一 HttpEntity的类型

1 BasicHttpEntity

代表底层流的基本实体。通常是在http报文中获取的实体。他只有一个空参的构造方法。刚创建时没有内容，长度为负值。需要通过两个方法，把值赋进去。

/**
* BasicHttpEntity
* @throws IOException
*/
public static void testBasicHttpEntity() throws IOException{
InputStream is = null;
//BasicHttpEntity这类就是一个输入流的内容包装类，包装内容的相关的编码格式，长度等
BasicHttpEntity entity = new BasicHttpEntity();
//设置内容
entity.setContent(is);
//设置长度
entity.setContentLength(is.available());
//没搞懂chunked这个属性啥意思
entity.setChunked(false);
}

2 ByteArrayEntity

是自我包含的，可重复获得使用的，从指定的字节数组中取出内容的实体。字节数组是这个实体的构造方法的参数。

/**
* ByteArrayEntity
* @throws IOException
*/
public static void testByteArrayEntity() throws IOException{
ByteArrayEntity entity = new ByteArrayEntity("内容".getBytes());
ByteArrayInputStream is = (ByteArrayInputStream) entity.getContent();
//上面这行代码返回的其实是一个ByteArrayInputStream对象
/*public InputStream getContent() {
return new ByteArrayInputStream(this.b, this.off, this.len);
}*/
}

3 StringEntity

是自我包含的可重复的实体。通过String创建的实体。有两个构造方法，一个是自Sring为参数的构造方法，一个是以String和字符编码为参数的构造方法。

/**
* StringEntity
* @throws IOException
*/
public static void testStringEntity() throws IOException{
StringBuilder sb = new StringBuilder();
//获取系统的信息集合，这个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);
//创建只带字符串参数的
StringEntity entity = new StringEntity(content);
//创建带字符创参数和字符编码的
StringEntity entity2 = new StringEntity(content, "UTF-8");
}

4 InputreamEntity

是流式不可以重复的实体。构造方法是InputStream 和内容长度，内容长度是输入流的长度。

/**
* InputStreamEntity
* @throws IOException
*/
public static void testInputStreamEntity() throws IOException{
InputStream is = null;
//InputStreamEntity严格是对内容和长度相匹配的。用法和BasicHttpEntity类似
InputStreamEntity entity = new InputStreamEntity(is, is.available());
}

5 FileEntity

自我包含式，可以重复的实体。参数传入文件和文件类型。

/**
* 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");
}

6 EntityTemplete

从ContentProducer接口接受内容的实体。在ContentProducer的实现类中写入想要写入的内容。

/**
* EntityTemplate
* @throws IOException
*/
public static void testEntityTemplate() throws IOException{
ContentProducer producer = new ContentProducer() {
@Override
public void writeTo(OutputStream outstream) throws IOException {
outstream.write("这是什么东东》。".getBytes());
}
};
EntityTemplate entity = new EntityTemplate(producer);
entity.writeTo(System.out);
}

7 HttpEntityWrapper

这个是创建被包装实体的基类，有被包装实体的引用。相当于实体的代理类，被包装实体是他的一个属性。下面是这个类的源码：

/*
* ====================================================================
* 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();
}
}

8 BufferedHttpEntity

是HttpEntityWarpper的子类，可以把不可以重复的实体，实现成可以重复的实体。它从提供的实体中读取内容，缓存到内容中。源码如下：

/*
* ====================================================================
* 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 <code>false</code>
*/
@Override
public boolean isChunked() {
return (buffer == null) && wrappedEntity.isChunked();
}
/**
* Tells that this entity is repeatable.
*
* @return <code>true</code>
*/
@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

二 HttpEntity 的使用

1 HttpEntity实体即可以使流也可以使字符串形式。具体有什么用法看他的方法解释：

package com.scl.base;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import org.apache.http.HttpEntity;
import org.apache.http.ParseException;
import org.apache.http.entity.StringEntity;
import org.apache.http.util.EntityUtils;
public class HttpClientDemo06 {
/**
* @param args
*/
public static void main(String[] args) {
try {
HttpEntity entity = new StringEntity("这一个字符串实体", "UTF-8");
//内容类型
System.out.println(entity.getContentType());
//内容的编码格式
System.out.println(entity.getContentEncoding());
//内容的长度
System.out.println(entity.getContentLength());
//把内容转成字符串
System.out.println(EntityUtils.toString(entity));
//内容转成字节数组
System.out.println(EntityUtils.toByteArray(entity).length);
//还有个直接获得流
//entity.getContent();
} catch (UnsupportedEncodingException e) {
throw new RuntimeException(e);
} catch (ParseException e) {
} catch (IOException e) {
}
}
}

2 对于实体的资源使用完之后要适当的回收资源，特别是对于流实体。例子代码如下:

public static void test() throws IllegalStateException, IOException{
HttpResponse response = null;
HttpEntity entity = response.getEntity();
if(entity!=null){
InputStream is = entity.getContent();
try{
//做一些操作
}finally{
//最后别忘了关闭应该关闭的资源，适当的释放资源
if(is != null){
is.close();
}
//这个方法也可以把底层的流给关闭了
EntityUtils.consume(entity);
//下面是这方法的源码
/*public static void consume(final HttpEntity entity) throws IOException {
if (entity == null) {
return;
}
if (entity.isStreaming()) {
InputStream instream = entity.getContent();
if (instream != null) {
instream.close();
}
}
}*/
}
}

FROM: http://blog.csdn.net/athenamax/article/details/8185043http://blog.csdn.net/athenamax/article/details/8185041

原文字体太小，看着眼睛疼，特此加大字体转载

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HttpEntity的类型及其使用