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Java example source code file (ExceptionContext.java)

This example Java source code file (ExceptionContext.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, classnotfoundexception, exceptioncontext, hashmap, ioexception, locale, localizable, messageformat, object, serializable, set, string, stringbuilder, text, throwable, util

The ExceptionContext.java Java example source code

/*
 * 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.
 */
package org.apache.commons.math3.exception.util;

import java.util.List;
import java.util.ArrayList;
import java.util.Set;
import java.util.Map;
import java.io.IOException;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.util.HashMap;
import java.text.MessageFormat;
import java.util.Locale;

/**
 * Class that contains the actual implementation of the functionality mandated
 * by the {@link ExceptionContext} interface.
 * All Commons Math exceptions delegate the interface's methods to this class.
 *
 * @since 3.0
 */
public class ExceptionContext implements Serializable {
    /** Serializable version Id. */
    private static final long serialVersionUID = -6024911025449780478L;
    /**
     * The throwable to which this context refers to.
     */
    private Throwable throwable;
    /**
     * Various informations that enrich the informative message.
     */
    private List<Localizable> msgPatterns;
    /**
     * Various informations that enrich the informative message.
     * The arguments will replace the corresponding place-holders in
     * {@link #msgPatterns}.
     */
    private List<Object[]> msgArguments;
    /**
     * Arbitrary context information.
     */
    private Map<String, Object> context;

    /** Simple constructor.
     * @param throwable the exception this context refers too
     */
    public ExceptionContext(final Throwable throwable) {
        this.throwable = throwable;
        msgPatterns    = new ArrayList<Localizable>();
        msgArguments   = new ArrayList<Object[]>();
        context        = new HashMap<String, Object>();
    }

    /** Get a reference to the exception to which the context relates.
     * @return a reference to the exception to which the context relates
     */
    public Throwable getThrowable() {
        return throwable;
    }

    /**
     * Adds a message.
     *
     * @param pattern Message pattern.
     * @param arguments Values for replacing the placeholders in the message
     * pattern.
     */
    public void addMessage(Localizable pattern,
                           Object ... arguments) {
        msgPatterns.add(pattern);
        msgArguments.add(ArgUtils.flatten(arguments));
    }

    /**
     * Sets the context (key, value) pair.
     * Keys are assumed to be unique within an instance. If the same key is
     * assigned a new value, the previous one will be lost.
     *
     * @param key Context key (not null).
     * @param value Context value.
     */
    public void setValue(String key, Object value) {
        context.put(key, value);
    }

    /**
     * Gets the value associated to the given context key.
     *
     * @param key Context key.
     * @return the context value or {@code null} if the key does not exist.
     */
    public Object getValue(String key) {
        return context.get(key);
    }

    /**
     * Gets all the keys stored in the exception
     *
     * @return the set of keys.
     */
    public Set<String> getKeys() {
        return context.keySet();
    }

    /**
     * Gets the default message.
     *
     * @return the message.
     */
    public String getMessage() {
        return getMessage(Locale.US);
    }

    /**
     * Gets the message in the default locale.
     *
     * @return the localized message.
     */
    public String getLocalizedMessage() {
        return getMessage(Locale.getDefault());
    }

    /**
     * Gets the message in a specified locale.
     *
     * @param locale Locale in which the message should be translated.
     * @return the localized message.
     */
    public String getMessage(final Locale locale) {
        return buildMessage(locale, ": ");
    }

    /**
     * Gets the message in a specified locale.
     *
     * @param locale Locale in which the message should be translated.
     * @param separator Separator inserted between the message parts.
     * @return the localized message.
     */
    public String getMessage(final Locale locale,
                             final String separator) {
        return buildMessage(locale, separator);
    }

    /**
     * Builds a message string.
     *
     * @param locale Locale in which the message should be translated.
     * @param separator Message separator.
     * @return a localized message string.
     */
    private String buildMessage(Locale locale,
                                String separator) {
        final StringBuilder sb = new StringBuilder();
        int count = 0;
        final int len = msgPatterns.size();
        for (int i = 0; i < len; i++) {
            final Localizable pat = msgPatterns.get(i);
            final Object[] args = msgArguments.get(i);
            final MessageFormat fmt = new MessageFormat(pat.getLocalizedString(locale),
                                                        locale);
            sb.append(fmt.format(args));
            if (++count < len) {
                // Add a separator if there are other messages.
                sb.append(separator);
            }
        }

        return sb.toString();
    }

    /**
     * Serialize this object to the given stream.
     *
     * @param out Stream.
     * @throws IOException This should never happen.
     */
    private void writeObject(ObjectOutputStream out)
        throws IOException {
        out.writeObject(throwable);
        serializeMessages(out);
        serializeContext(out);
    }
    /**
     * Deserialize this object from the given stream.
     *
     * @param in Stream.
     * @throws IOException This should never happen.
     * @throws ClassNotFoundException This should never happen.
     */
    private void readObject(ObjectInputStream in)
        throws IOException,
               ClassNotFoundException {
        throwable = (Throwable) in.readObject();
        deSerializeMessages(in);
        deSerializeContext(in);
    }

    /**
     * Serialize  {@link #msgPatterns} and {@link #msgArguments}.
     *
     * @param out Stream.
     * @throws IOException This should never happen.
     */
    private void serializeMessages(ObjectOutputStream out)
        throws IOException {
        // Step 1.
        final int len = msgPatterns.size();
        out.writeInt(len);
        // Step 2.
        for (int i = 0; i < len; i++) {
            final Localizable pat = msgPatterns.get(i);
            // Step 3.
            out.writeObject(pat);
            final Object[] args = msgArguments.get(i);
            final int aLen = args.length;
            // Step 4.
            out.writeInt(aLen);
            for (int j = 0; j < aLen; j++) {
                if (args[j] instanceof Serializable) {
                    // Step 5a.
                    out.writeObject(args[j]);
                } else {
                    // Step 5b.
                    out.writeObject(nonSerializableReplacement(args[j]));
                }
            }
        }
    }

    /**
     * Deserialize {@link #msgPatterns} and {@link #msgArguments}.
     *
     * @param in Stream.
     * @throws IOException This should never happen.
     * @throws ClassNotFoundException This should never happen.
     */
    private void deSerializeMessages(ObjectInputStream in)
        throws IOException,
               ClassNotFoundException {
        // Step 1.
        final int len = in.readInt();
        msgPatterns = new ArrayList<Localizable>(len);
        msgArguments = new ArrayList<Object[]>(len);
        // Step 2.
        for (int i = 0; i < len; i++) {
            // Step 3.
            final Localizable pat = (Localizable) in.readObject();
            msgPatterns.add(pat);
            // Step 4.
            final int aLen = in.readInt();
            final Object[] args = new Object[aLen];
            for (int j = 0; j < aLen; j++) {
                // Step 5.
                args[j] = in.readObject();
            }
            msgArguments.add(args);
        }
    }

    /**
     * Serialize {@link #context}.
     *
     * @param out Stream.
     * @throws IOException This should never happen.
     */
    private void serializeContext(ObjectOutputStream out)
        throws IOException {
        // Step 1.
        final int len = context.size();
        out.writeInt(len);
        for (Map.Entry<String, Object> entry : context.entrySet()) {
            // Step 2.
            out.writeObject(entry.getKey());
            final Object value = entry.getValue();
            if (value instanceof Serializable) {
                // Step 3a.
                out.writeObject(value);
            } else {
                // Step 3b.
                out.writeObject(nonSerializableReplacement(value));
            }
        }
    }

    /**
     * Deserialize {@link #context}.
     *
     * @param in Stream.
     * @throws IOException This should never happen.
     * @throws ClassNotFoundException This should never happen.
     */
    private void deSerializeContext(ObjectInputStream in)
        throws IOException,
               ClassNotFoundException {
        // Step 1.
        final int len = in.readInt();
        context = new HashMap<String, Object>();
        for (int i = 0; i < len; i++) {
            // Step 2.
            final String key = (String) in.readObject();
            // Step 3.
            final Object value = in.readObject();
            context.put(key, value);
        }
    }

    /**
     * Replaces a non-serializable object with an error message string.
     *
     * @param obj Object that does not implement the {@code Serializable}
     * interface.
     * @return a string that mentions which class could not be serialized.
     */
    private String nonSerializableReplacement(Object obj) {
        return "[Object could not be serialized: " + obj.getClass().getName() + "]";
    }
}

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