FilterWriter (Java SE 22 & JDK 22) の使い方まとめです。
ほとんどのメソッドにサンプルコードがあります。
API仕様書のおともにどうぞ。
概要
フィルタ処理された文字ストリームのための抽象クラスです。 抽象クラスFilterWriterそのものが、格納されているストリームにすべての要求を渡すデフォルトのメソッドを提供します。 FilterWriterのサブクラスは、これらのメソッドの一部をオーバーライドし、追加のメソッドやフィールドを提供することもできます。
FilterWriter は、Writer オブジェクトをラップするだけのクラスです。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var sw = new StringWriter();
try (final var writer = new MyWriter(sw)) {
writer.write("abcd");
writer.write('-');
writer.write("XYZ");
}
System.out.println(sw); // abcd-XYZ
フィールド
protected Writer out
ベースとなる文字出力ストリームです。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
Writer getOut() {
return out;
}
}
final var sw = new StringWriter();
try (final var writer = new MyWriter(sw)) {
System.out.println(writer.getOut() == sw); // true
}
Writerで宣言されたフィールド
lock
「Java API 使用例 : Writer」をご参照ください。
コンストラクタ
FilterWriter (Writer out)
フィルタ処理された新しいライターを作成します。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var sw = new StringWriter();
try (final var writer = new MyWriter(sw)) {
writer.write("abcd");
writer.write("XYZ");
}
System.out.println(sw); // abcdXYZ
メソッド
void close ()
ストリームを最初にフラッシュして、閉じます。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
try (final var writer = new MyWriter(Files.newBufferedWriter(path))) {
writer.append("abcd");
}
final var str = Files.readString(path);
System.out.println(str); // abcd
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
// try-with-resources文を使わない例です。
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
final var writer = new MyWriter(Files.newBufferedWriter(path));
try {
writer.append("abcd");
} finally {
writer.close();
}
final var str = Files.readString(path);
System.out.println(str); // abcd
void flush ()
ストリームをフラッシュします。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var sw = new StringWriter();
try (final var writer = new MyWriter(new BufferedWriter(sw, 128))) {
writer.write("abcdXYZ");
System.out.println(sw.toString().isEmpty()); // true
writer.flush();
System.out.println(sw); // abcdXYZ
}
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var sw = new StringWriter();
try (final var writer = new MyWriter(new BufferedWriter(sw, 4))) {
writer.write("abcdXYZ");
System.out.println(sw); // abcd
writer.flush();
System.out.println(sw); // abcdXYZ
}
void write (char[] cbuf, int off, int len)
文字の配列の一部を書き込みます。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final char[] cbuf = {'a', 'b', 'c', 'd'};
final var sw1 = new StringWriter();
try (final var writer = new MyWriter(sw1)) {
writer.write(cbuf, 0, 1);
}
System.out.println(sw1); // a
final var sw2 = new StringWriter();
try (final var writer = new MyWriter(sw2)) {
writer.write(cbuf, 0, 2);
}
System.out.println(sw2); // ab
final var sw3 = new StringWriter();
try (final var writer = new MyWriter(sw3)) {
writer.write(cbuf, 0, 3);
}
System.out.println(sw3); // abc
final var sw4 = new StringWriter();
try (final var writer = new MyWriter(sw4)) {
writer.write(cbuf, 0, 4);
}
System.out.println(sw4); // abcd
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final char[] cbuf = {'a', 'b', 'c', 'd'};
final var sw1 = new StringWriter();
try (final var writer = new MyWriter(sw1)) {
writer.write(cbuf, 0, 4);
}
System.out.println(sw1); // abcd
final var sw2 = new StringWriter();
try (final var writer = new MyWriter(sw2)) {
writer.write(cbuf, 1, 3);
}
System.out.println(sw2); // bcd
final var sw3 = new StringWriter();
try (final var writer = new MyWriter(sw3)) {
writer.write(cbuf, 2, 2);
}
System.out.println(sw3); // cd
final var sw4 = new StringWriter();
try (final var writer = new MyWriter(sw4)) {
writer.write(cbuf, 3, 1);
}
System.out.println(sw4); // d
void write (int c)
単一の文字を書き込みます。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var sw = new StringWriter();
try (final var writer = new MyWriter(sw)) {
writer.write('a');
writer.write('b');
writer.write('c');
writer.write('d');
writer.write('X');
writer.write('Y');
writer.write('Z');
}
System.out.println(sw); // abcdXYZ
void write (String str, int off, int len)
文字列の一部を書き込みます。
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var str = "abcd";
final var sw1 = new StringWriter();
try (final var writer = new MyWriter(sw1)) {
writer.write(str, 0, 1);
}
System.out.println(sw1); // a
final var sw2 = new StringWriter();
try (final var writer = new MyWriter(sw2)) {
writer.write(str, 0, 2);
}
System.out.println(sw2); // ab
final var sw3 = new StringWriter();
try (final var writer = new MyWriter(sw3)) {
writer.write(str, 0, 3);
}
System.out.println(sw3); // abc
final var sw4 = new StringWriter();
try (final var writer = new MyWriter(sw4)) {
writer.write(str, 0, 4);
}
System.out.println(sw4); // abcd
class MyWriter extends FilterWriter {
MyWriter(Writer out) {
super(out);
}
}
final var str = "abcd";
final var sw1 = new StringWriter();
try (final var writer = new MyWriter(sw1)) {
writer.write(str, 0, 4);
}
System.out.println(sw1); // abcd
final var sw2 = new StringWriter();
try (final var writer = new MyWriter(sw2)) {
writer.write(str, 1, 3);
}
System.out.println(sw2); // bcd
final var sw3 = new StringWriter();
try (final var writer = new MyWriter(sw3)) {
writer.write(str, 2, 2);
}
System.out.println(sw3); // cd
final var sw4 = new StringWriter();
try (final var writer = new MyWriter(sw4)) {
writer.write(str, 3, 1);
}
System.out.println(sw4); // d
Writerで宣言されたメソッド
append, append, append, nullWriter, write, write
「Java API 使用例 : Writer」をご参照ください。