HttpEntity的類型及其使用

1  BasicHttpEntity

      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。剛創建時沒有內容，長度爲負值。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();
  //設置內容
  entity.setContent(is);
  //設置長度
  entity.setContentLength(is.available());
  //沒搞懂chunked這個屬性啥意思
  entity.setChunked(false);
 }

2  ByteArrayEntity

    是自我包含的，可重複獲得使用的，從指定的字節數組中取出內容的實體。字節數組是這個實體的構造方法的參數。

/**
  * ByteArrayEntity
  * @throws IOException
  */
 public static void testByteArrayEntity() throws IOException{
  ByteArrayEntity entity = new ByteArrayEntity("內容".getBytes());
  ByteArrayInputStream is = (ByteArrayInputStream) entity.getContent();
  //上面這行代碼返回的其實是一個ByteArrayInputStream對象
  /*public InputStream getContent() {
         return new ByteArrayInputStream(this.b, this.off, this.len);
     }*/
 }

3  StringEntity

    是自我包含的可重複的實體。通過String創建的實體。有兩個構造方法，一個是自Sring爲參數的構造方法，一個是以String和字符編碼爲參數的構造方法。

/**
  * StringEntity
  * @throws IOException
  */
 public static void testStringEntity() throws IOException{
   StringBuilder sb = new StringBuilder();
   //獲取系統的信息集合，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);
   //創建只帶字符串參數的
   StringEntity entity = new StringEntity(content);
   //創建帶字符創參數和字符編碼的
   StringEntity entity2 = new StringEntity(content, "UTF-8");

 }

4  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。

/**
  * 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());
 }

5  FileEntity

    自我包含式，可以重複的實體。參數傳入文件和文件類型。

/**
  * 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

    從ContentProducer接口接受內容的實體。在ContentProducer的實現類中寫入想要寫入的內容。

/**
  * 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);
 }

7  HttpEntityWrapper

      這個是創建被包裝實體的基類，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。下面是這個類的源碼：

/*
 * ====================================================================
 * 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，緩存到內容中。源碼如下：

/*
 * ====================================================================
 * 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實體即可以使流也可以使字符串形式。具體有什麼用法看他的方法解釋：

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("這一個字符串實體", "UTF-8");
            //內容類型
            System.out.println(entity.getContentType());
            //內容的編碼格式
            System.out.println(entity.getContentEncoding());
            //內容的長度
            System.out.println(entity.getContentLength());
            //把內容轉成字符串
            System.out.println(EntityUtils.toString(entity));
            //內容轉成字節數組
            System.out.println(EntityUtils.toByteArray(entity).length);
            //還有個直接獲得流
            //entity.getContent();
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        } catch (ParseException e) {
        } catch (IOException e) {
        }

    }

}

2  對於實體的資源使用完之後要適當的回收資源，特別是對於流實體。例子代碼如下:

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{
                    //最後別忘了關閉應該關閉的資源，適當的釋放資源
                    if(is != null){
                        is.close();
                    }
                    //這個方法也可以把底層的流給關閉了
                    EntityUtils.consume(entity);
                    //下面是這方法的源碼
                    /*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();
                            }
                        }
                    }*/
                }

        }

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