Java Precondition类
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Public final class Preconditions extends Object
通过Precondition类,你可以声明你期望为真的表达式,就像在JUnit assertTrue调用时的断言。
注意:在errorMessageTemplate参数中,只有”%s”会被当作占位符
通过这个类,可以优雅地完成参数检查工作。但是实话实说,如果仅仅因为这个类而引入guava jar包……
下面给出源码实现方法,可以自己在工程中简单实现自己所需功能。
/**
*Copyright (C) 2007 Google Inc.
*
*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.google.common.base;
importcom.google.common.annotations.GwtCompatible;
importcom.google.common.annotations.VisibleForTesting;
import java.util.Collection;
import java.util.NoSuchElementException;
/***
*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>
*
* tobe 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 withan
*<ahref="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"} specifieris 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 similartypes
* ofchecks! Precondition exceptions -- including those provided here, but also
*{@link IndexOutOfBoundsException}, {@link NoSuchElementException}, {@link
*UnsupportedOperationException} and others -- are used to signal that the
*<i>calling method</i> has made an error. This tells the caller thatit 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
*@since 2010.01.04 <b>stable</b> (imported from Google CollectionsLibrary)
*/
@GwtCompatible
public final class Preconditions {
private Preconditions() {}
/***
*Ensures the truth of an expression involving one or more parameters to the
*calling method.
*
*@param expression a boolean expression
*@throws IllegalArgumentException if {@code expression} is false
*/
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 stringusing {@link String#valueOf(Object)}
*@throws IllegalArgumentException if {@code expression} is false
*/
public static void checkArgument(boolean expression, ObjecterrorMessage) {
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 isformed by replacing each {@code %s}
* placeholder in the templatewith an argument. These are matched by
* position - the first {@code%s} gets {@code errorMessageArgs[0]}, etc.
* Unmatched arguments will beappended to the formatted message in square
* braces. Unmatchedplaceholders will be left as-is.
*@param errorMessageArgs the arguments to be substituted into the message
* template. Arguments areconverted to strings using
* {@linkString#valueOf(Object)}.
*@throws IllegalArgumentException if {@code expression} is false
*@throws NullPointerException if the check fails and either {@code
* errorMessageTemplate} or{@code errorMessageArgs} is null (don't let
* this happen)
*/
public static void checkArgument(boolean expression,
String errorMessageTemplate, Object... errorMessageArgs) {
if (!expression) {
throw new IllegalArgumentException(
format(errorMessageTemplate, errorMessageArgs));
}
}
/***
*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
*@throws IllegalStateException if {@code expression} is false
*/
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 stringusing {@link String#valueOf(Object)}
*@throws IllegalStateException if {@code expression} is false
*/
public static void checkState(boolean expression, 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 isformed by replacing each {@code %s}
* placeholder in the templatewith an argument. These are matched by
* position - the first {@code%s} gets {@code errorMessageArgs[0]}, etc.
* Unmatched arguments will beappended to the formatted message in square
* braces. Unmatchedplaceholders will be left as-is.
*@param errorMessageArgs the arguments to be substituted into the message
* template. Arguments areconverted to strings using
* {@linkString#valueOf(Object)}.
*@throws IllegalStateException if {@code expression} is false
*@throws NullPointerException if the check fails and either {@code
* errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
* this happen)
*/
public static void checkState(boolean expression,
String errorMessageTemplate, Object... errorMessageArgs) {
if (!expression) {
throw new IllegalStateException(
format(errorMessageTemplate, errorMessageArgs));
}
}
/***
*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
*@throws NullPointerException if {@code reference} is null
*/
public static <T> T checkNotNull(T reference) {
if (reference == null) {
throw new NullPointerException();
}
return reference;
}
/***
*Ensures that an object reference passed as a parameter to the calling
*method is not null.
*
*@param reference an object reference
*@param errorMessage the exception message to use if the check fails; will
* be converted to a string using {@linkString#valueOf(Object)}
*@return the non-null reference that was validated
*@throws NullPointerException if {@code reference} is null
*/
public static <T> T checkNotNull(T reference, Object errorMessage){
if (reference == null) {
throw new NullPointerException(String.valueOf(errorMessage));
}
return reference;
}
/***
*Ensures that an object reference passed as a parameter to the calling
*method is not null.
*
*@param reference an object reference
*@param errorMessageTemplate a template for the exception message should the
* check fail. The message isformed by replacing each {@code %s}
* placeholder in the templatewith an argument. These are matched by
* position - the first {@code%s} gets {@code errorMessageArgs[0]}, etc.
* Unmatched arguments will beappended to the formatted message in square
* braces. Unmatchedplaceholders will be left as-is.
*@param errorMessageArgs the arguments to be substituted into the message
* template. Arguments areconverted to strings using
* {@linkString#valueOf(Object)}.
*@return the non-null reference that was validated
*@throws NullPointerException if {@code reference} is null
*/
public static <T> T checkNotNull(T reference, StringerrorMessageTemplate,
Object... errorMessageArgs) {
if (reference == null) {
// If either of these parameters is null, the right thing happens anyway
throw new NullPointerException(
format(errorMessageTemplate, errorMessageArgs));
}
return reference;
}
/**
*All recent hotspots (as of 2009) *really* like to have the natural code
*
*if (guardExpression) {
* throw newBadException(messageExpression);
*}
*
*refactored so that messageExpression is moved to a separate
*String-returning method.
*
*if (guardExpression) {
* throw newBadException(badMsg(...));
*}
*
*The alternative natural refactorings into void or Exception-returning
*methods are much slower. This is a bigdeal - 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 theridiculous, 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 anarray,
*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}
*@throws IndexOutOfBoundsException if {@code index} is negative or is not
* less than {@code size}
*@throws IllegalArgumentException if {@code size} is negative
*/
public static int checkElementIndex(int index, int size) {
return checkElementIndex(index, size, "index");
}
/***
*Ensures that {@code index} specifies a valid <i>element</i> in anarray,
*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}
*@throws IndexOutOfBoundsException if {@code index} is negative or is not
* less than {@code size}
*@throws IllegalArgumentException if {@code size} is negative
*/
public static int checkElementIndex(int index, int size, String desc) {
// Carefully optimized for execution by hotspot (explanatory commentabove)
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
}
return index;
}
private static String badElementIndex(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 anarray,
*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}
*@throws IndexOutOfBoundsException if {@code index} is negative or is
* greater than {@code size}
*@throws IllegalArgumentException if {@code size} is negative
*/
public static int checkPositionIndex(int index, int size) {
return checkPositionIndex(index, size, "index");
}
/***
*Ensures that {@code index} specifies a valid <i>position</i> in anarray,
*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}
*@throws IndexOutOfBoundsException if {@code index} is negative or is
* greater than {@code size}
*@throws IllegalArgumentException if {@code size} is negative
*/
public static int checkPositionIndex(int index, int size, String desc) {
// Carefully optimized for execution by hotspot (explanatory commentabove)
if (index < 0 || index > size) {
throw new IndexOutOfBoundsException(badPositionIndex(index, size,desc));
}
return index;
}
private static String badPositionIndex(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
*@throws IndexOutOfBoundsException if either index is negative or is
* greater than {@code size},or if {@code end} is less than {@code start}
*@throws IllegalArgumentException if {@code size} is negative
*/
public static void checkPositionIndexes(int start, int end, int size) {
// Carefully optimized for execution by hotspot (explanatory commentabove)
if (start < 0 || end < start || end > size) {
throw new IndexOutOfBoundsException(badPositionIndexes(start, end,size));
}
}
private static String badPositionIndexes(int start, int end, int size) {
if (start < 0 || start > size) {
return badPositionIndex(start, size, "start index");
}
if (end < 0 || end > size) {
return badPositionIndex(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 areconverted to strings using
* {@linkString#valueOf(Object)}. Arguments can be null.
*/
@VisibleForTesting static String format(String template, Object... args){
// start substituting the arguments into the '%s' placeholders
StringBuilder builder = new StringBuilder(
template.length() + 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();
}
}
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