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) {
// ???
}
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
以下内容并没有回答最初的问题,而是回答了一些问题。
几个回答暗示了这种形式的循环
String line = null;
while((line = reader.readLine()) != null) {
// ...
}
or
for(String line = reader.readLine(); line != null; line = reader.readLine()) {
// ...
}
第一种形式通过在封闭作用域中声明一个变量“read”来污染封闭作用域的命名空间,该变量不会用于for循环之外的任何内容。第二个表单重复readline()调用。
这里有一种用Java编写这种循环的更简洁的方法。事实证明,for循环中的第一个子句不需要实际的初始值设定项值。这将变量“line”的范围保持在for循环的主体内。更优雅!我在任何地方都没有看到有人使用这个表单(几年前的一天我随机发现了它),但我一直在使用它。
for (String line; (line = reader.readLine()) != null; ) {
//...
}
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);
}
}
}
JDK中最简单的方法是使用以下代码片段。
String convertToString(InputStream in){
String resource = new Scanner(in).useDelimiter("\\Z").next();
return resource;
}
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。
String inputStreamToString(InputStream inputStream, Charset charset) throws IOException {
try (
final StringWriter writer = new StringWriter();
final InputStreamReader reader = new InputStreamReader(inputStream, charset)
) {
reader.transferTo(writer);
return writer.toString();
}
}
纯Java标准库解决方案-无库自Java 10以来-Reader#transferTo(Java.io.Writer)无环溶液无新行字符处理
Use:
InputStream in = /* Your InputStream */;
StringBuilder sb = new StringBuilder();
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String read;
while ((read=br.readLine()) != null) {
//System.out.println(read);
sb.append(read);
}
br.close();
return sb.toString();