代表底層流的基本實體。通常是在http報文中獲取的實體。他只有一個空參的構造方法。

剛建立時沒有內容，長度為負值。需要通過兩個方法，把值賦進去。

、、、
/**
* BasicHttpEntity
* @throws IOException
*/
public static void testBasicHttpEntity() throws IOException{
InputStream is = null;
//BasicHttpEntity這類就是一個輸入流的內容包裝類，包裝內容的相關的編碼格式，長度等
BasicHttpEntity entity = new BasicHttpEntity();
//設定內容
entity.setContent(is);
//設定長度
entity.setContentLength(is.available());
//沒搞懂chunked這個屬性啥意思
entity.setChunked(false);
}

、、、

ByteArrayEntity

是自我包含的，可重複獲得使用的，從指定的位元組陣列中取出內容的實體。

位元組陣列是這個實體的構造方法的引數

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/**
* ByteArrayEntity
* @throws IOException
/
public static void testByteArrayEntity() throws IOException{
ByteArrayEntity entity = new ByteArrayEntity("內容".getBytes());
ByteArrayInputStream is = (ByteArrayInputStream) entity.getContent();
//上面這行程式碼返回的其實是一個ByteArrayInputStream物件
/

StringEntity

是自我包含的可重複的實體。通過String建立的實體

有兩個構造方法，一個是自Sring為引數的構造方法，一個是以String和字元編碼為引數的構造方法。

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/**
* StringEntity
* @throws IOException
*/
public static void testStringEntity() throws IOException{
StringBuilder sb = new StringBuilder();
//獲取系統的資訊集合，這個集合是不可以修改的
Map<String, String> nev = System.getenv();
for(Entry<String, String> entry : nev.entrySet()){
sb.append(entry.getKey()).append("=")
.append(entry.getValue()).append("\n");
}
String content = sb.toString();
System.out.println(content);
//建立只帶字串引數的
StringEntity entity = new StringEntity(content);
//建立帶字元創引數和字元編碼的
StringEntity entity2 = new StringEntity(content, "UTF-8");

}  

InputreamEntity

是流式不可以重複的實體。構造方法是InputStream 和內容長度，內容長度是輸入流的長度

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/**
* InputStreamEntity
* @throws IOException
*/
public static void testInputStreamEntity() throws IOException{
InputStream is = null;
//InputStreamEntity嚴格是對內容和長度相匹配的。用法和BasicHttpEntity類似
InputStreamEntity entity = new InputStreamEntity(is, is.available());
}

FileEntity

自我包含式，可以重複的實體。引數傳入檔案和檔案型別。

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/**
* FileEntity
* @throws IOException
*/
public static void testFileEntity() throws IOException{
FileEntity entity = new FileEntity(new File(""), ContentType.APPLICATION_FORM_URLENCODED);
FileEntity entity2 = new FileEntity(new File(""), "application/java-achive");

}  

EntityTemplete

從ContentProducer介面接受內容的實體。

在ContentProducer的實現類中寫入想要寫入的內容。

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/**
* EntityTemplate
* @throws IOException
*/
public static void testEntityTemplate() throws IOException{
ContentProducer producer = new ContentProducer() {

        @Override  
        public void writeTo(OutputStream outstream) throws IOException {  
            outstream.write("這是什麼東東》。".getBytes());  
        }  
    };  
      
    EntityTemplate entity = new EntityTemplate(producer);  
    entity.writeTo(System.out);  
}  

HttpEntityWrapper

這個是建立被包裝實體的基類，有被包裝實體的引用。

相當於實體的代理類，被包裝實體是他的一個屬性。

下面是這個類的原始碼：

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/*

• ====================================================================
• Licensed to the Apache Software Foundation (ASF) under one
• or more contributor license agreements. See the NOTICE file
• distributed with this work for additional information
• 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 except in compliance
• with the License. You may obtain a copy of the License at
• http://www.apache.org/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.
• ====================================================================
• This software consists of voluntary contributions made by many
• individuals on behalf of the Apache Software Foundation. For more
• information on the Apache Software Foundation, please see
• http://www.apache.org/.

*/

package org.apache.http.entity;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.annotation.NotThreadSafe;

/**

• Base class for wrapping entities.

• Keeps a {@link #wrappedEntity wrappedEntity} and delegates all

• calls to it. Implementations of wrapping entities can derive

• from this class and need to override only those methods that

• should not be delegated to the wrapped entity.

• @since 4.0
  */
  @NotThreadSafe
  public class HttpEntityWrapper implements HttpEntity {

  /** The wrapped entity. */
  protected HttpEntity wrappedEntity;

  /**

  • Creates a new entity wrapper.

  • @param wrapped the entity to wrap, not null

  • @throws IllegalArgumentException if wrapped is null
    */
    public HttpEntityWrapper(HttpEntity wrapped) {
    super();

    if (wrapped == null) {
    throw new IllegalArgumentException
    ("wrapped entity must not be null");
    }
    wrappedEntity = wrapped;

  } // constructor

  public boolean isRepeatable() {
  return wrappedEntity.isRepeatable();
  }

  public boolean isChunked() {
  return wrappedEntity.isChunked();
  }

  public long getContentLength() {
  return wrappedEntity.getContentLength();
  }

  public Header getContentType() {
  return wrappedEntity.getContentType();
  }

  public Header getContentEncoding() {
  return wrappedEntity.getContentEncoding();
  }

  public InputStream getContent()
  throws IOException {
  return wrappedEntity.getContent();
  }

  public void writeTo(OutputStream outstream)
  throws IOException {
  wrappedEntity.writeTo(outstream);
  }

  public boolean isStreaming() {
  return wrappedEntity.isStreaming();
  }

  /**

  • @deprecated (4.1) Either use {@link #getContent()} and call {@link java.io.InputStream#close()} on that;
  • otherwise call {@link #writeTo(OutputStream)} which is required to free the resources.
    */
    @Deprecated
    public void consumeContent() throws IOException {
    wrappedEntity.consumeContent();
    }

}

BufferedHttpEntity

是HttpEntityWarpper的子類，可以把不可以重複的實體，實現成可以重複的實體。

它從提供的實體中讀取內容，快取到內容中。

原始碼如下：

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/*

• ====================================================================
• Licensed to the Apache Software Foundation (ASF) under one
• or more contributor license agreements. See the NOTICE file
• distributed with this work for additional information
• 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 except in compliance
• with the License. You may obtain a copy of the License at
• http://www.apache.org/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.
• ====================================================================
• This software consists of voluntary contributions made by many
• individuals on behalf of the Apache Software Foundation. For more
• information on the Apache Software Foundation, please see
• http://www.apache.org/.

*/

package org.apache.http.entity;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.http.HttpEntity;
import org.apache.http.annotation.NotThreadSafe;
import org.apache.http.util.EntityUtils;

/**

• A wrapping entity that buffers it content if necessary.

• The buffered entity is always repeatable.

• If the wrapped entity is repeatable itself, calls are passed through.

• If the wrapped entity is not repeatable, the content is read into a

• buffer once and provided from there as often as required.

• @since 4.0
  */
  @NotThreadSafe
  public class BufferedHttpEntity extends HttpEntityWrapper {

  private final byte[] buffer;

  /**

  • Creates a new buffered entity wrapper.
  • @param entity the entity to wrap, not null
  • @throws IllegalArgumentException if wrapped is null
    */
    public BufferedHttpEntity(final HttpEntity entity) throws IOException {
    super(entity);
    if (!entity.isRepeatable() || entity.getContentLength() < 0) {
    this.buffer = EntityUtils.toByteArray(entity);
    } else {
    this.buffer = null;
    }
    }

  @Override
  public long getContentLength() {
  if (this.buffer != null) {
  return this.buffer.length;
  } else {
  return wrappedEntity.getContentLength();
  }
  }

  @Override
  public InputStream getContent() throws IOException {
  if (this.buffer != null) {
  return new ByteArrayInputStream(this.buffer);
  } else {
  return wrappedEntity.getContent();
  }
  }

  /**

  • Tells that this entity does not have to be chunked.
  • @return false
    */
    @Override
    public boolean isChunked() {
    return (buffer == null) && wrappedEntity.isChunked();
    }

  /**

  • Tells that this entity is repeatable.
  • @return true
    */
    @Override
    public boolean isRepeatable() {
    return true;
    }

  @Override
  public void writeTo(final OutputStream outstream) throws IOException {
  if (outstream == null) {
  throw new IllegalArgumentException("Output stream may not be null");
  }
  if (this.buffer != null) {
  outstream.write(this.buffer);
  } else {
  wrappedEntity.writeTo(outstream);
  }
  }

  // non-javadoc, see interface HttpEntity
  @Override
  public boolean isStreaming() {
  return (buffer == null) && wrappedEntity.isStreaming();
  }

} // class BufferedHttpEntity