commons-X系列

Posted 2020-11-04 寻渝记

 

1 commons-lang

　　1.1 ReflectionToStringBuilder

　　　　将对象进行字符串拼接

/*
 * 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.lang.builder;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.lang.ClassUtils;

/**
 * <p>
 * Assists in implementing {@link Object#toString()} methods using reflection.
 * </p>
 * 
 * <p>
 * This class uses reflection to determine the fields to append. Because these fields are usually private, the class
 * uses {@link java.lang.reflect.AccessibleObject#setAccessible(java.lang.reflect.AccessibleObject[], boolean)} to
 * change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions are
 * set up correctly.
 * </p>
 * 
 * <p>
 * A typical invocation for this method would look like:
 * </p>
 * 
 * <pre>
 * public String toString() {
 *   return ReflectionToStringBuilder.toString(this);
 * }</pre>
 * 
 * 
 * 
 * <p>
 * You can also use the builder to debug 3rd party objects:
 * </p>
 * 
 * <pre>
 * System.out.println("An object: " + ReflectionToStringBuilder.toString(anObject));</pre>
 * 
 * 
 * 
 * <p>
 * A subclass can control field output by overriding the methods:
 * <ul>
 * <li>{@link #accept(java.lang.reflect.Field)}</li>
 * <li>{@link #getValue(java.lang.reflect.Field)}</li>
 * </ul>
 * </p>
 * <p>
 * For example, this method does <i>not</i> include the <code>password</code> field in the returned
 * <code>String</code>:
 * </p>
 * 
 * <pre>
 * public String toString() {
 *     return (new ReflectionToStringBuilder(this) {
 *         protected boolean accept(Field f) {
 *             return super.accept(f) && !f.getName().equals("password");
 *         }
 *     }).toString();
 * }</pre>
 * 
 * 
 * 
 * <p>
 * The exact format of the <code>toString</code> is determined by the {@link ToStringStyle} passed into the
 * constructor.
 * </p>
 * 
 * @author Apache Software Foundation
 * @author Gary Gregory
 * @author Pete Gieser
 * @since 2.0
 * @version $Id: ReflectionToStringBuilder.java 905636 2010-02-02 14:03:32Z niallp $
 */
public class ReflectionToStringBuilder extends ToStringBuilder {

    /**
     * <p>
     * Builds a <code>toString</code> value using the default <code>ToStringStyle</code> through reflection.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     * 
     * <p>
     * Transient members will be not be included, as they are likely derived. Static fields will not be included.
     * Superclass fields will be appended.
     * </p>
     * 
     * @param object
     *            the Object to be output
     * @return the String result
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     */
    public static String toString(Object object) {
        return toString(object, null, false, false, null);
    }

    /**
     * <p>
     * Builds a <code>toString</code> value through reflection.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     * 
     * <p>
     * Transient members will be not be included, as they are likely derived. Static fields will not be included.
     * Superclass fields will be appended.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default <code>ToStringStyle</code> is used.
     * </p>
     * 
     * @param object
     *            the Object to be output
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @return the String result
     * @throws IllegalArgumentException
     *             if the Object or <code>ToStringStyle</code> is <code>null</code>
     */
    public static String toString(Object object, ToStringStyle style) {
        return toString(object, style, false, false, null);
    }

    /**
     * <p>
     * Builds a <code>toString</code> value through reflection.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     * 
     * <p>
     * If the <code>outputTransients</code> is <code>true</code>, transient members will be output, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the Object.
     * </p>
     * 
     * <p>
     * Static fields will not be included. Superclass fields will be appended.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default <code>ToStringStyle</code> is used.
     * </p>
     * 
     * @param object
     *            the Object to be output
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param outputTransients
     *            whether to include transient fields
     * @return the String result
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     */
    public static String toString(Object object, ToStringStyle style, boolean outputTransients) {
        return toString(object, style, outputTransients, false, null);
    }

    /**
     * <p>
     * Builds a <code>toString</code> value through reflection.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     * 
     * <p>
     * If the <code>outputTransients</code> is <code>true</code>, transient fields will be output, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the Object.
     * </p>
     * 
     * <p>
     * If the <code>outputStatics</code> is <code>true</code>, static fields will be output, otherwise they are
     * ignored.
     * </p>
     * 
     * <p>
     * Static fields will not be included. Superclass fields will be appended.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default <code>ToStringStyle</code> is used.
     * </p>
     * 
     * @param object
     *            the Object to be output
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param outputTransients
     *            whether to include transient fields
     * @param outputStatics
     *            whether to include transient fields
     * @return the String result
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @since 2.1
     */
    public static String toString(Object object, ToStringStyle style, boolean outputTransients, boolean outputStatics) {
        return toString(object, style, outputTransients, outputStatics, null);
    }

    /**
     * <p>
     * Builds a <code>toString</code> value through reflection.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     * 
     * <p>
     * If the <code>outputTransients</code> is <code>true</code>, transient fields will be output, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the Object.
     * </p>
     * 
     * <p>
     * If the <code>outputStatics</code> is <code>true</code>, static fields will be output, otherwise they are
     * ignored.
     * </p>
     * 
     * <p>
     * Superclass fields will be appended up to and including the specified superclass. A null superclass is treated as
     * <code>java.lang.Object</code>.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default <code>ToStringStyle</code> is used.
     * </p>
     * 
     * @param object
     *            the Object to be output
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param outputTransients
     *            whether to include transient fields
     * @param outputStatics
     *            whether to include static fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @return the String result
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @since 2.1
     */
    public static String toString(Object object, ToStringStyle style, boolean outputTransients, boolean outputStatics,
            Class reflectUpToClass) {
        return new ReflectionToStringBuilder(object, style, null, reflectUpToClass, outputTransients, outputStatics)
                .toString();
    }

    /**
     * <p>
     * Builds a <code>toString</code> value through reflection.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     * 
     * <p>
     * If the <code>outputTransients</code> is <code>true</code>, transient members will be output, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the Object.
     * </p>
     * 
     * <p>
     * Static fields will not be included. Superclass fields will be appended up to and including the specified
     * superclass. A null superclass is treated as <code>java.lang.Object</code>.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default <code>ToStringStyle</code> is used.
     * </p>
     * 
     * @deprecated Use {@link #toString(Object,ToStringStyle,boolean,boolean,Class)}
     * 
     * @param object
     *            the Object to be output
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param outputTransients
     *            whether to include transient fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @return the String result
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @since 2.0
     */
    public static String toString(Object object, ToStringStyle style, 
                                  boolean outputTransients, Class reflectUpToClass) 
    {
        return new ReflectionToStringBuilder(object, style, null, reflectUpToClass, outputTransients).toString();
    }

    /**
     * Builds a String for a toString method excluding the given field name.
     * 
     * @param object
     *            The object to "toString".
     * @param excludeFieldName
     *            The field name to exclude
     * @return The toString value.
     */
    public static String toStringExclude(Object object, final String excludeFieldName) {
        return toStringExclude(object, new String[]{excludeFieldName});
    }

    /**
     * Builds a String for a toString method excluding the given field names.
     * 
     * @param object
     *            The object to "toString".
     * @param excludeFieldNames
     *            The field names to exclude. Null excludes nothing.
     * @return The toString value.
     */
    public static String toStringExclude(Object object, Collection /*String*/ excludeFieldNames) {
        return toStringExclude(object, toNoNullStringArray(excludeFieldNames));
    }

    /**
     * Converts the given Collection into an array of Strings. The returned array does not contain <code>null</code>
     * entries. Note that {@link Arrays#sort(Object[])} will throw an {@link NullPointerException} if an array element 
     * is <code>null</code>.
     * 
     * @param collection
     *            The collection to convert
     * @return A new array of Strings.
     */
    static String[] toNoNullStringArray(Collection collection) {
        if (collection == null) {
            return ArrayUtils.EMPTY_STRING_ARRAY;
        }
        return toNoNullStringArray(collection.toArray());
    }

    /**
     * Returns a new array of Strings without null elements. Internal method used to normalize exclude lists
     * (arrays and collections). Note that {@link Arrays#sort(Object[])} will throw an {@link NullPointerException} 
     * if an array element is <code>null</code>.
     * 
     * @param array
     *            The array to check
     * @return The given array or a new array without null.
     */
    static String[] toNoNullStringArray(Object[] array) {
        ArrayList list = new ArrayList(array.length);
        for (int i = 0; i < array.length; i++) {
            Object e = array[i];
            if (e != null) {
                list.add(e.toString());
            }
        }
        return (String[]) list.toArray(ArrayUtils.EMPTY_STRING_ARRAY);
    }
    

    /**
     * Builds a String for a toString method excluding the given field names.
     * 
     * @param object
     *            The object to "toString".
     * @param excludeFieldNames
     *            The field names to exclude
     * @return The toString value.
     */
    public static String toStringExclude(Object object, String[] excludeFieldNames) {
        return new ReflectionToStringBuilder(object).setExcludeFieldNames(excludeFieldNames).toString();
    }

    /**
     * Whether or not to append static fields.
     */
    private boolean appendStatics = false;

    /**
     * Whether or not to append transient fields.
     */
    private boolean appendTransients = false;

    /**
     * Which field names to exclude from output. Intended for fields like <code>"password"</code>.
     */
    private String[] excludeFieldNames;

    /**
     * The last super class to stop appending fields for.
     */
    private Class upToClass = null;

    /**
     * <p>
     * Constructor.
     * </p>
     * 
     * <p>
     * This constructor outputs using the default style set with <code>setDefaultStyle</code>.
     * </p>
     * 
     * @param object
     *            the Object to build a <code>toString</code> for, must not be <code>null</code>
     * @throws IllegalArgumentException
     *             if the Object passed in is <code>null</code>
     */
    public ReflectionToStringBuilder(Object object) {
        super(object);
    }

    /**
     * <p>
     * Constructor.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default style is used.
     * </p>
     * 
     * @param object
     *            the Object to build a <code>toString</code> for, must not be <code>null</code>
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @throws IllegalArgumentException
     *             if the Object passed in is <code>null</code>
     */
    public ReflectionToStringBuilder(Object object, ToStringStyle style) {
        super(object, style);
    }

    /**
     * <p>
     * Constructor.
     * </p>
     * 
     * <p>
     * If the style is <code>null</code>, the default style is used.
     * </p>
     * 
     * <p>
     * If the buffer is <code>null</code>, a new one is created.
     * </p>
     * 
     * @param object
     *            the Object to build a <code>toString</code> for
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param buffer
     *            the <code>StringBuffer</code> to populate, may be <code>null</code>
     * @throws IllegalArgumentException
     *             if the Object passed in is <code>null</code>
     */
    public ReflectionToStringBuilder(Object object, ToStringStyle style, StringBuffer buffer) {
        super(object, style, buffer);
    }

    /**
     * Constructor.
     * 
     * @deprecated Use {@link #ReflectionToStringBuilder(Object,ToStringStyle,StringBuffer,Class,boolean,boolean)}.
     * 
     * @param object
     *            the Object to build a <code>toString</code> for
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param buffer
     *            the <code>StringBuffer</code> to populate, may be <code>null</code>
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @param outputTransients
     *            whether to include transient fields
     */
    public ReflectionToStringBuilder(Object object, ToStringStyle style, StringBuffer buffer, Class reflectUpToClass,
            boolean outputTransients) {
        super(object, style, buffer);
        this.setUpToClass(reflectUpToClass);
        this.setAppendTransients(outputTransients);
    }

    /**
     * Constructor.
     * 
     * @param object
     *            the Object to build a <code>toString</code> for
     * @param style
     *            the style of the <code>toString</code> to create, may be <code>null</code>
     * @param buffer
     *            the <code>StringBuffer</code> to populate, may be <code>null</code>
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @param outputTransients
     *            whether to include transient fields
     * @param outputStatics
     *            whether to include static fields
     * @since 2.1
     */
    public ReflectionToStringBuilder(Object object, ToStringStyle style, StringBuffer buffer, Class reflectUpToClass,
            boolean outputTransients, boolean outputStatics) {
        super(object, style, buffer);
        this.setUpToClass(reflectUpToClass);
        this.setAppendTransients(outputTransients);
        this.setAppendStatics(outputStatics);
    }

    /**
     * Returns whether or not to append the given <code>Field</code>.
     * <ul>
     * <li>Transient fields are appended only if {@link #isAppendTransients()} returns <code>true</code>.
     * <li>Static fields are appended only if {@link #isAppendStatics()} returns <code>true</code>.
     * <li>Inner class fields are not appened.</li>
     * </ul>
     * 
     * @param field
     *            The Field to test.
     * @return Whether or not to append the given <code>Field</code>.
     */
    protected boolean accept(Field field) {
        if (field.getName().indexOf(ClassUtils.INNER_CLASS_SEPARATOR_CHAR) != -1) {
            // Reject field from inner class.
            return false;
        }
        if (Modifier.isTransient(field.getModifiers()) && !this.isAppendTransients()) {
            // Reject transient fields.
            return false;
        }
        if (Modifier.isStatic(field.getModifiers()) && !this.isAppendStatics()) {
            // Reject static fields.
            return false;
        }
        if (this.getExcludeFieldNames() != null
            && Arrays.binarySearch(this.getExcludeFieldNames(), field.getName()) >= 0) {
            // Reject fields from the getExcludeFieldNames list.
            return false;
        }
        return true;
    }

    /**
     * <p>
     * Appends the fields and values defined by the given object of the given Class.
     * </p>
     * 
     * <p>
     * If a cycle is detected as an object is &quot;toString()\'ed&quot;, such an object is rendered as if
     * <code>Object.toString()</code> had been called and not implemented by the object.
     * </p>
     * 
     * @param clazz
     *            The class of object parameter
     */
    protected void appendFieldsIn(Class clazz) {
        if (clazz.isArray()) {
            this.reflectionAppendArray(this.getObject());
            return;
        }
        Field[] fields = clazz.getDeclaredFields();
        AccessibleObject.setAccessible(fields, true);
        for (int i = 0; i < fields.length; i++) {
            Field field = fields[i];
            String fieldName = field.getName();
            if (this.accept(field)) {
                try {
                    // Warning: Field.get(Object) creates wrappers objects
                    // for primitive types.
                    Object fieldValue = this.getValue(field);
                    this.append(fieldName, fieldValue);
                } catch (IllegalAccessException ex) {
                    //this can\'t happen. Would get a Security exception
                    // instead
                    //throw a runtime exception in case the impossible
                    // happens.
                    throw new InternalError("Unexpected IllegalAccessException: " + ex.getMessage());
                }
            }
        }
    }

    /**
     * @return Returns the excludeFieldNames.
     */
    public String[] getExcludeFieldNames() {
        return this.excludeFieldNames;
    }

    /**
     * <p>
     * Gets the last super class to stop appending fields for.
     * </p>
     * 
     * @return The last super class to stop appending fields for.
     */
    public Class getUpToClass() {
        return this.upToClass;
    }

    /**
     * <p>
     * Calls <code>java.lang.reflect.Field.get(Object)</code>.
     * </p>
     * 
     * @param field
     *            The Field to query.
     * @return The Object from the given Field.
     * 
     * @throws IllegalArgumentException
     *             see {@link java.lang.reflect.Field#get(Object)}
     * @throws IllegalAccessException
     *             see {@link java.lang.reflect.Field#get(Object)}
     * 
     * @see java.lang.reflect.Field#get(Object)
     */
    protected Object getValue(Field field) throws IllegalArgumentException, IllegalAccessException {
        return field.get(this.getObject());
    }

    /**
     * <p>
     * Gets whether or not to append static fields.
     * </p>
     * 
     * @return Whether or not to append static fields.
     * @since 2.1
     */
    public boolean isAppendStatics() {
        return this.appendStatics;
    }

    /**
     * <p>
     * Gets whether or not to append transient fields.
     * </p>
     * 
     * @return Whether or not to append transient fields.
     */
    public boolean isAppendTransients() {
        return this.appendTransients;
    }

    /**
     * <p>
     * Append to the <code>toString</code> an <code>Object</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>toString</code>
     * @return this
     */
    public ToStringBuilder reflectionAppendArray(Object array) {
        this.getStyle().reflectionAppendArrayDetail(this.getStringBuffer(), null, array);
        return this;
    }

    /**
     * <p>
     * Sets whether or not to append static fields.
     * </p>
     * 
     * @param appendStatics
     *            Whether or not to append static fields.
     * @since 2.1
     */
    public void setAppendStatics(boolean appendStatics) {
        this.appendStatics = appendStatics;
    }

    /**
     * <p>
     * Sets whether or not to append transient fields.
     * </p>
     * 
     * @param appendTransients
     *            Whether or not to append transient fields.
     */
    public void setAppendTransients(boolean appendTransients) {
        this.appendTransients = appendTransients;
    }

    /**
     * Sets the field names to exclude.
     * 
     * @param excludeFieldNamesParam
     *            The excludeFieldNames to excluding from toString or <code>null</code>.
     * @return <code>this</code>
     */
    public ReflectionToStringBuilder setExcludeFieldNames(String[] excludeFieldNamesParam) {
        if (excludeFieldNamesParam == null) {
            this.excludeFieldNames = null;
        } else {
            this.excludeFieldNames = toNoNullStringArray(excludeFieldNamesParam);
            Arrays.sort(this.excludeFieldNames);
        }
        return this;
    }

    /**
     * <p>
     * Sets the last super class to stop appending fields for.
     * </p>
     * 
     * @param clazz
     *            The last super class to stop appending fields for.
     */
    public void setUpToClass(Class clazz) {
        if (clazz != null) {
            Object object = getObject();
            if (object != null && clazz.isInstance(object) == false) {
                throw new IllegalArgumentException("Specified class is not a superclass of the object");
            }
        }
        this.upToClass = clazz;
    }

    /**
     * <p>
     * Gets the String built by this builder.
     * </p>
     * 
     * @return the built string
     */
    public String toString() {
        if (this.getObject() == null) {
            return this.getStyle().getNullText();
        }
        Class clazz = this.getObject().getClass();
        this.appendFieldsIn(clazz);
        while (clazz.getSuperclass() != null && clazz != this.getUpToClass()) {
            clazz = clazz.getSuperclass();
            this.appendFieldsIn(clazz);
        }
        return super.toString();
    }

}

ReflectionToStringBuilder.java

　　　　例如：ReflectionToStringBuilder.toString(user, ToStringStyle.MULTI_LINE_STYLE)

　　　　　　技巧01：如果一个对象没有重写 toString() 方法，调用该对象的 toString() 方法时就会调用父类Object的toString() 方法，从而输出的信息时常人看不懂的，所以需要使用ReflectionToStringBuilder来进行处理