URLStreamHandler.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.net;

import java.io.IOException;
import sun.net.util.IPAddressUtil;

/**
 * The abstract class {@code URLStreamHandler} is the common
 * superclass for all stream protocol handlers. A stream protocol
 * handler knows how to make a connection for a particular protocol
 * type, such as {@code http} or {@code https}.
 * <p>
 * In most cases, an instance of a {@code URLStreamHandler}
 * subclass is not created directly by an application. Rather, the
 * first time a protocol name is encountered when constructing a
 * {@code URL}, the appropriate stream protocol handler is
 * automatically loaded.
 *
 * @author James Gosling
 * @see java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)
 * @since 1.0
 */
// 流协议处理器的公共父类
public abstract class URLStreamHandler {
    
    /**
     * Opens a connection to the object referenced by the
     * {@code URL} argument.
     * This method should be overridden by a subclass.
     *
     * <p>If for the handler's protocol (such as HTTP or JAR), there
     * exists a public, specialized URLConnection subclass belonging
     * to one of the following packages or one of their subpackages:
     * java.lang, java.io, java.util, java.net, the connection
     * returned will be of that subclass. For example, for HTTP an
     * HttpURLConnection will be returned, and for JAR a
     * JarURLConnection will be returned.
     *
     * @param url the URL that this connects to.
     *
     * @return a {@code URLConnection} object for the {@code URL}.
     *
     * @throws IOException if an I/O error occurs while opening the
     *                     connection.
     */
    // 打开URL处的资源连接
    protected abstract URLConnection openConnection(URL url) throws IOException;
    
    /**
     * Same as openConnection(URL), except that the connection will be
     * made through the specified proxy; Protocol handlers that do not
     * support proxying will ignore the proxy parameter and make a
     * normal connection.
     *
     * Calling this method preempts the system's default
     * {@link java.net.ProxySelector ProxySelector} settings.
     *
     * @param url   the URL that this connects to.
     * @param proxy the proxy through which the connection will be made.
     *              If direct connection is desired, Proxy.NO_PROXY should be specified.
     *
     * @return a {@code URLConnection} object for the {@code URL}.
     *
     * @throws IOException                   if an I/O error occurs while opening the
     *                                       connection.
     * @throws IllegalArgumentException      if either u or p is null,
     *                                       or p has the wrong type.
     * @throws UnsupportedOperationException if the subclass that
     *                                       implements the protocol doesn't support this method.
     * @since 1.5
     */
    // 使用指定的代理打开URL处的资源连接
    protected URLConnection openConnection(URL url, java.net.Proxy proxy) throws IOException {
        throw new UnsupportedOperationException("Method not implemented.");
    }
    
    /**
     * Parses the string representation of a {@code URL} into a {@code URL} object.
     *
     * If there is any inherited context, then it has already been copied into the {@code URL} argument.
     * <p>
     * The {@code parseURL} method of {@code URLStreamHandler}
     * parses the string representation as if it were an
     * {@code http} specification. Most URL protocol families have a
     * similar parsing. A stream protocol handler for a protocol that has
     * a different syntax must override this routine.
     *
     * @param url   the {@code URL} to receive the result of parsing the spec.
     * @param spec  the {@code String} representing the URL that must be parsed.
     * @param start the character index at which to begin parsing.
     *              This is just past the '{@code :}' (if there is one) that specifies the determination of the protocol name.
     * @param limit the character position to stop parsing at.
     *              This is the end of the string or the position of the "{@code #}" character, if present.
     *              All information after the sharp sign indicates an anchor.
     */
    // 基于url解析spec中指定范围内的字符串，从spec中解析到的URL组件会覆盖到url中以形成新的URL返回，如果spec是相对路径，则会追加在url的原有路径上
    protected void parseURL(URL url, String spec, int start, int limit) {
        // These fields may receive context content if this was relative URL
        String protocol = url.getProtocol();
        String authority = url.getAuthority();
        String userInfo = url.getUserInfo();
        String host = url.getHost();
        int port = url.getPort();
        String path = url.getPath();
        String query = url.getQuery();
        // This field has already been parsed
        String ref = url.getRef();
        
        boolean isRelPath = false;
        boolean queryOnly = false;
        
        // FIX: should not assume query if opaque Strip off the query part
        if(start<limit) {
            // 获取查询串位置
            int queryStart = spec.indexOf('?');
            
            // 是否仅需要处理spec的查询串
            queryOnly = (queryStart == start);
            
            if((queryStart != -1) && (queryStart<limit)) {
                // 获取查询串后面的部分
                query = spec.substring(queryStart + 1, limit);
                
                // 获取查询串之前的部分
                spec = spec.substring(0, queryStart);
                
                limit = queryStart;
            }
        }
        
        int i = 0;
        
        // Parse the authority part if any
        boolean isUNCName = (start + 4<=limit) && (spec.charAt(start) == '/') && (spec.charAt(start + 1) == '/') && (spec.charAt(start + 2) == '/') && (spec.charAt(start + 3) == '/');
        
        if(!isUNCName && (start + 2<=limit) && (spec.charAt(start) == '/') && (spec.charAt(start + 1) == '/')) {
            start += 2;
            
            i = spec.indexOf('/', start);
            if(i<0 || i>limit) {
                i = spec.indexOf('?', start);
                if(i<0 || i>limit) {
                    i = limit;
                }
            }
            
            host = authority = spec.substring(start, i);
            
            int ind = authority.indexOf('@');
            if(ind != -1) {
                // 登录信息中只允许存在一个@
                if(ind != authority.lastIndexOf('@')) {
                    // more than one '@' in authority. This is not server based
                    userInfo = null;
                    host = null;
                } else {
                    // 获取用户信息
                    userInfo = authority.substring(0, ind);
                    host = authority.substring(ind + 1);
                }
            } else {
                userInfo = null;
            }
            
            // 从host中分离主机地址(主机名)和端口号
            if(host != null) {
                // If the host is surrounded by [ and ] then its an IPv6 literal address as specified in RFC2732
                if(host.length()>0 && (host.charAt(0) == '[')) {
                    if((ind = host.indexOf(']'))>2) {
                        String nhost = host;
                        host = nhost.substring(0, ind + 1);
                        if(!IPAddressUtil.isIPv6LiteralAddress(host.substring(1, ind))) {
                            throw new IllegalArgumentException("Invalid host: " + host);
                        }
                        
                        port = -1;
                        
                        if(nhost.length()>ind + 1) {
                            if(nhost.charAt(ind + 1) == ':') {
                                ++ind;
                                // port can be null according to RFC2396
                                if(nhost.length()>(ind + 1)) {
                                    port = Integer.parseInt(nhost, ind + 1, nhost.length(), 10);
                                }
                            } else {
                                throw new IllegalArgumentException("Invalid authority field: " + authority);
                            }
                        }
                    } else {
                        throw new IllegalArgumentException("Invalid authority field: " + authority);
                    }
                } else {
                    ind = host.indexOf(':');
                    port = -1;
                    if(ind >= 0) {
                        // port can be null according to RFC2396
                        if(host.length()>(ind + 1)) {
                            port = Integer.parseInt(host, ind + 1, host.length(), 10);
                        }
                        host = host.substring(0, ind);
                    }
                }
            } else {
                host = "";
            }
            
            if(port<-1) {
                throw new IllegalArgumentException("Invalid port number :" + port);
            }
            
            start = i;
            
            // If the authority is defined then the path is defined by the spec only; See RFC 2396 Section 5.2.4.
            if(authority != null && authority.length()>0) {
                path = "";
            }
        }
        
        if(host == null) {
            host = "";
        }
        
        // Parse the file path if any
        if(start<limit) {
            if(spec.charAt(start) == '/') {
                path = spec.substring(start, limit);
            } else if(path != null && path.length()>0) {
                isRelPath = true;
                int ind = path.lastIndexOf('/');
                String seperator = "";
                if(ind == -1 && authority != null) {
                    seperator = "/";
                }
                path = path.substring(0, ind + 1) + seperator + spec.substring(start, limit);
                
            } else {
                String seperator = (authority != null) ? "/" : "";
                path = seperator + spec.substring(start, limit);
            }
        } else if(queryOnly && path != null) {
            int ind = path.lastIndexOf('/');
            if(ind<0) {
                ind = 0;
            }
            path = path.substring(0, ind) + "/";
        }
        
        if(path == null) {
            path = "";
        }
        
        if(isRelPath) {
            // Remove embedded /./
            while((i = path.indexOf("/./")) >= 0) {
                path = path.substring(0, i) + path.substring(i + 2);
            }
            
            // Remove embedded /../ if possible
            i = 0;
            while((i = path.indexOf("/../", i)) >= 0) {
                /*
                 * A "/../" will cancel the previous segment and itself,
                 * unless that segment is a "/../" itself
                 * i.e. "/a/b/../c" becomes "/a/c"
                 * but "/../../a" should stay unchanged
                 */
                if(i>0 && (limit = path.lastIndexOf('/', i - 1)) >= 0 && (path.indexOf("/../", limit) != 0)) {
                    path = path.substring(0, limit) + path.substring(i + 3);
                    i = 0;
                } else {
                    i = i + 3;
                }
            }
            
            // Remove trailing .. if possible
            while(path.endsWith("/..")) {
                i = path.indexOf("/..");
                if((limit = path.lastIndexOf('/', i - 1)) >= 0) {
                    path = path.substring(0, limit + 1);
                } else {
                    break;
                }
            }
            
            // Remove starting .
            if(path.startsWith("./") && path.length()>2) {
                path = path.substring(2);
            }
            
            // Remove trailing .
            if(path.endsWith("/.")) {
                path = path.substring(0, path.length() - 1);
            }
        }
        
        setURL(url, protocol, host, port, authority, userInfo, path, query, ref);
    }
    
    /**
     * Returns the default port for a URL parsed by this handler. This method
     * is meant to be overidden by handlers with default port numbers.
     *
     * @return the default port for a {@code URL} parsed by this handler.
     *
     * @since 1.3
     */
    // 返回当前协议下的默认端口，有些协议需要端口支持
    protected int getDefaultPort() {
        return -1;
    }
    
    /**
     * Get the IP address of our host.
     * An empty host field or a DNS failure will result in a null return.
     *
     * @param url a URL object
     *
     * @return an {@code InetAddress} representing the host IP address.
     *
     * @since 1.3
     */
    // 返回指定url的主机地址
    protected synchronized InetAddress getHostAddress(URL url) {
        if(url.hostAddress != null) {
            return url.hostAddress;
        }
        
        String host = url.getHost();
        if(host == null || host.equals("")) {
            return null;
        }
        
        try {
            url.hostAddress = InetAddress.getByName(host);
        } catch(UnknownHostException ex) {
            return null;
        } catch(SecurityException se) {
            return null;
        }
        
        return url.hostAddress;
    }
    
    /**
     * Compares the host components of two URLs.
     *
     * @param url1 the URL of the first host to compare
     * @param url2 the URL of the second host to compare
     *
     * @return {@code true} if and only if they
     * are equal, {@code false} otherwise.
     *
     * @since 1.3
     */
    // 比较两个URL的host组件是否相同
    protected boolean hostsEqual(URL url1, URL url2) {
        InetAddress a1 = getHostAddress(url1);
        InetAddress a2 = getHostAddress(url2);
        
        // if we have internet address for both, compare them
        if(a1 != null && a2 != null) {
            return a1.equals(a2);
            // else, if both have host names, compare them
        } else if(url1.getHost() != null && url2.getHost() != null) {
            return url1.getHost().equalsIgnoreCase(url2.getHost());
        } else {
            return url1.getHost() == null && url2.getHost() == null;
        }
    }
    
    /**
     * Sets the fields of the {@code URL} argument to the indicated values.
     * Only classes derived from URLStreamHandler are able
     * to use this method to set the values of the URL fields.
     *
     * @param url       the URL to modify.
     * @param protocol  the protocol name.
     * @param host      the remote host value for the URL.
     * @param port      the port on the remote machine.
     * @param authority the authority part for the URL.
     * @param userInfo  the userInfo part of the URL.
     * @param path      the path component of the URL.
     * @param query     the query part for the URL.
     * @param ref       the reference.
     *
     * @throws SecurityException if the protocol handler of the URL is
     *                           different from this one
     * @since 1.3
     */
    // 为指定的url设置列出的组成部件
    protected void setURL(URL url, String protocol, String host, int port, String authority, String userInfo, String path, String query, String ref) {
        if(this != url.handler) {
            throw new SecurityException("handler for url different from " + "this handler");
        }
        
        // ensure that no one can reset the protocol on a given URL.
        url.set(url.getProtocol(), host, port, authority, userInfo, path, query, ref);
    }
    
    /**
     * Sets the fields of the {@code URL} argument to the indicated values.
     * Only classes derived from URLStreamHandler are able
     * to use this method to set the values of the URL fields.
     *
     * @param url      the URL to modify.
     * @param protocol the protocol name. This value is ignored since 1.2.
     * @param host     the remote host value for the URL.
     * @param port     the port on the remote machine.
     * @param file     the file.
     * @param ref      the reference.
     *
     * @throws SecurityException if the protocol handler of the URL is
     *                           different from this one
     * @deprecated Use setURL(URL, String, String, int, String, String, String, String);
     */
    @Deprecated
    protected void setURL(URL url, String protocol, String host, int port, String file, String ref) {
        /*
         * Only old URL handlers call this, so assume that the host
         * field might contain "user:passwd@host". Fix as necessary.
         */
        String authority = null;
        String userInfo = null;
        if(host != null && host.length() != 0) {
            authority = (port == -1) ? host : host + ":" + port;
            int at = host.lastIndexOf('@');
            if(at != -1) {
                userInfo = host.substring(0, at);
                host = host.substring(at + 1);
            }
        }
        
        /*
         * Assume file might contain query part. Fix as necessary.
         */
        String path = null;
        String query = null;
        if(file != null) {
            int q = file.lastIndexOf('?');
            if(q != -1) {
                query = file.substring(q + 1);
                path = file.substring(0, q);
            } else {
                path = file;
            }
        }
        
        setURL(url, protocol, host, port, authority, userInfo, path, query, ref);
    }
    
    /**
     * Compare two urls to see whether they refer to the same file,
     * i.e., having the same protocol, host, port, and path.
     * This method requires that none of its arguments is null. This is
     * guaranteed by the fact that it is only called indirectly
     * by java.net.URL class.
     *
     * @param url1 a URL object
     * @param ur2  a URL object
     *
     * @return true if url1 and ur2 refer to the same file
     *
     * @since 1.3
     */
    // 判断两个URL是否指向同一个资源
    protected boolean sameFile(URL url1, URL ur2) {
        // Compare the protocols.
        if(!((url1.getProtocol() == ur2.getProtocol()) || (url1.getProtocol() != null && url1.getProtocol().equalsIgnoreCase(ur2.getProtocol())))) {
            return false;
        }
        
        // Compare the files.
        if(!(url1.getFile() == ur2.getFile() || (url1.getFile() != null && url1.getFile().equals(ur2.getFile())))) {
            return false;
        }
        
        // Compare the ports.
        int port1, port2;
        port1 = (url1.getPort() != -1) ? url1.getPort() : url1.handler.getDefaultPort();
        port2 = (ur2.getPort() != -1) ? ur2.getPort() : ur2.handler.getDefaultPort();
        if(port1 != port2) {
            return false;
        }
        
        // Compare the hosts.
        return hostsEqual(url1, ur2);
    }
    
    /**
     * Converts a {@code URL} of a specific protocol to a
     * {@code String}.
     *
     * @param u the URL.
     *
     * @return a string representation of the {@code URL} argument.
     */
    protected String toExternalForm(URL u) {
        String s;
        return u.getProtocol() + ':' + (((s = u.getAuthority()) != null && s.length()>0) ? "//" + s : "") + (((s = u.getPath()) != null) ? s : "") + (((s = u.getQuery()) != null) ? '?' + s : "") + (((s = u.getRef()) != null) ? '#' + s : "");
    }
    
    
    /**
     * Provides the default equals calculation. May be overidden by handlers
     * for other protocols that have different requirements for equals().
     * This method requires that none of its arguments is null. This is
     * guaranteed by the fact that it is only called by java.net.URL class.
     *
     * @param url1 a URL object
     * @param ur2  a URL object
     *
     * @return {@code true} if the two urls are
     * considered equal, ie. they refer to the same
     * fragment in the same file.
     *
     * @since 1.3
     */
    protected boolean equals(URL url1, URL ur2) {
        String ref1 = url1.getRef();
        String ref2 = ur2.getRef();
        return (ref1 == ref2 || (ref1 != null && ref1.equals(ref2))) && sameFile(url1, ur2);
    }
    
    /**
     * Provides the default hash calculation. May be overidden by handlers for
     * other protocols that have different requirements for hashCode
     * calculation.
     *
     * @param u a URL object
     *
     * @return an {@code int} suitable for hash table indexing
     *
     * @since 1.3
     */
    protected int hashCode(URL u) {
        int h = 0;
        
        // Generate the protocol part.
        String protocol = u.getProtocol();
        if(protocol != null) {
            h += protocol.hashCode();
        }
        
        // Generate the host part.
        InetAddress addr = getHostAddress(u);
        if(addr != null) {
            h += addr.hashCode();
        } else {
            String host = u.getHost();
            if(host != null) {
                h += host.toLowerCase().hashCode();
            }
        }
        
        // Generate the file part.
        String file = u.getFile();
        if(file != null) {
            h += file.hashCode();
        }
        
        // Generate the port part.
        if(u.getPort() == -1) {
            h += getDefaultPort();
        } else {
            h += u.getPort();
        }
        
        // Generate the ref part.
        String ref = u.getRef();
        if(ref != null) {
            h += ref.hashCode();
        }
        
        return h;
    }
    
}