Java实现Http服务器(二)

上节讲到的JDK自带的HttpServer组件，实现方法大概有三十个类构成，下面尝试着理解下实现思路。

由于Java的source代码中有很多注释，粘贴上来看着费劲，自己写个程序消除注释。

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 创建时间：2015-10-30 下午02:38:17 类说明 处理从JDK当中的注释
*/
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包下的类和接口提供了一系列的标准

sun.net.httpserver包下类根据标准做了一系列的实现

com.sun.net.httpserver.HttpServer.java

package com.sun.net.httpserver;

import com.sun.net.httpserver.spi.HttpServerProvider;

public abstract class HttpServer {

protected HttpServer () {
}

//默认创建HttpServer对象
public static HttpServer create () throws IOException {
return create (null, 0);
}

//根据InetSocketAddress对象和backlog对象创建HttpServer对象
public static HttpServer create (InetSocketAddress addr, int backlog) throws IOException
{
//HttpServer实例的服务提供者HttpServerProvider
HttpServerProvider provider = HttpServerProvider.provider();
//由服务提供者创建HttpServer对象
return provider.createHttpServer (addr, backlog);
}

//绑定网络地址接口
public abstract void bind (InetSocketAddress addr, int backlog) throws IOException;

//启动httpServer接口
public abstract void start () ;

//设置线程池
public abstract void setExecutor (Executor executor);

public abstract Executor getExecutor () ;

public abstract void stop (int delay);

//指定url和相应的处理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;
}
});
}
}

}

-----------------------分割线---------------------

上面说到com.sun.net.httpServer包下类和接口都是提供了一套标准，应用程序使用API的时候只关心这套标准，具体标准的实现应用程序是不关心的，实现了应用程序开发者和服务提供者的解耦，服务提供者可以提供多种多样的实现。



对于同一个功能，不同的厂家会提供不同的产品，比如不同品牌的轮胎、插头等。在软件行业，情况也是如此。比如，对于数据的加密解密，不同的厂家使用不同的算法，提供强度各异的不同软件包。应用软件根据不同的开发需求，往往需要使用不同的软件包。每次更换不同的软件包，都会重复以下过程：更改应用软件代码 -> 重新编译 -> 测试 -> 部署。这种做法一般被称为开发时绑定。这其实是一种比较原始的做法，缺乏灵活性和开放性。于是应用运行时绑定服务提供者的做法流行开来。具体做法是，使用配置文件指定，然后在运行时载入具体实现。Java SE 平台提供的 Service Provider 机制是折衷了开发时绑定和运行时绑定两种方式，很好的满足了高效和开放两个要求。

　　构成一个 Service Provider 框架需要大致三个部分，图 1 给出了一个典型的 Service Provider 组件结构。Java SE 平台的大部分 Service Provider 框架都提供了 3 个主要个组件：面向开发者的 Application 接口，面向服务提供商的 Service Provider 接口和真正的服务提供者。

---------------------------分割线------------------------

重点关注Application接口的两个方法

com.sun.net.httpServer.HttpServer.java

方法作用：

创建一个HttpServer实例，该实例绑定于一个确定的网络地址(由IP地址和端口号组成)
指定一个最大的监听backlog的长度，这个长度是指允许在这个监听Socket上排队等待连接的最大数量。

该HttpServer实例来自于当前的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);
}

这个模式和JAXP获取XML解析对象的过程很像

com.sun.net.httpServer.HttpServerProvider.java

方法作用：

针对JVM的请求返回系统的HttpServerProvider，查找过程

1：如果系统属性(system property) com.sun.net.httpserver.HttpServerProvider被定义过，找到相应的类

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包的属性文件当中是否有相应设置

查找所有加载的jar包中

META-INF/services

目录下的配置文件，文件名为

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下面的内部类

/**
* 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;
}
});
}
}

　　

最终如果前两种方法都没有找到相应的HttpServerProvider实例，则使用sun公司为我们提供的HttpServerProvider实例

sun.net.httpserver.DefaultHttpServerProvider类

也就是我们通常使用的类。

sun.net.httpserver.DefaultHttpServerProvider类

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类 （其实还有HTTPS的实现类，这里先不讲）

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();
}
}