@Override
public void write(char[] cbuf, int off, int len) throws IOException {
appendable.append(String.valueOf(cbuf), off, len);
}
@Override
public void flush() throws IOException {
if (appendable instanceof Flushable) {
((Flushable) appendable).flush();
}
}
@Override
public void close() throws IOException {
flush();
if (appendable instanceof Closeable) {
((Closeable) appendable).close();
}
}
}
這是我自己的版本的基礎上，Marc的，那也只是在構造函數中使用instanceof，並且在flush()一（Java 1.5中）三角洲和close()。這是爲了避免在對象構造之後使用任何邏輯或反射。這也被釋放爲gist：https://gist.github.com/aliteralmind/8494917
這個類包含了演示，後面兩個什麼也不做的增量（一個Flushable，一個Closeable），主要功能（newWriterForAppendable(apbl)），然後將適配器類本身。
import java.io.Closeable;
import java.io.Flushable;
import java.io.IOException;
import java.io.Writer;
/**
<P>{@code java NewWriterForAppendable}.</P>
**/
public class NewWriterForAppendable {
/**
<P>Demonstrates {@code newWriterForAppendable(apbl)} for creating a new {@code Writer} that wraps around {@code System.out} (writes to the console).</P>
**/
public static final void main(String[] igno_red) {
try {
NewWriterForAppendable.newWriterForAppendable(System.out).write("hello");
} catch(IOException iox) {
throw new RuntimeException("WriterForAppendableXmpl", iox);
}
}
/**
<P>A {@code Flushable} whose {@code flush()} function does nothing. This is used by {@link #newWriterForAppendable(Appendable ap_bl) newWriterForAppendable}{@code (apbl)} as a (Java 1.5) delta.</P>
@see #newWriterForAppendable(Appendable) newWriterForAppendable(apbl)
**/
public static final Flushable FLUSHABLE_DO_NOTHING = new Flushable() {
public void flush() {
}
};
/**
<P>A {@code Closeable} whose {@code close()} function does nothing. This is used by {@link #newWriterForAppendable(Appendable ap_bl) newWriterForAppendable}{@code (apbl)} as a (Java 1.5) delta.</P>
@see #newWriterForAppendable(Appendable) newWriterForAppendable(apbl)
**/
public static final Closeable CLOSEABLE_DO_NOTHING = new Closeable() {
public void close() {
}
};
/**
<P>Creates a new {@code java.io.Writer} that wraps around a {@code java.lang.Appendable}. It properly {@link java.io.Writer#flush() flush}es and {@link java.io.Writer#close() close}s appendables that happened to also be {@link java.io.Flushable}s and/or {@link java.io.Closeable Closeable}s. This uses {@code instanceof} only in the constructor, and a delta in {@code flush()} and {@code close()}, which avoids having to use any logic or reflection after object construction.</P>
<P>This function is released as a <A HREF="https://gist.github.com/aliteralmind/8494917">gist</A>, and is an example of the <A HREF="http://en.wikipedia.org/wiki/Adapter_pattern#Object_Adapter_pattern">Object Adapter pattern</A>. Thanks to <A HREF="http://stackoverflow.com/users/1211906/marc-baumbach">Marc Baumbach</A> on <A HREF="http://stackoverflow.com">{@code stackoverflow}</A> for the assistance. See (viewed 1/18/2014)
<BR> <CODE><A HREF="http://stackoverflow.com/questions/21200421/how-to-wrap-a-java-lang-appendable-into-a-java-io-writer">http://stackoverflow.com/questions/21200421/how-to-wrap-a-java-lang-appendable-into-a-java-io-writer</A></CODE></P>
@return A new writer that uses an appendable to do its output.
@see #FLUSHABLE_DO_NOTHING
@see #CLOSEABLE_DO_NOTHING
**/
public static final Writer newWriterForAppendable(Appendable ap_bl) {
return (new WFA(ap_bl));
}
private NewWriterForAppendable() {
throw new IllegalStateException("constructor: Do not instantiate.");
}
}
class WFA extends Writer {
private final Appendable apbl;
private final Flushable flbl;
private final Closeable clbl;
public WFA(Appendable ap_bl) {
if(ap_bl == null) {
throw new NullPointerException("ap_bl");
}
apbl = ap_bl;
//Avoids instanceof at every call to flush() and close()
flbl = (Flushable)((ap_bl instanceof Flushable) ? ap_bl
: NewWriterForAppendable.FLUSHABLE_DO_NOTHING);
clbl = (Closeable)((ap_bl instanceof Closeable) ? ap_bl
: NewWriterForAppendable.CLOSEABLE_DO_NOTHING);
}
@Override
public void write(char[] a_c, int i_ndexStart, int i_ndexEndX) throws IOException {
apbl.append(String.valueOf(a_c), i_ndexStart, i_ndexEndX);
}
@Override
public Writer append(char c_c) throws IOException {
apbl.append(c_c);
return this;
}
@Override
public Writer append(CharSequence c_q) throws IOException {
apbl.append(c_q);
return this;
}
@Override
public Writer append(CharSequence c_q, int i_ndexStart, int i_ndexEndX) throws IOException {
apbl.append(c_q, i_ndexStart, i_ndexEndX);
return this;
}
@Override
public void flush() throws IOException {
flbl.flush();
}
@Override
public void close() throws IOException {
flush();
clbl.close();
}
}
Nitpick：對於'write（char []，int，int）'的impl，使用'apbl.append（String.valueOf（a_c， i_ndexStart，i_ndexEndX））;'而不是'apbl.append（String.valueOf（a_c），i_ndexStart，i_ndexEndX）;'？我認爲這會減少在start＆end不是'0'和'a_c.length'的情況下複製的字節數。 – kevinarpe
使用'CharBuffer.wrap（cbuf，off，len）'而不是'String.valueOf（cbuf，off，len）'會更高效，因爲這會爲現有的'cbuf'創建一個視圖，完全可以創建一個「CharSequence」。 – toKrause