深入学习java源码之判断是否为空工具类
StringUtil的定义
字符串工具类，判断是否为空字符串(判断数据库有无数据null与“”)
public class StringUtil {
public static boolean isEmpty(String str) {
if (str == null || str.length() == 0) {
return true;
}
return false;
}
public static boolean isNotEmpty(String str) {
return !isEmpty(str);
}
}
isBlank()
判断某字符串是否为空或长度为0或由空白符(whitespace) 构成,对于制表符、换行符、换页符和回车符
StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false
-----------------------------------------
StringUtils.isBlank(null) = true
StringUtils.isBlank("") = true
StringUtils.isBlank(" ") = true
StringUtils.isBlank(" ") = true
StringUtils.isBlank("\t \n \f \r") = true
StringUtils.isBlank("\b") = false
StringUtils 判断某字符串是否为空
public class StringUtils {
/**
* Checks if a String is empty ("") or null.
*
*
* StringUtils.isEmpty(null) = true
* StringUtils.isEmpty("") = true
* StringUtils.isEmpty(" ") = false
* StringUtils.isEmpty("bob") = false
* StringUtils.isEmpty(" bob ") = false
*
*
* NOTE: This method changed in Lang version 2.0.
* It no longer trims the String.
* That functionality is available in isBlank().
*
* @param str the String to check, may be null
* @return true if the String is empty or null
*/
public static boolean isEmpty(String str) {
return (str == null || str.length() == 0);
}
/**
* Checks if a String is not empty ("") and not null.
*
*
* StringUtils.isNotEmpty(null) = false
* StringUtils.isNotEmpty("") = false
* StringUtils.isNotEmpty(" ") = true
* StringUtils.isNotEmpty("bob") = true
* StringUtils.isNotEmpty(" bob ") = true
*
*
* @param str the String to check, may be null
* @return true if the String is not empty and not null
*/
public static boolean isNotEmpty(String str) {
return (str != null && str.length() > 0);
}
/**
* Checks if a String is whitespace, empty ("") or null.
*
*
* StringUtils.isBlank(null) = true
* StringUtils.isBlank("") = true
* StringUtils.isBlank(" ") = true
* StringUtils.isBlank("bob") = false
* StringUtils.isBlank(" bob ") = false
*
*
* @param str the String to check, may be null
* @return true if the String is null, empty or whitespace
* @since 2.0
*/
public static boolean isBlank(String str) {
int strLen;
if (str == null || (strLen = str.length()) == 0) {
return true;
}
for (int i = 0; i < strLen; i++) {
if ((Character.isWhitespace(str.charAt(i)) == false) ) {
return false;
}
}
return true;
}
/**
* Checks if a String is not empty (""), not null and not whitespace only.
*
*
* StringUtils.isNotBlank(null) = false
* StringUtils.isNotBlank("") = false
* StringUtils.isNotBlank(" ") = false
* StringUtils.isNotBlank("bob") = true
* StringUtils.isNotBlank(" bob ") = true
*
*
* @param str the String to check, may be null
* @return true if the String is
* not empty and not null and not whitespace
* @since 2.0
*/
public static boolean isNotBlank(String str) {
int strLen;
if (str == null || (strLen = str.length()) == 0) {
return false;
}
for (int i = 0; i < strLen; i++) {
if ((Character.isWhitespace(str.charAt(i)) == false) ) {
return true;
}
}
return false;
}
public static boolean isWhitespace(String str) {
if (str == null) {
return false;
}
int sz = str.length();
for (int i = 0; i < sz; i++) {
if ((Character.isWhitespace(str.charAt(i)) == false) ) {
return false;
}
}
return true;
}
}
String类的定义
charAt() 方法用于返回指定索引处的字符。索引范围为从 0 到 length() - 1。
public final class String
implements java.io.Serializable, Comparable, CharSequence {
/** The value is used for character storage. */
private final char value[];
/** Cache the hash code for the string */
private int hash; // Default to 0
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -6849794470754667710L;
/**
* Class String is special cased within the Serialization Stream Protocol.
*
* A String instance is written into an ObjectOutputStream according to
*
* Object Serialization Specification, Section 6.2, "Stream Elements"
*/
private static final ObjectStreamField[] serialPersistentFields =
new ObjectStreamField[0];
/**
* Initializes a newly created {@code String} object so that it represents
* an empty character sequence. Note that use of this constructor is
* unnecessary since Strings are immutable.
*/
public String() {
this.value = "".value;
}
/**
* Initializes a newly created {@code String} object so that it represents
* the same sequence of characters as the argument; in other words, the
* newly created string is a copy of the argument string. Unless an
* explicit copy of {@code original} is needed, use of this constructor is
* unnecessary since Strings are immutable.
*
* @param original
* A {@code String}
*/
public String(String original) {
this.value = original.value;
this.hash = original.hash;
}
/**
* Allocates a new {@code String} so that it represents the sequence of
* characters currently contained in the character array argument. The
* contents of the character array are copied; subsequent modification of
* the character array does not affect the newly created string.
*
* @param value
* The initial value of the string
*/
public String(char value[]) {
this.value = Arrays.copyOf(value, value.length);
}
/**
* Returns the {@code char} value at the
* specified index. An index ranges from {@code 0} to
* {@code length() - 1}. The first {@code char} value of the sequence
* is at index {@code 0}, the next at index {@code 1},
* and so on, as for array indexing.
*
* If the {@code char} value specified by the index is a
* surrogate, the surrogate
* value is returned.
*
* @param index the index of the {@code char} value.
* @return the {@code char} value at the specified index of this string.
* The first {@code char} value is at index {@code 0}.
* @exception IndexOutOfBoundsException if the {@code index}
* argument is negative or not less than the length of this
* string.
*/
public char charAt(int index) {
if ((index < 0) || (index >= value.length)) {
throw new StringIndexOutOfBoundsException(index);
}
return value[index];
}
}
StringIndexOutOfBoundsException的定义
public
class StringIndexOutOfBoundsException extends IndexOutOfBoundsException {
private static final long serialVersionUID = -6762910422159637258L;
/**
* Constructs a {@code StringIndexOutOfBoundsException} with no
* detail message.
*
* @since JDK1.0.
*/
public StringIndexOutOfBoundsException() {
super();
}
/**
* Constructs a {@code StringIndexOutOfBoundsException} with
* the specified detail message.
*
* @param s the detail message.
*/
public StringIndexOutOfBoundsException(String s) {
super(s);
}
/**
* Constructs a new {@code StringIndexOutOfBoundsException}
* class with an argument indicating the illegal index.
*
* @param index the illegal index.
*/
public StringIndexOutOfBoundsException(int index) {
super("String index out of range: " + index);
}
ObjectUtils 对象判断是否为空工具类
package common;
import java.util.List;
import java.util.Map;
import com.google.common.collect.Maps;
/**
*
*/
public class ObjectUtils {
/**
*
* 方法描述 如果对象为非空返回true 否则返回false
*
* @param obj
* @return
*/
public static boolean isNotNull(Object obj) {
if(obj != null) {
return true;
}
return false;
}
/**
*
* 方法描述 如果对象为空返回 true 否则返回false
*
* @param obj
* @return
*/
public static boolean isNull(Object obj) {
if(obj != null) {
return false;
}
return true;
}
/**
*
* 方法描述 判断Map集合非null 非空 返回true 否则返回false
*
* @param list
* @return
*/
public static boolean isNotNull(Map map){
if(map != null && !map.isEmpty()) {
return true;
}
return false;
}
/**
*
* 方法描述 判断Map集合是null或者空 返回true 否则返回false
*
* @param list
* @return
*/
public static boolean isNull(Map map){
if(map == null || map.isEmpty()) {
return true;
}
return false;
}
/**
*
* 方法描述 判断Map集合非null 非空 返回true 否则返回false
*
* @param list
* @return
*/
public static boolean isNotNull(List list){
if(list != null && !list.isEmpty()) {
return true;
}
return false;
}
/**
*
* 方法描述 判断Map集合是null或者空 返回true 否则返回false
*
* @param list
* @return
*/
public static boolean isNull(List list){
if(list == null || list.isEmpty()) {
return true;
}
return false;
}
}
CollectionUtils 判断集合是否为空
public class CollectionUtils {
/**
* Checks if the specified collection/array/iterator is empty.
*
* This method can handles objects as follows
*
* - Collection - via collection isEmpty
*
- Map - via map isEmpty
*
- Array - using array size
*
- Iterator - via hasNext
*
- Enumeration - via hasMoreElements
*
*
* Note: This method is named to avoid clashing with
* {@link #isEmpty(Collection)}.
*
* @param object the object to get the size of, not null
* @return true if empty
* @throws IllegalArgumentException thrown if object is not recognised or null
* @since Commons Collections 3.2
*/
public static boolean sizeIsEmpty(Object object) {
if (object instanceof Collection) {
return ((Collection) object).isEmpty();
} else if (object instanceof Map) {
return ((Map) object).isEmpty();
} else if (object instanceof Object[]) {
return ((Object[]) object).length == 0;
} else if (object instanceof Iterator) {
return ((Iterator) object).hasNext() == false;
} else if (object instanceof Enumeration) {
return ((Enumeration) object).hasMoreElements() == false;
} else if (object == null) {
throw new IllegalArgumentException("Unsupported object type: null");
} else {
try {
return Array.getLength(object) == 0;
} catch (IllegalArgumentException ex) {
throw new IllegalArgumentException("Unsupported object type: " + object.getClass().getName());
}
}
}
//-----------------------------------------------------------------------
/**
* Null-safe check if the specified collection is empty.
*
* Null returns true.
*
* @param coll the collection to check, may be null
* @return true if empty or null
* @since Commons Collections 3.2
*/
public static boolean isEmpty(Collection coll) {
return (coll == null || coll.isEmpty());
}
/**
* Null-safe check if the specified collection is not empty.
*
* Null returns false.
*
* @param coll the collection to check, may be null
* @return true if non-null and non-empty
* @since Commons Collections 3.2
*/
public static boolean isNotEmpty(Collection coll) {
return !CollectionUtils.isEmpty(coll);
}
}
