Java tutorial
/* * Licensed 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 com.iyonger.apm.web.util; import org.apache.commons.lang.StringUtils; import org.picocontainer.annotations.Nullable; import java.net.URL; /** * Simple static methods to be called at the start of your own methods to verify correct arguments and state. This * allows constructs such as * * <pre> * if (count <= 0) { * throw new IllegalArgumentException("must be positive: " + count); * } * </pre> * * to be replaced with the more compact * * <pre> * checkArgument(count > 0, "must be positive: %s", count); * </pre> * * Note that the sense of the expression is inverted; with {@code Preconditions} you declare what you expect to be * <i>true</i>, just as you do with an <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/assert.html"> * {@code assert}</a> or a JUnit {@code assertTrue} call. * * <p> * <b>Warning:</b> only the {@code "%s"} specifier is recognized as a placeholder in these messages, not the full range * of {@link String#format(String, Object[])} specifiers. * * <p> * Take care not to confuse precondition checking with other similar types of checks! Precondition exceptions -- * including those provided here, but also {@link IndexOutOfBoundsException}, {@link UnsupportedOperationException} and * others -- are used to signal that the <i>calling method</i> has made an error. This tells the caller that it should * not have invoked the method when it did, with the arguments it did, or perhaps ever. Postcondition or other * invariant * failures should not throw these types of exceptions. * * @author Kevin Bourrillion * @author JunHo Yoon (modify some.. add string related) * @since 2 (imported from Google Collections Library) */ @SuppressWarnings("UnusedDeclaration") public final class Preconditions { private static final int DEFAULT_16 = 16; private Preconditions() { } /** * Ensures the truth of an expression involving one or more parameters to the calling method. * * @param expression a boolean expression */ public static void checkArgument(boolean expression) { if (!expression) { throw new IllegalArgumentException(); } } /** * Ensures the truth of an expression involving one or more parameters to the calling method. * * @param expression a boolean expression * @param errorMessage the exception message to use if the check fails; will be converted to a string using * {@link String#valueOf(Object)} */ public static void checkArgument(boolean expression, @Nullable Object errorMessage) { if (!expression) { throw new IllegalArgumentException(String.valueOf(errorMessage)); } } /** * Ensures the truth of an expression involving one or more parameters to the calling method. * * @param expression a boolean expression * @param errorMessageTemplate a template for the exception message should the check fail. The message is formed by * replacing each * {@code %s} placeholder in the template with an argument. These are matched by position * - * the first * {@code %s} gets {@code errorMessageArgs[0]}, etc. Unmatched arguments will be appended * to the * formatted message in square braces. Unmatched placeholders will be left as-is. * @param errorMessageArgs the arguments to be substituted into the message template. Arguments are converted to * strings using * {@link String#valueOf(Object)}. */ public static void checkArgument(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) { if (!expression) { throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs)); } } /** * Ensures that an object reference passed as a parameter to the calling method is not null and also not empty. * * @param <T> type * @param expression array * @param errorMessageTemplate error message * @param errorMessageArgs args * @return the non-null reference and the non-empty value that was validated */ public static <T> T[] checkNotEmpty(T[] expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) { if (expression == null || expression.length == 0) { throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs)); } return expression; } /** * Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters * to the calling method. * * @param expression a boolean expression */ public static void checkState(boolean expression) { if (!expression) { throw new IllegalStateException(); } } /** * Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters * to the calling method. * * @param expression a boolean expression * @param errorMessage the exception message to use if the check fails; will be converted to a string using * {@link String#valueOf(Object)} */ public static void checkState(boolean expression, @Nullable Object errorMessage) { if (!expression) { throw new IllegalStateException(String.valueOf(errorMessage)); } } /** * Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters * to the calling method. * * @param expression a boolean expression * @param errorMessageTemplate a template for the exception message should the check fail. The message is formed by * replacing each * {@code %s} placeholder in the template with an argument. These are matched by position * - * the first * {@code %s} gets {@code errorMessageArgs[0]}, etc. Unmatched arguments will be appended * to the * formatted message in square braces. Unmatched placeholders will be left as-is. * @param errorMessageArgs the arguments to be substituted into the message template. Arguments are converted to * strings using * {@link String#valueOf(Object)}. */ public static void checkState(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) { if (!expression) { throw new IllegalStateException(format(errorMessageTemplate, errorMessageArgs)); } } // Added By JunHo Yoon /** * Ensures that an object reference passed as a parameter to the calling method is not null. * * @param reference an object reference * @return the non-null reference that was validated */ public static String checkNotEmpty(String reference) { if (StringUtils.isEmpty(reference)) { throw new IllegalArgumentException(); } return reference; } /** * Ensures that an object reference passed as a parameter to the calling method is not null. * * @param reference an object reference * @param errorMsg error message * @return the non-null reference that was validated */ public static String checkNotEmpty(String reference, String errorMsg) { if (StringUtils.isEmpty(reference)) { throw new IllegalArgumentException(errorMsg); } return reference; } /** * Ensures that an object reference passed as a parameter to the calling method is not 0. * * @param reference an object reference * @param errorMsg error message * @return the non-null reference that was validated */ public static Integer checkNotZero(Integer reference, String errorMsg) { if (reference == null || reference == 0) { throw new IllegalArgumentException(errorMsg); } return reference; } /** * Ensures that an object reference passed as a parameter to the calling method is not 0. * * @param reference an object reference * @param errorMsg error messgae. * @return the non-null reference that was validated */ public static Long checkNotZero(Long reference, String errorMsg) { if (reference == null || reference == 0L) { throw new IllegalArgumentException(errorMsg); } return reference; } /** * Ensures that an condition passed as a parameter is true. * * @param condition condition * @param errorMsg error message */ public static void checkTrue(boolean condition, String errorMsg) { if (!condition) { throw new IllegalArgumentException(errorMsg); } } /** * Ensures that an object reference passed as a parameter to the calling method is not null. * * @param <T> type * @param reference reference * @param message error message template * @param args error formatting element * @return the non-null reference that was validated */ public static <T> T checkExist(T reference, String message, Object... args) { if (reference == null) { throw new IllegalArgumentException(String.format(message, args)); } return reference; } /** * Ensures that the given reference is null. * * @param reference reference * @param errorMessageTemplate error message template * @param errorMessageArgs arguments to be filled in the template. */ public static <T> T checkNull(T reference, String errorMessageTemplate, Object... errorMessageArgs) { if (reference != null) { // If either of these parameters is null, the right thing happens anyway throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs)); } return reference; } /** * Ensures that an object reference passed as a parameter to the calling method is not null. * * @param <T> type * @param reference an object reference * @return the non-null reference that was validated */ public static <T> T checkNotNull(T reference) { if (reference == null) { throw new IllegalArgumentException(); } return reference; } /** * Ensures that an object reference passed as a parameter to the calling method is not null. * * @param <T> type * @param reference an object reference * @param errorMessage the exception message to use if the check fails; will be converted to a string using * {@link String#valueOf(Object)} * @return the non-null reference that was validated */ public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) { if (reference == null) { throw new IllegalArgumentException(String.valueOf(errorMessage)); } return reference; } /** * Ensures that an object reference passed as a parameter to the calling method is not null. * * @param <T> type * @param reference an object reference * @param errorMessageTemplate a template for the exception message should the check fail. The message is formed by * replacing each * {@code %s} placeholder in the template with an argument. These are matched by position * - * the first * {@code %s} gets {@code errorMessageArgs[0]}, etc. Unmatched arguments will be appended * to the * formatted message in square braces. Unmatched placeholders will be left as-is. * @param errorMessageArgs the arguments to be substituted into the message template. Arguments are converted to * strings using * {@link String#valueOf(Object)}. * @return the non-null reference that was validated */ public static <T> T checkNotNull(T reference, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) { if (reference == null) { // If either of these parameters is null, the right thing happens // anyway throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs)); } return reference; } /* * All recent hotspots (as of 2009) *really* like to have the natural code * * if (guardExpression) { throw new BadException(messageExpression); } * * refactored so that messageExpression is moved to a separate String-returning method. * * if (guardExpression) { throw new BadException(badMsg(...)); } * * The alternative natural refactorings into void or Exception-returning methods are much slower. This is a big deal * - we're talking factors of 2-8 in microbenchmarks, not just 10-20%. (This is a hotspot optimizer bug, which * should be fixed, but that's a separate, big project). * * The coding pattern above is heavily used in java.util, e.g. in ArrayList. There is a RangeCheckMicroBenchmark in * the JDK that was used to test this. * * But the methods in this class want to throw different exceptions, depending on the args, so it appears that this * pattern is not directly applicable. But we can use the ridiculous, devious trick of throwing an exception in the * middle of the construction of another exception. Hotspot is fine with that. */ /** * Ensures that {@code index} specifies a valid <i>element</i> in an array, list or string of size {@code size}. An * element index may range from zero, inclusive, to {@code size}, exclusive. * * @param index a user-supplied index identifying an element of an array, list or string * @param size the size of that array, list or string * @return the value of {@code index} */ public static int checkElementIndex(int index, int size) { return checkElementIndex(index, size, "index"); } /** * Ensures that {@code index} specifies a valid <i>element</i> in an array, list or string of size {@code size}. An * element index may range from zero, inclusive, to {@code size}, exclusive. * * @param index a user-supplied index identifying an element of an array, list or string * @param size the size of that array, list or string * @param desc the text to use to describe this index in an error message * @return the value of {@code index} */ public static int checkElementIndex(int index, int size, @Nullable String desc) { // Carefully optimized for execution by hotspot (explanatory comment // above) if (index < 0 || index >= size) { throw new IndexOutOfBoundsException(buildBadElementIndexMessage(index, size, desc)); } return index; } private static String buildBadElementIndexMessage(int index, int size, String desc) { if (index < 0) { return format("%s (%s) must not be negative", desc, index); } else if (size < 0) { throw new IllegalArgumentException("negative size: " + size); } else { // index >= size return format("%s (%s) must be less than size (%s)", desc, index, size); } } /** * Ensures that {@code index} specifies a valid <i>position</i> in an array, list or string of size {@code size}. A * position index may range from zero to {@code size}, inclusive. * * @param index a user-supplied index identifying a position in an array, list or string * @param size the size of that array, list or string * @return the value of {@code index} */ public static int checkPositionIndex(int index, int size) { return checkPositionIndex(index, size, "index"); } /** * Ensures that {@code index} specifies a valid <i>position</i> in an array, list or string of size {@code size}. A * position index may range from zero to {@code size}, inclusive. * * @param index a user-supplied index identifying a position in an array, list or string * @param size the size of that array, list or string * @param desc the text to use to describe this index in an error message * @return the value of {@code index} */ public static int checkPositionIndex(int index, int size, @Nullable String desc) { // Carefully optimized for execution by hotspot (explanatory comment // above) if (index < 0 || index > size) { throw new IndexOutOfBoundsException(buildBadPositionIndexMessage(index, size, desc)); } return index; } private static String buildBadPositionIndexMessage(int index, int size, String desc) { if (index < 0) { return format("%s (%s) must not be negative", desc, index); } else if (size < 0) { throw new IllegalArgumentException("negative size: " + size); } else { // index > size return format("%s (%s) must not be greater than size (%s)", desc, index, size); } } /** * Ensures that {@code start} and {@code end} specify a valid <i>positions</i> in an array, list or string of size * {@code size}, and are in order. A position index may range from zero to {@code size}, inclusive. * * @param start a user-supplied index identifying a starting position in an array, list or string * @param end a user-supplied index identifying a ending position in an array, list or string * @param size the size of that array, list or string */ public static void checkPositionIndexes(int start, int end, int size) { // Carefully optimized for execution by hotspot (explanatory comment // above) if (start < 0 || end < start || end > size) { throw new IndexOutOfBoundsException(buildBadPositionIndexesMessage(start, end, size)); } } private static String buildBadPositionIndexesMessage(int start, int end, int size) { if (start < 0 || start > size) { return buildBadPositionIndexMessage(start, size, "start index"); } if (end < 0 || end > size) { return buildBadPositionIndexMessage(end, size, "end index"); } // end < start return format("end index (%s) must not be less than start index (%s)", end, start); } /** * Substitutes each {@code %s} in {@code template} with an argument. These are matched by position - the first * {@code %s} gets {@code args[0]}, etc. If there are more arguments than placeholders, the unmatched arguments will * be appended to the end of the formatted message in square braces. * * @param template a non-null string containing 0 or more {@code %s} placeholders. * @param args the arguments to be substituted into the message template. Arguments are converted to strings using * {@link String#valueOf(Object)}. Arguments can be null. * @return formatted message */ static String format(String template, @Nullable Object... args) { template = String.valueOf(template); // null -> "null" // start substituting the arguments into the '%s' placeholders StringBuilder builder = new StringBuilder(template.length() + DEFAULT_16 * args.length); int templateStart = 0; int i = 0; while (i < args.length) { int placeholderStart = template.indexOf("%s", templateStart); if (placeholderStart == -1) { break; } builder.append(template.substring(templateStart, placeholderStart)); builder.append(args[i++]); templateStart = placeholderStart + 2; } builder.append(template.substring(templateStart)); // if we run out of placeholders, append the extra args in square braces if (i < args.length) { builder.append(" ["); builder.append(args[i++]); while (i < args.length) { builder.append(", "); builder.append(args[i++]); } builder.append(']'); } return builder.toString(); } /** * Ensures that given url is valid URL. * * @param url url String * @return converted url */ public static URL checkValidURL(String url) { try { return new URL(url); } catch (Exception e) { throw new IllegalArgumentException("Url " + url + "should be valid", e); } } }