Jackson 基础

Jackson是一个高效的java bean 到json的转换工具，项目主页http://jackson.codehaus.org/

 

Jackson提供了三种处理Json的方法，分别是：

Streaming API ：基于独立事件模型处理JSON。效率最高，是下面两种方式的基础。

分别用org.codehaus.jackson.JsonParser 和 org.codehaus.jackson.JsonGenerator 读写Json

 

Tree Model ：基于一个可变的树表示一个Json模型。最灵活

org.codehaus.jackson.map.ObjectMapper 创建树（基于JsonNode为节点）

Tree Model与XML DOM类似

 

Data Binding：用属性存取或者注释来处理从Json到POJO的转换。最方便，常用这种API

有简单绑定和全数据绑定，同样用org.codehaus.jackson.map.ObjectMapper处理

 

 

下面是Data Binding方法的基本使用

首先是将java bean转换为JSON

public static void main(String[] args) { TestGridBean bean=null; Vector vec = new Vector(); for(int i=0;i<1000;i++) { bean = new TestGridBean(); bean.setNo(i); bean.setName("姓名"+i); bean.setMathscore(i); bean.setEnscore(i); vec.add(bean); } //ObjectMapper 线程安全具有缓存机制，重用可显著提高效率，实际使用中可设为全局公用 ObjectMapper mapper = new ObjectMapper(); //用此类构造字符串 StringWriter w=new StringWriter(); try { //writeXXX方法是将对象写成JSON，readXXX方法是将JSON封装成对象 mapper.writeValue(w, vec); } catch (JsonGenerationException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } String s = w.toString(); S.echo(s); } 

 

然后是JSon到java bean 的转换

用GT-Grid前台传入的表格参数json为例，其格式为形如：

{"recordType":"object", "pageInfo":{"pageSize":20,"pageNum":1,"totalRowNum":-1,"totalPageNum":0,"startRowNum":1,"endRowNum":-1}, "columnInfo":[ {"id":"no","header":"学号","fieldName":"no","fieldIndex":"no","sortOrder":null,"hidden":false,"exportable":true,"printable":true}, {"id":"name","header":"姓名","fieldName":"name","fieldIndex":"name","sortOrder":null,"hidden":false,"exportable":true,"printable":true}, {"id":"total","header":"总成绩","fieldName":"total","fieldIndex":"total","sortOrder":null,"hidden":false,"exportable":true,"printable":true}, {"id":"detail","header":"详细信息","fieldName":"detail","fieldIndex":"detail","sortOrder":null,"hidden":false,"exportable":true,"printable":true} ], "sortInfo":[], "filterInfo":[], "remotePaging":true, "parameters":{}, "action":"load"} 

以上json对应的java bean应该是如下格式：

package gxlu.ims.webapps.action.syncResultQuery; import java.io.Serializable; public class GTGridBean implements Serializable { /** * */ private static final long serialVersionUID = 1L; private String recordType; private String[] sortInfo; private String[] filterInfo; private boolean remotePaging; private String action; private PageInfo pageInfo; private ColumnInfo[] columnInfo; private Parameters parameters; public static class PageInfo { private String pageSize; private long pageNum; private long totalPageNum; private long totalRowNum; private long startRowNum; private long endRowNum; public String getPageSize() { return pageSize; } public void setPageSize(String pageSize) { this.pageSize = pageSize; } public long getPageNum() { return pageNum; } public void setPageNum(long pageNum) { this.pageNum = pageNum; } public long getTotalRowNum() { return totalRowNum; } public void setTotalRowNum(long totalRowNum) { this.totalRowNum = totalRowNum; } public long getStartRowNum() { return startRowNum; } public void setStartRowNum(long startRowNum) { this.startRowNum = startRowNum; } public long getEndRowNum() { return endRowNum; } public void setEndRowNum(long endRowNum) { this.endRowNum = endRowNum; } public long getTotalPageNum() { return totalPageNum; } public void setTotalPageNum(long totalPageNum) { this.totalPageNum = totalPageNum; } } public static class ColumnInfo { private String id; private String header; private String fieldName; private String fieldIndex; private String sortOrder; private boolean hidden; private boolean exportable; private boolean printable; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getHeader() { return header; } public void setHeader(String header) { this.header = header; } public String getFieldName() { return fieldName; } public void setFieldName(String fieldName) { this.fieldName = fieldName; } public String getFieldIndex() { return fieldIndex; } public void setFieldIndex(String fieldIndex) { this.fieldIndex = fieldIndex; } public String getSortOrder() { return sortOrder; } public void setSortOrder(String sortOrder) { this.sortOrder = sortOrder; } public boolean isHidden() { return hidden; } public void setHidden(boolean hidden) { this.hidden = hidden; } public boolean isExportable() { return exportable; } public void setExportable(boolean exportable) { this.exportable = exportable; } public boolean isPrintable() { return printable; } public void setPrintable(boolean printable) { this.printable = printable; } } public static class Parameters { } public String getRecordType() { return recordType; } public void setRecordType(String recordType) { this.recordType = recordType; } public PageInfo getPageInfo() { return pageInfo; } public void setPageInfo(PageInfo pageInfo) { this.pageInfo = pageInfo; } public String[] getSortInfo() { return sortInfo; } public void setSortInfo(String[] sortInfo) { this.sortInfo = sortInfo; } public String[] getFilterInfo() { return filterInfo; } public void setFilterInfo(String[] filterInfo) { this.filterInfo = filterInfo; } public boolean isRemotePaging() { return remotePaging; } public void setRemotePaging(boolean remotePaging) { this.remotePaging = remotePaging; } public String getAction() { return action; } public void setAction(String action) { this.action = action; } public static long getSerialversionuid() { return serialVersionUID; } public Parameters getParameters() { return parameters; } public void setParameters(Parameters parameters) { this.parameters = parameters; } public ColumnInfo[] getColumnInfo() { return columnInfo; } public void setColumnInfo(ColumnInfo[] columnInfo) { this.columnInfo = columnInfo; } }  

使用jsckson转换的代码：

public void testPageData() throws Exception { String json = req.getParameter("_gt_json"); S.echo(json); //将json转换为java bean用readXXX方法 Object obj = mapper.readValue(json, GTGridBean.class); S.echo(obj); }