如果您有java.io.InputStream对象，应该如何处理该对象并生成String？
假设我有一个包含文本数据的InputStream，我想将其转换为String，例如，我可以将其写入日志文件。
获取InputStream并将其转换为字符串的最简单方法是什么？
public String convertStreamToString(InputStream is) {
// ???
}
当前回答
为了完整起见，这里是Java 9解决方案：
public static String toString(InputStream input) throws IOException {
return new String(input.readAllBytes(), StandardCharsets.UTF_8);
}
这使用添加到Java9中的readAllBytes方法。
其他回答
我在这里对14个不同的答案做了一个基准测试（很抱歉没有提供学分，但有太多重复）。
结果非常令人惊讶。事实证明，Apache IOUtils是最慢的解决方案，ByteArrayOutputStream是最快的解决方案：
因此，首先是最好的方法：
public String inputStreamToString(InputStream inputStream) throws IOException {
try(ByteArrayOutputStream result = new ByteArrayOutputStream()) {
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) != -1) {
result.write(buffer, 0, length);
}
return result.toString(UTF_8);
}
}
20个周期内20 MB随机字节的基准结果
时间（毫秒）
字节数组输出流测试：194NioStream:198Java9ISTransferTo:201Java9ISReadAllBytes:205缓冲输入流VsByteArray输出流：314ApacheStringWriter2:574GuavaCharStreams：589扫描仪读取器无下一测试：614扫描仪读数：633ApacheStringWriter：1544StreamApi：错误ParallelStreamApi：错误BufferReaderTest：错误InputStreamAndStringBuilder：错误
基准源代码
import com.google.common.io.CharStreams;
import org.apache.commons.io.IOUtils;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
/**
* Created by Ilya Gazman on 2/13/18.
*/
public class InputStreamToString {
private static final String UTF_8 = "UTF-8";
public static void main(String... args) {
log("App started");
byte[] bytes = new byte[1024 * 1024];
new Random().nextBytes(bytes);
log("Stream is ready\n");
try {
test(bytes);
} catch (IOException e) {
e.printStackTrace();
}
}
private static void test(byte[] bytes) throws IOException {
List<Stringify> tests = Arrays.asList(
new ApacheStringWriter(),
new ApacheStringWriter2(),
new NioStream(),
new ScannerReader(),
new ScannerReaderNoNextTest(),
new GuavaCharStreams(),
new StreamApi(),
new ParallelStreamApi(),
new ByteArrayOutputStreamTest(),
new BufferReaderTest(),
new BufferedInputStreamVsByteArrayOutputStream(),
new InputStreamAndStringBuilder(),
new Java9ISTransferTo(),
new Java9ISReadAllBytes()
);
String solution = new String(bytes, "UTF-8");
for (Stringify test : tests) {
try (ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes)) {
String s = test.inputStreamToString(inputStream);
if (!s.equals(solution)) {
log(test.name() + ": Error");
continue;
}
}
long startTime = System.currentTimeMillis();
for (int i = 0; i < 20; i++) {
try (ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes)) {
test.inputStreamToString(inputStream);
}
}
log(test.name() + ": " + (System.currentTimeMillis() - startTime));
}
}
private static void log(String message) {
System.out.println(message);
}
interface Stringify {
String inputStreamToString(InputStream inputStream) throws IOException;
default String name() {
return this.getClass().getSimpleName();
}
}
static class ApacheStringWriter implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
StringWriter writer = new StringWriter();
IOUtils.copy(inputStream, writer, UTF_8);
return writer.toString();
}
}
static class ApacheStringWriter2 implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
return IOUtils.toString(inputStream, UTF_8);
}
}
static class NioStream implements Stringify {
@Override
public String inputStreamToString(InputStream in) throws IOException {
ReadableByteChannel channel = Channels.newChannel(in);
ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 16);
ByteArrayOutputStream bout = new ByteArrayOutputStream();
WritableByteChannel outChannel = Channels.newChannel(bout);
while (channel.read(byteBuffer) > 0 || byteBuffer.position() > 0) {
byteBuffer.flip(); //make buffer ready for write
outChannel.write(byteBuffer);
byteBuffer.compact(); //make buffer ready for reading
}
channel.close();
outChannel.close();
return bout.toString(UTF_8);
}
}
static class ScannerReader implements Stringify {
@Override
public String inputStreamToString(InputStream is) throws IOException {
java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
return s.hasNext() ? s.next() : "";
}
}
static class ScannerReaderNoNextTest implements Stringify {
@Override
public String inputStreamToString(InputStream is) throws IOException {
java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
return s.next();
}
}
static class GuavaCharStreams implements Stringify {
@Override
public String inputStreamToString(InputStream is) throws IOException {
return CharStreams.toString(new InputStreamReader(
is, UTF_8));
}
}
static class StreamApi implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
return new BufferedReader(new InputStreamReader(inputStream))
.lines().collect(Collectors.joining("\n"));
}
}
static class ParallelStreamApi implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
return new BufferedReader(new InputStreamReader(inputStream)).lines()
.parallel().collect(Collectors.joining("\n"));
}
}
static class ByteArrayOutputStreamTest implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
try(ByteArrayOutputStream result = new ByteArrayOutputStream()) {
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) != -1) {
result.write(buffer, 0, length);
}
return result.toString(UTF_8);
}
}
}
static class BufferReaderTest implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
String newLine = System.getProperty("line.separator");
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder result = new StringBuilder(UTF_8);
String line;
boolean flag = false;
while ((line = reader.readLine()) != null) {
result.append(flag ? newLine : "").append(line);
flag = true;
}
return result.toString();
}
}
static class BufferedInputStreamVsByteArrayOutputStream implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
BufferedInputStream bis = new BufferedInputStream(inputStream);
ByteArrayOutputStream buf = new ByteArrayOutputStream();
int result = bis.read();
while (result != -1) {
buf.write((byte) result);
result = bis.read();
}
return buf.toString(UTF_8);
}
}
static class InputStreamAndStringBuilder implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
int ch;
StringBuilder sb = new StringBuilder(UTF_8);
while ((ch = inputStream.read()) != -1)
sb.append((char) ch);
return sb.toString();
}
}
static class Java9ISTransferTo implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
inputStream.transferTo(bos);
return bos.toString(UTF_8);
}
}
static class Java9ISReadAllBytes implements Stringify {
@Override
public String inputStreamToString(InputStream inputStream) throws IOException {
return new String(inputStream.readAllBytes(), UTF_8);
}
}
}
我做了一些计时测试，因为时间总是很重要的。
我试图以3种不同的方式将响应转换为字符串。（如下所示）为了可读性，我省略了try/catch块。
为了给出上下文，这是所有3种方法的前面代码：
String response;
String url = "www.blah.com/path?key=value";
GetMethod method = new GetMethod(url);
int status = client.executeMethod(method);
1)
response = method.getResponseBodyAsString();
2)
InputStream resp = method.getResponseBodyAsStream();
InputStreamReader is=new InputStreamReader(resp);
BufferedReader br=new BufferedReader(is);
String read = null;
StringBuffer sb = new StringBuffer();
while((read = br.readLine()) != null) {
sb.append(read);
}
response = sb.toString();
3)
InputStream iStream = method.getResponseBodyAsStream();
StringWriter writer = new StringWriter();
IOUtils.copy(iStream, writer, "UTF-8");
response = writer.toString();
因此，在使用相同的请求/响应数据对每种方法运行了500次测试之后，以下是数字。再次，这些是我的发现，你的发现可能不完全相同，但我写这篇文章是为了向其他人说明这些方法的效率差异。
排名：方法#1进近#3-比#1慢2.6%2号进近——比1号进近慢4.3%
任何这些方法都是获取响应并从中创建字符串的适当解决方案。
下面是如何仅使用JDK使用字节数组缓冲区来实现这一点。这实际上就是commons-ioIOUItils.copy（）方法的工作原理。如果要从Reader而不是InputStream复制，可以用char[]替换byte[]。
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
...
InputStream is = ....
ByteArrayOutputStream baos = new ByteArrayOutputStream(8192);
byte[] buffer = new byte[8192];
int count = 0;
try {
while ((count = is.read(buffer)) != -1) {
baos.write(buffer, 0, count);
}
}
finally {
try {
is.close();
}
catch (Exception ignore) {
}
}
String charset = "UTF-8";
String inputStreamAsString = baos.toString(charset);
此代码段位于\sdk\samples\android-19\connection\NetworkConnect\NetworkConnectSample\src\main\java.com\example\android\NetworkConnect\MainActivity.java中，该代码段根据Apache许可证2.0版授权，由Google编写。
/** Reads an InputStream and converts it to a String.
* @param stream InputStream containing HTML from targeted site.
* @param len Length of string that this method returns.
* @return String concatenated according to len parameter.
* @throws java.io.IOException
* @throws java.io.UnsupportedEncodingException
*/
private String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
一个很好的方法是使用Apache Commons IOUItils将InputStream复制到StringWriter中。。。类似于
StringWriter writer = new StringWriter();
IOUtils.copy(inputStream, writer, encoding);
String theString = writer.toString();
甚至
// NB: does not close inputStream, you'll have to use try-with-resources for that
String theString = IOUtils.toString(inputStream, encoding);
或者，如果不想混合流和写入器，可以使用ByteArrayOutputStream。
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