上節講到的JDK自帶的HttpServer組件，實現方法大概有三十個類構成，下面嘗試着理解下實現思路。
由於Java的source代碼中有很多注釋，粘貼上來看着費勁，自己寫個程序消除注釋。
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
/**
* @author 作者 E-mail:
* @version 創建時間：2015-10-30 下午02:38:17 類說明 處理從JDK當中的注釋
*/
public class Test
{
public static void main(String[] args) throws IOException
{
FileInputStream inputStream = new FileInputStream("source");
FileOutputStream outputStream = new FileOutputStream("res");
BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
final StringBuilder builder = new StringBuilder();
String tempstr = null;
while ((tempstr = br.readLine()) != null)
{
if (tempstr.indexOf('*') == -1)
{
builder.append(tempstr + '\n');
}
}
outputStream.write(builder.toString().getBytes("gbk"));
}
}
com.sun.net.httpserver包下的類和接口提供了一系列的標准
sun.net.httpserver包下類根據標准做了一系列的實現
com.sun.net.httpserver.HttpServer.java
package com.sun.net.httpserver;
import com.sun.net.httpserver.spi.HttpServerProvider;
public abstract class HttpServer {
protected HttpServer () {
}
//默認創建HttpServer對象
public static HttpServer create () throws IOException {
return create (null, 0);
}
//根據InetSocketAddress對象和backlog對象創建HttpServer對象
public static HttpServer create (InetSocketAddress addr, int backlog) throws IOException
{
//HttpServer實例的服務提供者HttpServerProvider
HttpServerProvider provider = HttpServerProvider.provider();
//由服務提供者創建HttpServer對象
return provider.createHttpServer (addr, backlog);
}
//綁定網絡地址接口
public abstract void bind (InetSocketAddress addr, int backlog) throws IOException;
//啟動httpServer接口
public abstract void start () ;
//設置線程池
public abstract void setExecutor (Executor executor);
public abstract Executor getExecutor () ;
public abstract void stop (int delay);
//指定url和相應的處理Handler
public abstract HttpContext createContext (String path, HttpHandler handler) ;
public abstract HttpContext createContext (String path) ;
public abstract void removeContext (String path) throws IllegalArgumentException ;
public abstract void removeContext (HttpContext context) ;
public abstract InetSocketAddress getAddress() ;
}
com.sun.net.httpserver.spi.HttpServerProvider
package com.sun.net.httpserver.spi;
import java.io.FileDescriptor;
import java.io.IOException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import sun.misc.Service;
import sun.misc.ServiceConfigurationError;
import sun.security.action.GetPropertyAction;
public abstract class HttpServerProvider {
public abstract HttpServer createHttpServer (InetSocketAddress addr, int backlog) throws IOException;
public abstract HttpsServer createHttpsServer (InetSocketAddress addr, int backlog) throws IOException;
private static final Object lock = new Object();
private static HttpServerProvider provider = null;
protected HttpServerProvider() {
SecurityManager sm = System.getSecurityManager();
if (sm != null)
sm.checkPermission(new RuntimePermission("httpServerProvider"));
}
private static boolean loadProviderFromProperty() {
String cn = System.getProperty("com.sun.net.httpserver.HttpServerProvider");
if (cn == null)
return false;
try {
Class c = Class.forName(cn, true,
ClassLoader.getSystemClassLoader());
provider = (HttpServerProvider)c.newInstance();
return true;
} catch (ClassNotFoundException x) {
throw new ServiceConfigurationError(x);
} catch (IllegalAccessException x) {
throw new ServiceConfigurationError(x);
} catch (InstantiationException x) {
throw new ServiceConfigurationError(x);
} catch (SecurityException x) {
throw new ServiceConfigurationError(x);
}
}
private static boolean loadProviderAsService() {
Iterator i = Service.providers(HttpServerProvider.class,
ClassLoader.getSystemClassLoader());
for (;;) {
try {
if (!i.hasNext())
return false;
provider = (HttpServerProvider)i.next();
return true;
} catch (ServiceConfigurationError sce) {
if (sce.getCause() instanceof SecurityException) {
// Ignore the security exception, try the next provider
continue;
}
throw sce;
}
}
}
public static HttpServerProvider provider () {
synchronized (lock) {
if (provider != null)
return provider;
return (HttpServerProvider)AccessController
.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
if (loadProviderFromProperty())
return provider;
if (loadProviderAsService())
return provider;
provider = new sun.net.httpserver.DefaultHttpServerProvider();
return provider;
}
});
}
}
}
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上面說到com.sun.net.httpServer包下類和接口都是提供了一套標准，應用程序使用API的時候只關心這套標准，具體標准的實現應用程序是不關心的，實現了應用程序開發者和服務提供者的解耦，服務提供者可以提供多種多樣的實現。
對於同一個功能，不同的廠家會提供不同的產品，比如不同品牌的輪胎、插頭等。在軟件行業，情況也是如此。比如，對於數據的加密解密，不同的廠家使用不同的算法，提供強度各異的不同軟件包。應用軟件根據不同的開發需求，往往需要使用不同的軟件包。每次更換不同的軟件包，都會重復以下過程：更改應用軟件代碼 -> 重新編譯 -> 測試 -> 部署。這種做法一般被稱為開發時綁定。這其實是一種比較原始的做法，缺乏靈活性和開放性。於是應用運行時綁定服務提供者的做法流行開來。具體做法是，使用配置文件指定，然后在運行時載入具體實現。Java SE 平台提供的 Service Provider 機制是折衷了開發時綁定和運行時綁定兩種方式，很好的滿足了高效和開放兩個要求。
構成一個 Service Provider 框架需要大致三個部分，圖 1 給出了一個典型的 Service Provider 組件結構。Java SE 平台的大部分 Service Provider 框架都提供了 3 個主要個組件：面向開發者的 Application 接口，面向服務提供商的 Service Provider 接口和真正的服務提供者。
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重點關注Application接口的兩個方法
com.sun.net.httpServer.HttpServer.java
方法作用：
創建一個HttpServer實例，該實例綁定於一個確定的網絡地址(由IP地址和端口號組成)
指定一個最大的監聽backlog的長度，這個長度是指允許在這個監聽Socket上排隊等待連接的最大數量。
該HttpServer實例來自於當前的HttpServerProvider
/**
* Create a <code>HttpServer</code> instance which will bind to the
* specified {@link java.net.InetSocketAddress} (IP address and port number)
*
* A maximum backlog can also be specified. This is the maximum number of
* queued incoming connections to allow on the listening socket.
* Queued TCP connections exceeding this limit may be rejected by the TCP implementation.
* The HttpServer is acquired from the currently installed {@link HttpServerProvider}
*
* @param addr the address to listen on, if <code>null</code> then bind() must be called
* to set the address
* @param backlog the socket backlog. If this value is less than or equal to zero,
* then a system default value is used.
* @throws BindException if the server cannot bind to the requested address,
* or if the server is already bound.
* @throws IOException
*/
public static HttpServer create (
InetSocketAddress addr, int backlog
) throws IOException {
HttpServerProvider provider = HttpServerProvider.provider();
return provider.createHttpServer (addr, backlog);
}
這個模式和JAXP獲取XML解析對象的過程很像
com.sun.net.httpServer.HttpServerProvider.java
方法作用：
針對JVM的請求返回系統的HttpServerProvider，查找過程
1：如果系統屬性(system property) com.sun.net.httpserver.HttpServerProvider被定義過，找到相應的類
private static boolean loadProviderFromProperty() {
String cn = System.getProperty("com.sun.net.httpserver.HttpServerProvider");
if (cn == null)
return false;
try {
Class c = Class.forName(cn, true,
ClassLoader.getSystemClassLoader());
provider = (HttpServerProvider)c.newInstance();
return true;
} catch (ClassNotFoundException x) {
throw new ServiceConfigurationError(x);
} catch (IllegalAccessException x) {
throw new ServiceConfigurationError(x);
} catch (InstantiationException x) {
throw new ServiceConfigurationError(x);
} catch (SecurityException x) {
throw new ServiceConfigurationError(x);
}
}
2:第三方jar包的屬性文件當中是否有相應設置
查找所有加載的jar包中META-INF/services目錄下的配置文件，文件名為
private static boolean loadProviderAsService() {
Iterator i = Service.providers(HttpServerProvider.class,ClassLoader.getSystemClassLoader());
for (;;) {
try {
if (!i.hasNext())
return false;
provider = (HttpServerProvider)i.next();
return true;
} catch (ServiceConfigurationError sce) {
if (sce.getCause() instanceof SecurityException) {
// Ignore the security exception, try the next provider
continue;
}
throw sce;
}
}
}
sun.misc.Service.java
/**
* Locates and incrementally instantiates the available providers of a
* given service using the given class loader.
*
* <p> This method transforms the name of the given service class into a
* provider-configuration filename as described above and then uses the
* <tt>getResources</tt> method of the given class loader to find all
* available files with that name. These files are then read and parsed to
* produce a list of provider-class names. The iterator that is returned
* uses the given class loader to lookup and then instantiate each element
* of the list.
*
* <p> Because it is possible for extensions to be installed into a running
* Java virtual machine, this method may return different results each time
* it is invoked. <p>
*
* @param service
* The service's abstract service class
*
* @param loader
* The class loader to be used to load provider-configuration files
* and instantiate provider classes, or <tt>null</tt> if the system
* class loader (or, failing that the bootstrap class loader) is to
* be used
*
* @return An <tt>Iterator</tt> that yields provider objects for the given
* service, in some arbitrary order. The iterator will throw a
* <tt>ServiceConfigurationError</tt> if a provider-configuration
* file violates the specified format or if a provider class cannot
* be found and instantiated.
*
* @throws ServiceConfigurationError
* If a provider-configuration file violates the specified format
* or names a provider class that cannot be found and instantiated
*
* @see #providers(java.lang.Class)
* @see #installedProviders(java.lang.Class)
*/
public static Iterator providers(Class service, ClassLoader loader)
throws ServiceConfigurationError
{
return new LazyIterator(service, loader);
}
Service.java下面的內部類
/**
* Private inner class implementing fully-lazy provider lookup
*/
private static class LazyIterator implements Iterator {
Class service;
ClassLoader loader;
Enumeration configs = null;
Iterator pending = null;
Set returned = new TreeSet();
String nextName = null;
private LazyIterator(Class service, ClassLoader loader) {
this.service = service;
this.loader = loader;
}
public boolean hasNext() throws ServiceConfigurationError {
if (nextName != null) {
return true;
}
if (configs == null) {
try {
String fullName = prefix + service.getName();
if (loader == null)
configs = ClassLoader.getSystemResources(fullName);
else
configs = loader.getResources(fullName);
} catch (IOException x) {
fail(service, ": " + x);
}
}
while ((pending == null) || !pending.hasNext()) {
if (!configs.hasMoreElements()) {
return false;
}
pending = parse(service, (URL)configs.nextElement(), returned);
}
nextName = (String)pending.next();
return true;
}
public Object next() throws ServiceConfigurationError {
if (!hasNext()) {
throw new NoSuchElementException();
}
String cn = nextName;
nextName = null;
try {
return Class.forName(cn, true, loader).newInstance();
} catch (ClassNotFoundException x) {
fail(service,
"Provider " + cn + " not found");
} catch (Exception x) {
fail(service,
"Provider " + cn + " could not be instantiated: " + x,
x);
}
return null; /* This cannot happen */
}
public void remove() {
throw new UnsupportedOperationException();
}
}
/**
* Returns the system wide default HttpServerProvider for this invocation of
* the Java virtual machine.
*
* <p> The first invocation of this method locates the default provider
* object as follows: </p>
*
* <ol>
*
* <li><p> If the system property
* <tt>com.sun.net.httpserver.HttpServerProvider</tt> is defined then it is
* taken to be the fully-qualified name of a concrete provider class.
* The class is loaded and instantiated; if this process fails then an
* unspecified unchecked error or exception is thrown. </p></li>
*
* <li><p> If a provider class has been installed in a jar file that is
* visible to the system class loader, and that jar file contains a
* provider-configuration file named
* <tt>com.sun.net.httpserver.HttpServerProvider</tt> in the resource
* directory <tt>META-INF/services</tt>, then the first class name
* specified in that file is taken. The class is loaded and
* instantiated; if this process fails then an unspecified unchecked error or exception is
* thrown. </p></li>
*
* <li><p> Finally, if no provider has been specified by any of the above
* means then the system-default provider class is instantiated and the
* result is returned. </p></li>
*
* </ol>
*
* <p> Subsequent invocations of this method return the provider that was
* returned by the first invocation. </p>
*
* @return The system-wide default HttpServerProvider
*/
public static HttpServerProvider provider () {
synchronized (lock) {
if (provider != null)
return provider;
return (HttpServerProvider)AccessController
.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
if (loadProviderFromProperty())
return provider;
if (loadProviderAsService())
return provider;
provider = new sun.net.httpserver.DefaultHttpServerProvider();
return provider;
}
});
}
}
最終如果前兩種方法都沒有找到相應的HttpServerProvider實例，則使用sun公司為我們提供的HttpServerProvider實例
sun.net.httpserver.DefaultHttpServerProvider類
也就是我們通常使用的類。
sun.net.httpserver.DefaultHttpServerProvider類
package sun.net.httpserver;
import java.net.*;
import java.io.*;
import com.sun.net.httpserver.*;
import com.sun.net.httpserver.spi.*;
public class DefaultHttpServerProvider extends HttpServerProvider {
public HttpServer createHttpServer (InetSocketAddress addr, int backlog) throws IOException {
return new HttpServerImpl (addr, backlog);
}
public HttpsServer createHttpsServer (InetSocketAddress addr, int backlog) throws IOException {
return new HttpsServerImpl (addr, backlog);
}
}
sun.net.httpserver.HttpServerImpl類 （其實還有HTTPS的實現類，這里先不講）
package sun.net.httpserver;
import java.net.*;
import java.io.*;
import java.nio.*;
import java.security.*;
import java.nio.channels.*;
import java.util.*;
import java.util.concurrent.*;
import javax.net.ssl.*;
import com.sun.net.httpserver.*;
import com.sun.net.httpserver.spi.*;
public class HttpServerImpl extends HttpServer {
ServerImpl server;
HttpServerImpl () throws IOException {
this (new InetSocketAddress(80), 0);
}
HttpServerImpl (
InetSocketAddress addr, int backlog
) throws IOException {
server = new ServerImpl (this, "http", addr, backlog);
}
public void bind (InetSocketAddress addr, int backlog) throws IOException {
server.bind (addr, backlog);
}
public void start () {
server.start();
}
public void setExecutor (Executor executor) {
server.setExecutor(executor);
}
public Executor getExecutor () {
return server.getExecutor();
}
public void stop (int delay) {
server.stop (delay);
}
public HttpContextImpl createContext (String path, HttpHandler handler) {
return server.createContext (path, handler);
}
public HttpContextImpl createContext (String path) {
return server.createContext (path);
}
public void removeContext (String path) throws IllegalArgumentException {
server.removeContext (path);
}
public void removeContext (HttpContext context) throws IllegalArgumentException {
server.removeContext (context);
}
public InetSocketAddress getAddress() {
return server.getAddress();
}
}