001/* 002 * Copyright 2002-2018 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.web.servlet.tags.form; 018 019import java.io.IOException; 020 021import javax.servlet.jsp.JspException; 022import javax.servlet.jsp.tagext.BodyContent; 023import javax.servlet.jsp.tagext.BodyTag; 024 025import org.springframework.lang.Nullable; 026import org.springframework.util.Assert; 027import org.springframework.util.StringUtils; 028 029/** 030 * Convenient super class for many html tags that render content using the databinding 031 * features of the {@link AbstractHtmlElementTag AbstractHtmlElementTag}. The only thing 032 * sub-tags need to do is override {@link #renderDefaultContent(TagWriter)}. 033 * 034 * @author Rob Harrop 035 * @author Juergen Hoeller 036 * @since 2.0 037 */ 038@SuppressWarnings("serial") 039public abstract class AbstractHtmlElementBodyTag extends AbstractHtmlElementTag implements BodyTag { 040 041 @Nullable 042 private BodyContent bodyContent; 043 044 @Nullable 045 private TagWriter tagWriter; 046 047 048 @Override 049 protected int writeTagContent(TagWriter tagWriter) throws JspException { 050 onWriteTagContent(); 051 this.tagWriter = tagWriter; 052 if (shouldRender()) { 053 exposeAttributes(); 054 return EVAL_BODY_BUFFERED; 055 } 056 else { 057 return SKIP_BODY; 058 } 059 } 060 061 /** 062 * If {@link #shouldRender rendering}, flush any buffered 063 * {@link BodyContent} or, if no {@link BodyContent} is supplied, 064 * {@link #renderDefaultContent render the default content}. 065 * @return a {@link javax.servlet.jsp.tagext.Tag#EVAL_PAGE} result 066 */ 067 @Override 068 public int doEndTag() throws JspException { 069 if (shouldRender()) { 070 Assert.state(this.tagWriter != null, "No TagWriter set"); 071 if (this.bodyContent != null && StringUtils.hasText(this.bodyContent.getString())) { 072 renderFromBodyContent(this.bodyContent, this.tagWriter); 073 } 074 else { 075 renderDefaultContent(this.tagWriter); 076 } 077 } 078 return EVAL_PAGE; 079 } 080 081 /** 082 * Render the tag contents based on the supplied {@link BodyContent}. 083 * <p>The default implementation simply {@link #flushBufferedBodyContent flushes} 084 * the {@link BodyContent} directly to the output. Subclasses may choose to 085 * override this to add additional content to the output. 086 */ 087 protected void renderFromBodyContent(BodyContent bodyContent, TagWriter tagWriter) throws JspException { 088 flushBufferedBodyContent(bodyContent); 089 } 090 091 /** 092 * Clean up any attributes and stored resources. 093 */ 094 @Override 095 public void doFinally() { 096 super.doFinally(); 097 removeAttributes(); 098 this.tagWriter = null; 099 this.bodyContent = null; 100 } 101 102 103 //--------------------------------------------------------------------- 104 // Template methods 105 //--------------------------------------------------------------------- 106 107 /** 108 * Called at the start of {@link #writeTagContent} allowing subclasses to perform 109 * any precondition checks or setup tasks that might be necessary. 110 */ 111 protected void onWriteTagContent() { 112 } 113 114 /** 115 * Should rendering of this tag proceed at all. Returns '{@code true}' by default 116 * causing rendering to occur always, Subclasses can override this if they 117 * provide conditional rendering. 118 */ 119 protected boolean shouldRender() throws JspException { 120 return true; 121 } 122 123 /** 124 * Called during {@link #writeTagContent} allowing subclasses to add any attributes to the 125 * {@link javax.servlet.jsp.PageContext} as needed. 126 */ 127 protected void exposeAttributes() throws JspException { 128 } 129 130 /** 131 * Called by {@link #doFinally} allowing subclasses to remove any attributes from the 132 * {@link javax.servlet.jsp.PageContext} as needed. 133 */ 134 protected void removeAttributes() { 135 } 136 137 /** 138 * The user customised the output of the error messages - flush the 139 * buffered content into the main {@link javax.servlet.jsp.JspWriter}. 140 */ 141 protected void flushBufferedBodyContent(BodyContent bodyContent) throws JspException { 142 try { 143 bodyContent.writeOut(bodyContent.getEnclosingWriter()); 144 } 145 catch (IOException ex) { 146 throw new JspException("Unable to write buffered body content.", ex); 147 } 148 } 149 150 protected abstract void renderDefaultContent(TagWriter tagWriter) throws JspException; 151 152 153 //--------------------------------------------------------------------- 154 // BodyTag implementation 155 //--------------------------------------------------------------------- 156 157 @Override 158 public void doInitBody() throws JspException { 159 // no op 160 } 161 162 @Override 163 public void setBodyContent(BodyContent bodyContent) { 164 this.bodyContent = bodyContent; 165 } 166 167}