Java tutorial
/* * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * 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 * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.script; import java.util.*; import java.io.*; /** * Simple implementation of ScriptContext. * * @author Mike Grogan * @since 1.6 */ public class SimpleScriptContext implements ScriptContext { /** * This is the writer to be used to output from scripts. * By default, a <code>PrintWriter</code> based on <code>System.out</code> * is used. Accessor methods getWriter, setWriter are used to manage * this field. * @see java.lang.System#out * @see java.io.PrintWriter */ protected Writer writer; /** * This is the writer to be used to output errors from scripts. * By default, a <code>PrintWriter</code> based on <code>System.err</code> is * used. Accessor methods getErrorWriter, setErrorWriter are used to manage * this field. * @see java.lang.System#err * @see java.io.PrintWriter */ protected Writer errorWriter; /** * This is the reader to be used for input from scripts. * By default, a <code>InputStreamReader</code> based on <code>System.in</code> * is used and default charset is used by this reader. Accessor methods * getReader, setReader are used to manage this field. * @see java.lang.System#in * @see java.io.InputStreamReader */ protected Reader reader; /** * This is the engine scope bindings. * By default, a <code>SimpleBindings</code> is used. Accessor * methods setBindings, getBindings are used to manage this field. * @see SimpleBindings */ protected Bindings engineScope; /** * This is the global scope bindings. * By default, a null value (which means no global scope) is used. Accessor * methods setBindings, getBindings are used to manage this field. */ protected Bindings globalScope; /** * Create a {@code SimpleScriptContext}. */ public SimpleScriptContext() { this(new InputStreamReader(System.in), new PrintWriter(System.out, true), new PrintWriter(System.err, true)); engineScope = new SimpleBindings(); globalScope = null; } /** * Package-private constructor to avoid needless creation of reader and writers. * It is the caller's responsability to initialize the engine scope. * * @param reader the reader * @param writer the writer * @param errorWriter the error writer */ SimpleScriptContext(Reader reader, Writer writer, Writer errorWriter) { this.reader = reader; this.writer = writer; this.errorWriter = errorWriter; } /** * Sets a <code>Bindings</code> of attributes for the given scope. If the value * of scope is <code>ENGINE_SCOPE</code> the given <code>Bindings</code> replaces the * <code>engineScope</code> field. If the value * of scope is <code>GLOBAL_SCOPE</code> the given <code>Bindings</code> replaces the * <code>globalScope</code> field. * * @param bindings The <code>Bindings</code> of attributes to set. * @param scope The value of the scope in which the attributes are set. * * @throws IllegalArgumentException if scope is invalid. * @throws NullPointerException if the value of scope is <code>ENGINE_SCOPE</code> and * the specified <code>Bindings</code> is null. */ public void setBindings(Bindings bindings, int scope) { switch (scope) { case ENGINE_SCOPE: if (bindings == null) { throw new NullPointerException("Engine scope cannot be null."); } engineScope = bindings; break; case GLOBAL_SCOPE: globalScope = bindings; break; default: throw new IllegalArgumentException("Invalid scope value."); } } /** * Retrieves the value of the attribute with the given name in * the scope occurring earliest in the search order. The order * is determined by the numeric value of the scope parameter (lowest * scope values first.) * * @param name The name of the attribute to retrieve. * @return The value of the attribute in the lowest scope for * which an attribute with the given name is defined. Returns * null if no attribute with the name exists in any scope. * @throws NullPointerException if the name is null. * @throws IllegalArgumentException if the name is empty. */ public Object getAttribute(String name) { checkName(name); if (engineScope.containsKey(name)) { return getAttribute(name, ENGINE_SCOPE); } else if (globalScope != null && globalScope.containsKey(name)) { return getAttribute(name, GLOBAL_SCOPE); } return null; } /** * Gets the value of an attribute in a given scope. * * @param name The name of the attribute to retrieve. * @param scope The scope in which to retrieve the attribute. * @return The value of the attribute. Returns <code>null</code> is the name * does not exist in the given scope. * * @throws IllegalArgumentException * if the name is empty or if the value of scope is invalid. * @throws NullPointerException if the name is null. */ public Object getAttribute(String name, int scope) { checkName(name); switch (scope) { case ENGINE_SCOPE: return engineScope.get(name); case GLOBAL_SCOPE: if (globalScope != null) { return globalScope.get(name); } return null; default: throw new IllegalArgumentException("Illegal scope value."); } } /** * Remove an attribute in a given scope. * * @param name The name of the attribute to remove * @param scope The scope in which to remove the attribute * * @return The removed value. * @throws IllegalArgumentException * if the name is empty or if the scope is invalid. * @throws NullPointerException if the name is null. */ public Object removeAttribute(String name, int scope) { checkName(name); switch (scope) { case ENGINE_SCOPE: if (getBindings(ENGINE_SCOPE) != null) { return getBindings(ENGINE_SCOPE).remove(name); } return null; case GLOBAL_SCOPE: if (getBindings(GLOBAL_SCOPE) != null) { return getBindings(GLOBAL_SCOPE).remove(name); } return null; default: throw new IllegalArgumentException("Illegal scope value."); } } /** * Sets the value of an attribute in a given scope. If the scope is <code>GLOBAL_SCOPE</code> * and no Bindings is set for <code>GLOBAL_SCOPE</code>, then setAttribute call is a no-op. * * @param name The name of the attribute to set * @param value The value of the attribute * @param scope The scope in which to set the attribute * * @throws IllegalArgumentException * if the name is empty or if the scope is invalid. * @throws NullPointerException if the name is null. */ public void setAttribute(String name, Object value, int scope) { checkName(name); switch (scope) { case ENGINE_SCOPE: engineScope.put(name, value); return; case GLOBAL_SCOPE: if (globalScope != null) { globalScope.put(name, value); } return; default: throw new IllegalArgumentException("Illegal scope value."); } } /** {@inheritDoc} */ public Writer getWriter() { return writer; } /** {@inheritDoc} */ public Reader getReader() { return reader; } /** {@inheritDoc} */ public void setReader(Reader reader) { this.reader = reader; } /** {@inheritDoc} */ public void setWriter(Writer writer) { this.writer = writer; } /** {@inheritDoc} */ public Writer getErrorWriter() { return errorWriter; } /** {@inheritDoc} */ public void setErrorWriter(Writer writer) { this.errorWriter = writer; } /** * Get the lowest scope in which an attribute is defined. * @param name Name of the attribute * . * @return The lowest scope. Returns -1 if no attribute with the given * name is defined in any scope. * @throws NullPointerException if name is null. * @throws IllegalArgumentException if name is empty. */ public int getAttributesScope(String name) { checkName(name); if (engineScope.containsKey(name)) { return ENGINE_SCOPE; } else if (globalScope != null && globalScope.containsKey(name)) { return GLOBAL_SCOPE; } else { return -1; } } /** * Returns the value of the <code>engineScope</code> field if specified scope is * <code>ENGINE_SCOPE</code>. Returns the value of the <code>globalScope</code> field if the specified scope is * <code>GLOBAL_SCOPE</code>. * * @param scope The specified scope * @return The value of either the <code>engineScope</code> or <code>globalScope</code> field. * @throws IllegalArgumentException if the value of scope is invalid. */ public Bindings getBindings(int scope) { if (scope == ENGINE_SCOPE) { return engineScope; } else if (scope == GLOBAL_SCOPE) { return globalScope; } else { throw new IllegalArgumentException("Illegal scope value."); } } /** {@inheritDoc} */ public List<Integer> getScopes() { return scopes; } private void checkName(String name) { Objects.requireNonNull(name); if (name.isEmpty()) { throw new IllegalArgumentException("name cannot be empty"); } } private static List<Integer> scopes; static { scopes = new ArrayList<Integer>(2); scopes.add(ENGINE_SCOPE); scopes.add(GLOBAL_SCOPE); scopes = Collections.unmodifiableList(scopes); } }