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最先，大家备考一下InputStream read方式的基本专业知识， java InputStream read方式內部有一个，postion，标示当今流载入到的部位，每载入一次，部位便会移动一次，假如读到最终，InputStream.read方式会回到-1，标示早已载入完后，假如想再度载入，能够启用inputstream.reset方式，position便会移动到之前启用mark的部位，mark默认设置是0，因此就可以从头开始再读过。 自然，可否reset是有标准的，它在于markSupported,markSupported() 方式回到是不是能够mark/reset 大家再回过头看request.getInputStream request.getInputStream回到的值是ServletInputStream,查询ServletInputStream源代码发觉，沒有重新写过reset方式，因此查询InputStream源代码发觉marksupported 回到false，而且reset方式，立即抛出去出现异常。 InputStream.java
public boolean markSupported() {
return false;
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
综上所述上述，在request.getinputstream载入一次后position来到文档结尾，第二次入读取不上数据信息，因为没法reset()，因此，request.getinputstream只有载入一次。 小结： 这一难题最压根還是对java IO的read、reset方式的深层次了解，特别是在是read方式的內部完成基本原理。 附ServletInputStream.java源代码
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work rmation regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file pliance with
* the License. You may obtain a copy of the License at
* licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
package javax.servlet;
import java.io.IOException;
import java.io.InputStream;
* Provides an input stream for reading binary data from a client request,
* including an efficient code readLine /code method for reading data one line
* at a time. With some protocols, such as HTTP POST and PUT, a
* code ServletInputStream /code object can be used to read data sent from the
* client.
* p
* A code ServletInputStream /code object is normally retrieved via the
* {@link ServletRequest#getInputStream} method.
* p
* This is an abstract class that a servlet container implements. Subclasses of
* this class must implement the code java.io.InputStream.read() /code method.
* @see ServletRequest
public abstract class ServletInputStream extends InputStream {
* Does nothing, because this is an abstract class.
protected ServletInputStream() {
// NOOP
* Reads the input stream, one line at a time. Starting at an offset, reads
* bytes into an array, until it reads a certain number of bytes or reaches
* a newline character, which it reads into the array as well.
* p
* This method returns -1 if it reaches the end of the input stream before
* reading the maximum number of bytes.
* @param b
* an array of bytes into which data is read
* @param off
* an integer specifying the character at which this method
* begins reading
* @param len
* an integer specifying the maximum number of bytes to read
* @return an integer specifying the actual number of bytes read, or -1 if
* the end of the stream is reached
* @exception IOException
* if an input or output exception has occurred
public int readLine(byte[] b, int off, int len) throws IOException {
if (len = 0) {
return 0;
int count = 0, c;
while ((c = read()) != -1) {
b[off++] = (byte) c;
count++;
if (c == '\n' || count == len) {
break;
return count 0 count : -1;
* Returns code true /code if all the data has been read from the stream,
* else code false /code .
* @since Servlet 3.1
public abstract boolean isFinished();
* Returns code true /code if data can be read without blocking, else
* code false /code . If this method is called and returns false, the
* container will invoke {@link ReadListener#onDataAvailable()} when data is
* available.
* @since Servlet 3.1
public abstract boolean isReady();
* Sets the {@link ReadListener} for this {@link ServletInputStream} and
* thereby switches to non-blocking IO. It is only valid to switch to
* non-blocking IO within async processing or HTTP upgrade processing.
* @param listener The non-blocking IO read listener
* @throws IllegalStateException If this method is called if neither
* async nor HTTP upgrade is in progress or
* if the {@link ReadListener} has already
* been set
* @throws NullPointerException If listener is null
* @since Servlet 3.1
public abstract void setReadListener(ReadListener listener);
之上这篇探讨request.getinputstream只有载入一次的难题便是网编共享给大伙儿的所有內容了，期待能给大伙儿一个参照，也期待大伙儿多多的适用。 |
